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The REXX Interpreter (Experimental Version) This is a reference for the various language features supported by the REXX/imc interpreter. An introduction, summary and technical reference may be found in rexx.info, rexx.summary and rexx.tech, respectively. Oxford Note: There are two versions of the REXX/imc executable file, for sun3 and sun4 architectures: these are kept in /mclab/imc/sun3/rexx and /mclab/imc/sun4/rexx respectively. An executable shell script is kept in /mclab/imc/misc/rexx; this invokes the appropriate binary file. Unfortunately, placing "#!/mclab/imc/misc/rexx" at the top of a Rexx program does not work because it is not a binary file. _________________________________________________________________________ Invocation: rexx [flags] filename args where "filename" is the name of the REXX program you wish to execute, and "flags" are some optional commandline parameters, described later. Notes: 1. If the basename of "filename" does not contain a dot, then an interpreter-supplied extension (usually ".exec") will be appended, and will become the "default extension". Otherwise, nothing will be appended and the given name's extension will become the default extension (the default extension is referenced when calling external functions). 2. The argument string may be any sequence of characters, including spaces, but not including NULs (\0). Bear in mind that quotes and/or escape characters may be necessary, because the csh shell interprets some characters as special and removes multiple spaces. 3. The REXX program is assumed to be a text file whose lines are separated by newline characters: thus newline characters may not appear in the middle of a line. All other characters are allowed (but many characters are rejected unless they form part of a string constant or comment). 4. If the given filename does not include a path specification, then the interpreter will search through the directories listed in the PATH environment variable (if any), before looking in the current directory. The current directory may be placed in PATH to change this searching order (but this is disrecommended because it is a possible security risk in Unix). Thus "rexx -ta test hello there" will call the program "test.exec" with argument "hello there" and flag "-ta". The flags which are allowed all start with a "-" and are case- insensitive. They are: -option where "option" is any option recognised by the OPTIONS instruction (see below), for example: -tracefile=test1 -s string The interpreter will execute the contents of "string" as though it were a program. The string may contain newline characters, which will be recognised as line terminators (in contrast to the string which appears in an INTERPRET instruction). Note that if the string contains any shell metacharacters (including spaces) then it must be quoted to prevent the shell from interpreting it or splitting it up. -t setting The interpreter will execute "TRACE setting" before interpreting the program. The space before the setting may be omitted, for example: -t?i. Note that the setting may need to be quoted, because "?" is a shell metacharacter. -i This equals "-t?a -s 'do forever;nop;end'". The interpreter will enter interactive mode for you to type Rexx instructions. -x This option is used for files with the execute bit set on: it prevents an ".exec" from being appended to the filename, and it causes the first line of the file to be ignored (see below). Except in the case that -i or -s is present, if a filename is omitted or "-" is specified then REXX/imc reads a program from the standard input. The option "-x" and the filename "-" terminate the commandline flags. The following parameter is assumed to be a filename (except when -i, -s or - have been specified) followed by the Rexx program parameters. To execute a program called "-", say "rexx -x -". REXX/imc allows you to write a program starting with the line: #!/path/rexx -x (where /path/rexx is the absolute path name of the interpreter) at the top of the file so that the program can be made executable by the system. REXX/imc will ignore the above line (as it doesn't make sense in REXX) because of the -x supplied as an option. The line will still be there, however, so line numbers in error reports will be correct (the `sourceline' function will also recognise the existence of this line). In fact REXX/imc always ignores the first line if it starts with the characters "#!", but using the -x parameter allows a further trick: in order to write a rexx program which is able to be executed on either a sun3 or a sun4, the first line of the program should not be as above, but as follows: exec rexx -x "$0" "$*" as long as "rexx" can be found in a directory which is on the current path. Oxford note: instead of the above, the following line specifies the correct path name: exec /mclab/imc/`/bin/arch`/rexx "$0" "$*" The Rexx interpreter needs access to the program "rxque" and (if math functions are called) "rxmathfn.*" (where * is either exec or rxfn). The interpreter has several places to look for these files, and it will use the first directory in which it finds "rxque" at initialisation time. (Note: this means that changing the value of REXXIMC while the interpreter is running has no effect). The interpreter will search for "rxque" in the following directories: - that named by REXXIMC, if this environment variable is set. If it is not set, then a default which was chosen at compile time is used instead. - the path name used when invoking Rexx, if any. That is, if you type "/foo/rexx myexec", then /foo will be searched. If you type "rexx myexec", then this step will be skipped. - the directories named in the environment variable PATH - the current directory. It should not be necessary to set REXXIMC, but under certain circumstances it may speed up the initialisation time to do so. _________________________________________________________________________ The REXX Language, as interpreted by this implementation ======================================================== NOTE: There will occasionally be comments headed by `NOTE', `BUG' or `LOCAL'. The notes following these will usually be in the following categories: NOTE - (semi-)important information, pointing out traps or differences with other implementations. BUG - a feature of the program (not always a particularly bad one, though never beneficial) which may not get fixed. LOCAL- a feature of the interpreter which I have deliberately added and is not `real' REXX NOTE: Just because any particular description does not contain a note headed by `LOCAL', that does not necessarily mean that the relevant function behaves exactly according to the REXX specification. It does mean, however, that I would like to know of such instances where there is a difference, so that I can either change the program or add a note to describe the behaviour. The use of non-implemented REXX constructs will produce either error 82 (Syntax error) or error 81 (Un-implemented function). _________________________________________________________________________ Summary: Expressions Built-in functions Instructions: NOP SAY, SAYN (local) Assignment DROP NUMERIC EXIT DO LEAVE ITERATE IF SELECT PARSE QUEUE, PUSH CALL (and function calls) RETURN PROCEDURE INTERPRET SIGNAL SIGNAL ON TRACE OPTIONS ADDRESS Commands to the environment The REXX I/O model The stack Error messages _________________________________________________________________________ Expressions Every expression evaluates to a string. There are no numeric expressions, but arithmetic may be performed on those strings which happen to represent numbers in decimal. From here on, references to "numbers" or "numeric" values will mean strings of the following format: [+|-] [nnnnn][.][nnnn] [E [+|-] nnn] That is, an optional sign followed by a string of digits, possibly including a decimal point, followed by an optional exponent. The exponent consists of a letter `E' (or `e'), an optional sign, and a sequence of digits. No spaces are allowed within a number, but trailing or leading spaces are allowed, and spaces may occur between the leading sign and the first digit. There is no number which contains no digits before the exponent (if any), and "." is not a number. Whenever REXX constructs a number (such as the result of an arithmetic operation), it is formatted according to the following rules: - a zero result is always expressed as the single digit "0". - it is rounded up or down if necessary, so that the specified number of significant figures is not exceeded. The number of significant figures is usually 9, but can be changed with the NUMERIC DIGITS instruction. - If the number is negative, it is preceded by a minus sign, otherwise there is no sign. A number never contains spaces. - If the magnitude of the number is less than 1 (and if exponential notation is not used) then a single zero digit precedes the decimal point. - An exponential form of the number - e.g. 1.234E+65 - will be used if the number of digits otherwise required before or after the decimal point exceeds NUMERIC DIGITS or twice that value, respectively. - If NUMERIC FORM SCIENTIFIC is in effect (the default) and the number is expressed in exponential form, then the mantissa has precisely one digit before the decimal point (if any), which is non-zero. The exponent consists of the letter E followed by a plus or minus sign, and then the exponent (with no spaces or leading zeros). - If NUMERIC FORM ENGINEERING is in effect and the number is expressed in exponential form then the exponent is a multiple of three. Up to three digits appear before the decimal point in the mantissa, but otherwise the form is similar to the `scientific' form described above. See the NUMERIC command for some more information. An expression consists of one or more constants or variables which may be combined with the use of operators and functions, as described below. Spaces are allowed within expressions, as long as they do not split up variable names or other integral items. String Constants: These are enclosed in quotes. Either single or double quotes may be used, but the terminating quote must be the same as the initial quote. A string may contain any characters, but to enclose a quote of the same kind as the delimeters, the quote is typed twice. A string containing no characters is a null string. Example: "that's right" has value that's right '"I''m here," I said.' has value "I'm here," I said. "" is the null string. Hex Constants: A hex constant contains a sequence of hex digits grouped in pairs. The first group may have just one digit, in which case a `0' is added to the left. The groups are optionally separated by spaces. Each group (pair) of hex digits is translated into the character it represents in ASCII. The list is enclosed in quotes and immediately after the terminating quote is an `X' (or `x'). The `X' must not form part of a longer word. Example: "41 4243 44 "x has value ABCD Binary Constants: A binary constant is like a hex constant, but has `B' instead of `X' and contains binary digits ("0" or "1"). The digits are arranged in nybbles - that is, groups of 4, which may optionally be separated by spaces. The first nybble may have less than 4 digits, in which case it is extended on the left with zeros. If an odd number of nybbles is present, a zero nybble is added on the left. Each pair of nybbles is then translated into an ASCII character. Example: '10 0011 00100001'b has value CA NOTE: the sequence of binary or hex digits must not contain leading or trailing blanks. Symbols: A symbol contains any number of letters, numbers, dots and the characters @#$!?_ and is always translated to upper case before use. A constant symbol is one which starts with a number or a dot, and when it is found in an expression, the characters of the symbol itself are used. In addition, a single plus or minus sign is allowed in a constant symbol if it is part of (the exponent of) a number as defined above Any non-constant symbol may be assigned a value by the statement symbol = expression A simple symbol is one which does not contain any dots and does not start with a digit. When it is used in an expression it names a variable, and if it has been assigned a value then that value is used, otherwise the symbol itself is used (after translating to upper case). A stem is a symbol which ends with a dot, but does not contain any other dots and does not start with a digit or dot. It can be used in an expression or assigned to (see below). A compound symbol is a symbol which consists of a stem followed by a tail. The tail consists of a non-empty sequence of `qualifiers' separated by dots. Each qualifier is ordinarily a simple symbol, a constant symbol, or null (that is, it contains no characters), but as a LOCAL extension, some additional qualifiers are allowed. The following can be used as qualifiers: 1. a simple symbol, which is substituted by its value before being used in the compound variable name 2. a constant symbol, which is uppercased before being used in the compound symbol 3. a null qualifier (as in `a..b') 4. a string constant 5. a parenthesised expression. The stem and all qualifiers (1) and (2) above are uppercased before use, but the value of a symbol in (1) or of a string constant or expression in (4) or (5) is not uppercased. After the name of a compound symbol has been found, if it has a value then that value is used, otherwise the name of the symbol is used (with no uppercasing). If a stem is assigned a value (as in `foo.=7'), then every possible compound symbol is given that value (so, for example, foo.bar now has value 7). If a stem is used in an expression, its value will be the last value assigned to the stem, if any (and otherwise its value will be the stem's name in uppercase). So, for example, foo. now has value 7. Examples: If foo has been assigned the value 5 but no other names have been assigned values, then: foo is a simple symbol with a value foobar is a simple symbol without a value and foo.5 foo.Foo FOO.'5' foo.(foo*3-10) all represent the same compound symbol (which has no value, so the string "FOO.5" will be used). However, foo.'bar' foo.'BAR' represent different compound symbols, each of which has no value (so the strings "FOO.bar" and "FOO.BAR" will be used respectively). LOCAL: Note that qualifiers (4) and (5) above are local extensions. Literals: A literal is another name for a constant symbol, or a non-constant symbol without a value. BUG: There is an upper limit on the length of variable names. If at any time during the interpretation of a variable name the interpreter's copy of the name is likely to exceed about 250 characters, there will be an error. Operators: Each operator described below will be given a priority. Operators are applied, from left to right, in order of their priority, 1 being carried out last. Thus, in "3+4*5/2" the operations carried out are, in order: 4*5=20 (priority 8) 20/2=10 (priority 8) 3+10=13 (priority 7) Unary operators: + 11 (+a is similar to 0+a) - 11 (arithmetical negation) ^ or \ 11 (boolean negation) Binary operators: **10 (exponentiation) * 8 (multiplication) / 8 (division) % 8 (integer division) // 8 (remainder from integer division) + 7 (addition) - 7 (subtraction) || 6 (concatenation) = 5 (equality) == 5 (strong equality) <> or >< or ^= or \= 5 (not equality) ^== \== 5 (strong nequality) < 5 <= or ^> or \> 5 (the usual relations) > 5 >= or ^< or \< 5 >> 5 (strong greater-than) << 5 (strong less-than) >>= or ^<< or \<< 5 (strong greater-or-equal) <<= or ^>> or \>> 5 (strong less-or-equal) & 3 (boolean and) | 2 (boolean or) && 2 (boolean xor) NOTE: The character `\' and the character `^' both mean `not' and are interchangeable. The preferred `not' character is `\'. In addition to these binary operations, there are two concatenation operators. Firstly, if two values are placed next to each other with no space in between (clearly they must be differentiable for this to make sense), they are concatenated, with priority 6. Secondly, if two values are placed next to each other with at least one space between, they are concatenated with a space between, with priority 6. For example, 1"+"1"="1+1 has value 1+1=2 1 "+" 1 "="1+1 has value 1 + 1 =2 NOTE: There are a small number of cases where the space operator does not give the intended result. Example: 1 -2 4 -7 does not equal 1 -2 4 -7 but it equals -1 -3 because spaces are allowed within expressions, and so this expression is interpreted as meaning 1-2 4-7 Parentheses are used in order to circumvent the usual priorities of operators, so that, for example, (1+2)*3 is 9, whereas 1+2*3 is 7. A function call consists of a function name (which is a symbol) followed immediately by a left parenthesis, a list of expressions separated by commas, and a right parenthesis. Arguments may be omitted simply by putting no expression between one comma (or parenthesis) and the next. As with simple symbols, the case of the function name is ignored unless it is a string constant. Note that a function name must not end with a dot, because in that case it would be interpreted as a compound symbol containing a parenthesised expression. There are three types of function, which are searched in the following order: 1. Internal functions (those in the current program, beginning with a label). These are not searched if the function name is a string constant. 2. Built-in functions (a list of which is given later in this section). Note that if the function name is a string constant, it must be in upper case for the search to succeed. 3. External functions (either an external executable file or an external rexx program). When an external function file is searched for, the name is always translated to lower case. If the name is a string constant then a path name may be specified. The search is caried out three times, once with ".rxfn" appended, once with the default extension (see invocation section above), and once with ".exec". If the ".rxfn" file is found, it is assumed to be an executable which will be dynamically linked in with the interpreter. NOTE: Once an executable function has been found, it becomes in effect a built-in function. When the interpreter is searching for such a function, the name is not translated to lower case, and any leading path name is ignored. However, the name of the function (i.e. that part which comes after the last slash) will usually be required to be in upper case - so "/my/directory/FUNCTION" is the preferred way to name a function in /my/directory. NOTE: The above notes about case translation will change in the future. Examples: foo(3,,6) calls an internal or built-in function named FOO, or an external function named foo or foo.exec, with arguments 3,nothing,6. 'DATE'() always calls the built-in function DATE with no arguments. "/bin/ABC"() calls an external function named /bin/abc.rxfn or /bin/abc.exec (perhaps). Arithmetic Operators: The operand(s) must be numeric values. If they are not, then an error results. The usual arithmetic rules apply. See the "NUMERIC" command. The y operand the exponentiation operator in "x ** y" must be an integer, otherwise an error results. The exponentiation operator works effectively by multiplying x by itself y times, and taking the reciprocal if y<0. (It uses an O(log y) method). The integer division operator % is defined so that x%y is the integer part of x/y (obtained by rounding towards zero), and x = y*(x%y) + (x//y) For example, 10 % 0.3 = 33 and 10 // 0.3 = 0.1 An integer is a whole number which lies within the range of the machine (-2**31 to 2**31-1). A whole number is any number with no non-zero fractional part which would not be written in exponential notation when formatted. The maximum exponent is about 999999999. An overflow or underflow will occur if the limit is exceeded. BUG: You might find that the maximum number boundary is a little `fuzzy' but if you keep below 1E999999990 you should be alright! BUG: Whole numbers must be less than 1999999999. Boolean logic: Several of the above operators operate on boolean values or create boolean values. The following rules apply: 1. The result of a binary relation or of the \ (or ^) operator is always 1 for true, 0 or false. 2. A boolean value is represented by any number (attempts to use other strings will result in an error). False is represented by zero, and any other number represents true. LOCAL: In `real' REXX a boolean value may only be represented by 0 or 1. 3. \x has the obvious meaning consistent with the above (i.e. 1 if x=0, and 0 otherwise). 4. x & y is 0 if y is false but has the same value as x when y is true. 5. x | y is 1 if y is true but has the same value as x when y is false. 6. x && y has value x if y is false, and \x otherwise. Binary relations: (note that the symbol '\' means `not' and may be placed before any of the relations to negate its value, e.g. \=, \>> etc. Thus, for instance, \> and <= have the same meaning, as do \>> and <<=, etc. The character `^` is a synonym for '\' - so ^== is the same as \==). The operators ==, \==, <<, >>, <<=, >>= compare their two operands character by character and thus have the normal meaning of string equality, greater, less, etc. All other operators depend on whether or not both operands are numeric. If they are, then they are subtracted and the result compared with zero. Otherwise, leading and trailing spaces are stripped and the operations are compared as strings usually are, with the shorter string being padded on the right with spaces before the comparison. Hence: "0.10" \== "1e-1" (strict string comparison) "0.10" = "1e-1" (numeric comparison) " hello" \== "hello " (strict comparison respects spaces) " hello" = "hello " (weak comparison strips spaces) "abc " >> "abc" (strict comparison respects spaces) "61626300"x < "616263"x (the latter is padded with a space) "61626364"x > "616263"x (ordinary string comparison) "2.5" > "10abc" (string comparison) "2.5" < "10" (numeric comparison) "2.5" >> "10 (strict string comparison) In this implementation, character comparisons are unsigned, that is to say "ff"x is greater than "00"x, etc. _________________________________________________________________________ Built-In Functions In this section, several of the function arguments are named with the following conventions: "number" must be numeric. "length" must be a non-negative whole number. "count" must be a non-negative whole number. "position" must be a positive whole number. "pad" must be a string of length 1. "option" must be a nonempty string. Only the first character of the option is significant, and it is translated to uppercase before use. "file" must be the name of a stream. This can be any nonempty string which does not contain NUL characters ('0'x). ABBREV(information,info[,length]) This returns 1 if info is a valid abbreviation of information - that is, info is a prefix of information and its length is at least that specified by the optional third argument (whose default is the length of info). If the length given is zero, then a null string is a valid abbreviation of anything. ABS(number) The magnitude of the given number is returned ADDRESS() The current environment string is returned (see ADDRESS instruction). ARG([position][,option]) This function deals with the argument(s) passed into a REXX program, function or subroutine. With no parameters, the result is the number of arguments given; that is, the position of the last explicitly specified argument. If the parameter "position" is given, then the result is the "position"th argument string, or an empty string if the argument was not supplied. If the option is supplied, its first character must be "E" or "O", standing for "Exists" or "Omitted" respectively. The result of the function is then 0 or 1, depending on whether the "position"th argument string exists or was omitted, with 1 meaning that "option" is true. Example: if a rexx function was called by: foo(5,,7) then arg() = 3 arg(1) = 5 arg(2,'e') = 0 BITAND(string1[,[string2][,pad]]) BITOR (string1[,[string2][,pad]]) BITXOR(string1[,[string2][,pad]]) These functions perform bitwise AND, OR or XOR respectively on their two string arguments (if the string2 argument is omitted, the null string is used). Before the operation, the shorter of the two string arguments is padded with the pad character. If no pad character is given, then '00'x is used for OR and XOR, and 'FF'x is used for AND (so that the extra characters remain unchanged after the operation). The operation is carried out by combining each character of string1 with the corresponding character of string2 as appropriate, and the resulting string of characters is returned. C2X, C2D, B2X, B2D, D2C, D2B, D2X, X2C, X2D: Each of these is a function taking an argument and possibly a count and returning a conversion of that argument. Each function converts an argument of a type indicated by the first character of the function name (Character, heX, Binary or Decimal) into the type indicated by the last character of the name. Examples: c2x("abc") = "616263" d2x(286)="11E" d2c(65)="A" d2b(65)="01000001" BUG: Each of the conversion functions which deal with decimal numbers is restricted to inputs which have a value of less than 2**31 when converted to an unsigned integer. Details of these functions are below: ......................................................................... B2D(binary) The binary input, which contains only '0' and '1' characters, is converted into a non-negative decimal number. B2X(binary) The binary input, which contains only '0' and '1' characters, is converted into hex digits. The length of the result is the smallest possible even number. D2B(decimal) The decimal input is converted into binary. The length of the result is the smallest possible multiple of 8. C2X(string) The n-character string is converted into 2n hex digits. C2D(string[,length]) The string is converted into a decimal number, interpreting the leftmost character as the most significant byte. If length is omitted, then the whole string is converted and the result is positive. If the length is given, then the string is truncated or padded with zero bytes on the left to give a string of this length, and is then taken to be a twos complement number. In this case the result may therefore be negative. D2C(decimal[,length]) The decimal number is converted into a string of characters (with the leftmost character being the most significant). If the length is given, then the result is truncated or sign-extended on the left to be of this length. Otherwise the length of the result is such that the leftmost character is not '00'x (for positive numbers) or 'FF'x (for negative numbers) except in the case of zero, which is converted to '00'x. D2X(decimal[,length]) The decimal number is converted into a hex number. If the length is given, then the result is truncated or sign-extended on the left to be of this length. Otherwise the length of the result is such that for positive numbers there is no leading zero, and for negative numbers there is no leading 'F' except in the case when the next hex digit is less than 8. D2X(0) returns a single zero digit. X2B(hex) Each pair of digits in the given hex string is converted to eight binary digits and these are concatenated together. Spaces are optional between pairs of hex digits, and the first "pair" of digits may contain only one digit, in which case a leading '0' is assumed. X2C(hex) The hex string is converted to characters, just as when 'hex'x is typed. Spaces are optional between pairs of hex digits, and the first byte of the string may optionally contain only one digit, in which case a leading '0' is assumed. X2D(hex[,length]) The hex string, which should contain only hex digits (and no spaces) is first truncated or extended with zeros on the left to be of the given length if necessary, and then converted into a decimal number. If the length is given, then the hex is assumed to be in twos complement notation. Otherwise the result will always be nonnegative. ......................................................................... CENTER(s,length[,pad]) CENTRE(s,length[,pad]) This function returns a string of the given length containing s. If s contains fewer than the required number of characters, then pad characters (pad, or by default, blanks) are added on each side to centre s in the result, otherwise characters are taken away from each side of s leaving the middle block of characters. If an odd number of characters needs to be added or taken away, then the right-hand side loses or gains one more than the left. CHARIN([file] [,[position] [,count]]) Reads characters from a file. See the section on the REXX I/O model. CHAROUT([file] [,[string] [,position]]) Writes characters to a file. See the section on the REXX I/O model. CHARS([file]) Finds the number of characters available for reading. See the section on the REXX I/O model. CLOSE(file) Closes a file. See the section on the REXX I/O model. COMPARE(s1,s2[,pad]) The strings s1 and s2 are compared, after first making them of equal length by adding pad characters (or spaces) to the right of the shorter. The result is 0 if the strings are identical, otherwise the position of the first character at which the strings disagree. CONDITION([option]) This function returns information about the current trapped condition (see "SIGNAL ON" and "CALL ON" for more information). If there is no such condition, then an empty string is returned. If the option is present, it must be one of the following: 'C': Returns the condition which was trapped (one of "SYNTAX", "ERROR", "HALT", "NOVALUE", "FAILURE" or "NOTREADY"). 'D': Returns a description of the event which caused the condition. For "ERROR" and "FAILURE", this is the command string which resulted in error or failure. For "NOTREADY" it is the name of the stream which was not ready. For "NOVALUE" it is the derived name of the variable which has no value. For "HALT" it is the Unix name of the signal which caused the interruption. For "SYNTAX" it is the error message which would have been displayed on the terminal if the error had not been trapped. 'I': Returns the instruction name "CALL" or "SIGNAL" as appropriate to describe how the condition was trapped. 'S': Returns the current status of the condition as "ON", "OFF" or "DELAY". If the option is omitted then 'I' is assumed. COPIES(s,count) This function returns a string consisting of "count" copies of the string s concatenated together. DATATYPE(string[,option]) This function tests the datatype of the string. If the function is called with just one argument, then the function returns "NUM" if the argument is a valid number, and "CHAR" otherwise. If both arguments are supplied, then the answer is a logical value (0 or 1) indicating whether or not string is of the type given by the option. Is s is an empty string then the answer is always 0 unless testing for a hex constant (the null string is a valid hex constant). The option must be one of the following: 'A': s is alphanumeric (containing characters only from the ranges "a-z", "A-Z" and "0-9") 'B': s contains bits (all characters 0 or 1) 'L': s is lower case (containing only "a-z") 'M': s is mixed case (containing only "a-z" and "A-Z") 'N': s is a valid number 'S': s contains characters valid in symbols (variables) 'U': s is upper case (containing only "A-Z") 'W': s is a whole number 'X': s satisfies the rules for a hex constant (i.e. contains only "0-9", "a-f", "A-F" and blanks in appropriate places). DATE([option]) The result is the date, by default in the format dd Mmm yyyy, e.g. 27 Aug 1982 (with no leading zero on the day). Alternative formats may be obtained by supplying an option parameter, of which only the first character is significant (as usual). Possible formats are: Base - the theoretical number of days in the common era (i.e. since 1/1/1 AD). On 1/1/1900 the result would be 693595. Century - the number of days so far this century (so on 1/1/1900 the result would be 1) Days - the number of days so far in this year (so on 12 Jan 86 the result would be 12) European- the date in the format dd/mm/yy Julian - the date in the format yyddd (where ddd is as in "Days" above) Month - the full name of the current month, e.g. August Normal - the same format as for no parameter, described above Ordered - the date in the format yy/mm/dd Standard- the date in the format yyyymmdd USA - the date in the format mm/dd/yy Weekday - the full name of the current day, e.g. Tuesday On the first call to DATE or TIME in an expression, a time stamp is made which is then used for all calls to these functions within that expression. Hence if multiple calls to these functions are made within a single expression, they are guaranteed to be consistent with each other. NOTE: The date function will cease to work in the year 2000. DELSTR(string,position[,length]) A substring of string is deleted and the result returned. The substring to be deleted starts at the given position and has length length. If the length is not specified, then the rest of the string is deleted. If the given position is greater than the length of the string, or if length is zero, then the string is returned unchanged. DELWORD(string,position[,count]) This function is a word-oriented version of DELSTR. It deletes the substring of string which starts at the "position"th blank-delimited word and is of "count" blank-delimited words. If there are not "position" words in the string, or if count is 0, the string is returned unchanged. The string deleted includes any blanks following the final word deleted, but does not remove any blanks preceding the first word deleted. DIGITS() The result is the current setting of NUMERIC DIGITS. ERRORTEXT(i) i must be a whole number. The result is the message that would be displayed if error i were to occur, except that it does not include information such as the name of an undefined label, etc.. If error i is not defined, then an empty string is returned. Standard Unix I/O errors may be retrieved with this function also. Just add 100 to the error number. See the section on error messages. FDOPEN(fd [,[mode] [,file]]) Open a file descriptor for reading or writing. See the section on the REXX I/O model. FILENO(file) Gives the fd number associated with a file. See the section on the REXX I/O model. FORM() The result is either "SCIENTIFIC" or "ENGINEERING", according to the current setting of NUMERIC FORM. FORMAT(number [,[before] [,[after] [,[expp] [,expt]]]] ) The given number is rounded and formatted according to the information given, as described below (note that the number is always rounded according to NUMERIC DIGITS, if necessary, before being processed by this function): If just `number' is specified, then it is formatted according to the usual rules for REXX numerics. The number is formatted, possibly in exponential form, with `before' digits before the decimal point and `after' digits after. `before' must be strictly positive and includes any leading minus sign. `after' must be non-negative. If `after' is zero, then there will be no decimal point in the output. If either `before' or `after' is omitted, then as many places as required are used. If `before' is too small then an error results. If it is too large, then leading spaces are used to fill the extra places. The number is rounded or extended with zeros as necessary in order to have `after' digits after the decimal point (note that this is not the same as TRUNC, which truncates the number rather than rounding it). The rounding rules are as usual - the first digit which is not required is checked and if it is 5 or more, the last required digit is incremented. `expt' specifies the trigger for exponential form. Exponential form is used whenever the number would otherwise require more than `expt' digits before or more than twice `expt' digits after the decimal point. If `expt' is zero, exponential form is always used. The number will be formatted according to NUMERIC FORM, and may need up to three places before the decimal point if ENGINEERING form is in effect. The default value for `expt' is the current setting of NUMERIC DIGITS. `expp' specifies the number of digits (excluding the letter E and the sign) used for the exponent. If it is zero, exponential form is never used (this overrides the setting of `expt' if necessary). Otherwise, if exponential form needs to be used, the exponent must fit in the specified width, or an error results. Leading zeros are added as necessary to make the exponent the correct width. A zero exponent, however, always causes `expp+2' spaces to be added instead of the exponent (but no spaces if expp is omitted, or is zero). If `expp' is omitted, then as many places as required are used for the exponent. Examples: (with NUMERIC FORM SCIENTIFIC and NUMERIC DIGITS 9) format('3',4) == ' 3' format('1.73',4,0) == ' 2' format('1.73',4,3) == ' 1.730' format('-.76',4,1) == ' -0.8' format('0.000') == '0' format('12345.73',,,2,2) == '1.234573E+04' format('12345.73',,3,,0) == '1.235E+4' format('1.2345',,3,2,0) == '1.235 ' format('1234567e5',,3,0) == '123456700000.000' FTELL(file) Gives the current pointer position of a file. See the section on the REXX I/O model. FUZZ() The result is the current setting of NUMERIC FUZZ. INSERT(new,target[,[n][,[length][,pad]]]) The new string is inserted into the target string after the nth character or if n is omitted or is zero, the new string is inserted before the beginning of the target string. If length is specified, then the new string is padded or truncated to that length before inserting. The default pad character is a blank. JUSTIFY(s,length[,pad]) This function first removes all surplus space from s (as per SPACE(s) ), then attempts to right-justify s in a string of "length" characters by adding spaces between the words of s. If s does not fit in a field of "length" characters, the first "length" characters of s are returned. If the optional pad character is supplied, then the words in the output string are separated by instances of that character rather than by spaces. LASTPOS(needle,haystack[,position]) This function finds the last occurrence, if any, of the needle within haystack. The answer is the position of the last occurrence if there is one (numbering from 1 to the length of haystack), or zero if needle does not occur in haystack. If the optional position is supplied, the search starts from this position instead of the end of haystack. If the needle is the empty string, zero is returned. LEFT(string,length[,pad]) The first two mandatory parameters are a string and a length. The result of this function is the leftmost "length" characters of string. If string has fewer than this many characters, then it is padded up to the required length with spaces on the right, or, if the pad character is given, with this character. Examples: left("12345",2) = "12" left("123",5,"0") = "12300" LENGTH(string) The result is the number of characters in string. LINEIN([file] [,[line] [,count]]) Inputs a line from a file. See the section on the REXX I/O model. LINEOUT([file] [,[string] [,line]]) Outputs a line to a file. See the section on the REXX I/O model. LINES([file]) Determines whether lines can be read from a file. See the section on the REXX I/O model. LINESIZE() The function attempts to find out the terminal width using a TIOCGWINSZ ioctl on the terminal, and returns the answer. If the ioctl returns an error (for instance because there is no controlling terminal), then zero is returned. MAX(number[,number...]) This function returns the maximum of a non-empty list of numbers. MIN(number[,number...]) This function returns the minimum of a non-empty list of numbers. OPEN(path [,[mode] [,file]]) Opens a file for reading and/or writing. See the section on the REXX I/O model. OVERLAY(new,target[,[position][,[length][,pad]]]) The new string is padded or truncated to the given length and overlaid on to the target string starting at the given position. The default position is 1, that is, the start of the target string. PCLOSE(file) Closes a file which was opened by POPEN. See the section on the REXX I/O model. POPEN(command [,[mode] [,file]]) Opens a pipe to a shell command. See the section on the REXX I/O model. POS(needle,haystack[,position]) This function finds the first occurrence, if any, of needle within haystack. The answer is the position of the occurrence if there is one (starting from 1) or zero if needle does not occur in haystack. If the optional position is supplied, the search starts from this position instead of 1. If the needle is the null string, zero is returned. QUEUED() This function returns the number of entries on the REXX stack. RANDOM([min][,[max][,seed]]) A pseudo-random number is returned. If no arguments are supplied, the number will be between 0 and 999 (inclusive). If one argument is supplied then the result will be between 0 and that number. If both min and max are given, then the result will be between min and max inclusive. min must be no greater than max and the magnitude of the range (that is, max - min) must not exceed 100000. min, max and seed must be whole numbers if they are specified. Usually the third argument (the seed) is not supplied. In this case, on the first call to this function the random number generator is seeded from the system clock, and the seed is not affected on further calls, so that a `good' sequence of random numbers is obtained. The seed may be set to a specific value on each call by supplying the third argument. To gain a predictable sequence of random numbers, the seed is specified on the first call but not on subsequent calls. REVERSE(string) The function returns the reverse of string. RIGHT(string,length[,pad]) In a similar manner to LEFT, this function returns the rightmost "length" characters of string. If the string is too short then it is padded on the left with spaces, or with the pad character if this is supplied. SOURCELINE([i]) If i is omitted, then the result is the number of lines in the program. Otherwise, i must be an integer between 1 and sourceline() and the result is the ith program line. SPACE(s[,[count][,pad]]) This function formats the blank-delimited words of s with "count" pad characters between each word and with no leading or trailing blanks. The default for "count" is 1, and the default pad character is a space. If "count" is 0 then all blanks are removed. STREAM(stream[,[option][,command]]) This function examines or executes a command upon a stream. See the section on the REXX I/O model for more information. STRIP(string[,[option][,char]]) Up to three parameters may be supplied. The first is a string upon which the operation is performed - this normally consists of stripping leading and trailing spaces. The second parameter, if supplied, must start with one of the letters "L", "T" or "B". This means strip leading spaces, trailing spaces, or both, respectively. The third parameter, if supplied, must be a single character, in which case this character is stripped instead of spaces. Example: strip("000123450","l","0") = "123450" SUBSTR(string,position[,length[,pad]]) This function makes a substring of string. Usually the parameters string, position and length are supplied and the result is the substring of string of length "length" starting at the "position"th character - so substr("abcdefg",3,2) = "cd". If the length is omitted, then the substring continues to the end of the string - so substr("abcdefg",4) = "defg". If part of the substring requested is outside of string, then spaces are added - or if the parameter pad is given, this character is used to pad the result. Thus substr("abc",2,4,"0") = "bc00" and substr("abc",-1) = " abc". LOCAL: REXX/imc allows the position to be a negative whole number. SUBWORD(string,position[,count]) A substring of the given string is returned, starting at the "position"th blank-delimited word, and of length "count" words. If "count" is not specified, then the rest of the string, starting at the "position"th word, is returned. The result never contains leading or trailing blanks, but it contains all spaces between the words extracted. SYMBOL(name) The argument is interpreted as a symbol (or a number); it is uppercased, and if it is a compound symbol, any simple symbol components of the tail are substituted in as with the VALUE function. The result is the three character string "BAD", indicating that the name is not a valid symbol, "VAR", indicating that the name is a variable (i.e. a symbol which has been assigned a value), or "LIT", indicating that the name is either a constant symbol or a symbol without a value. For example, the program: b='*'; a.b=5 say symbol('a') symbol('b') symbol('a.B') symbol(A.b) say symbol('a.*') symbol('b.a') symbol('b.*') would say "LIT VAR VAR LIT" and "BAD LIT BAD". TIME([option]) The result is the time, by default in the format hh:mm:ss (in 24 hour clock). Alternative formats may be obtained by supplying an option parameter. Possible formats are: Civil - hh:mmxx where hh is the hour in 12-hour notation (no leading zeros), mm is the minute, and xx is either am or pm. Normal - the same format as for no parameter, described above Long - hh:mm:ss.uuuuuu where uuuuuu is the number of microseconds Hours - the number of hours since midnight Minutes - the number of minutes since midnight Seconds - the number of seconds since midnight Elapsed - On the first call the result is 0 and on subsequent calls the result is the elapsed time since then in the format mmmmm.uuuuuu (no leading zeros) Reset - same as Elapsed, but after the time is calculated, the timer is reset to zero. On the first call to TIME or DATE in an expression, a time stamp is made which is then used for all calls to these functions within that expression. Hence if multiple calls to these functions are made within a single expression, they are guaranteed to be consistent with each other. Note that this means that: say time(e) sleep(2) time(e) x exit sleep:'sleep' arg(1) x=time(e) return "" will type "0 0 2.374357" (perhaps) even though over two seconds elapse during evaluation of sleep(2). Also, the timestamp only applies to time() calls within a single expression, so the line "x=time(e)" is not affected by the timestamp. The elapsed time counter is saved across function calls. This means that although a procedure inherits the elapsed time counter from its caller, but if it should reset the clock, this does not affect any timing which may be in progress by the caller. NOTE: The time is subject to the accuracy of the system clock, which may not give a very reliable number of microseconds. TRACE([setting]) The result is the current trace setting, consisting of one upper case letter, possibly preceded by a single question mark. If the setting is supplied as a parameter, then this is used as a trace setting for all further execution. See the TRACE command for details. TRANSLATE(string[,[tableo][,[tablei][,pad]]]) This function translates characters in string to other characters, or may be used to change the order of characters in a string. If neither translate table is specified, then the string is translated into uppercase. Otherwise each character of string which is found in tablei is translated into the corresponding character in tableo - characters which are not found in tablei remain unchanged. The default input table is XRANGE('00'x,'ff'x) and the default output table is the null string. The output table is padded or truncated in order to make it the same length as the input table, the default pad character being a blank. Examples: translate('abc123DEF') == 'ABC123DEF' translate('abbc','&','b') == 'a&&c' translate('abcdef','12','ec') == 'ab2d1f' translate('abcdef','12','abcd','.') == '12..ef' translate('4123','abcd','1234') == 'dabc' TRUNC(number[,length]) The number is rounded as necessary according to NUMERIC DIGITS, and then truncated or padded so that the result has exactly "length" digits after the decimal point. If the length is zero or is omitted, then the result is an integer with no decimal point. The result will never be in exponential form. Examples: trunc(12.6) == 12 trunc(345e-2,1) == 3.4 trunc(26,5) == 26.00000 VALUE(s[,[newvalue][,selector]]) s is treated as a symbol, and if it has a value, that value is returned. If s is not a valid symbol then an error results. Otherwise the result is just as for a symbol appearing in a program. For compound symbols, substitution occurs as normal, except that string constants and expressions (types 4 and 5 in the description of symbols above) are not allowed. If the newvalue parameter is provided, then this value is assigned to the symbol described above. The symbol's old value will be returned. If the selector is provided, then this indicates an alternative variable pool to use instead of the REXX variable pool (except that the word "REXX" is accepted as a valid name for the usual REXX variable pool). The only selector recognised by REXX/imc is the word "ENVIRONMENT", which allows the value() function to examine and alter environment variables. Note that the names and values of environment variables may not contain NUL characters. Example: the following program a=1; b='*' c.a=1; c.b=2 say value("a") value("c.a") value("c.b") value("d.b",6) say value("d.*") will output "1 1 2 D.*" then give an error, because "*" is not allowed as a component of a symbol (however "b" is, even if b="*"). The value of d.b after executing these lines will be 6. The instructions a=value("FOO","ENVIRONMENT") call value "FOO","bar","ENVIRONMENT" are similar to the instructions a=getenv("FOO") call putenv "FOO=bar" respectively. VERIFY(string,reference[,[option][,position]]) This verifies that the string contains only characters from reference and returns 0 if this is true. Otherwise the result is the position of the first character in string which is not in reference. If the option is specified, its first letter must be either 'N' (nomatch) or 'M' (match). The action for 'N' is as described above. If 'M' is specified then the result is the position of the first character which matches a character from the reference, and 0 if no character from reference was found in the string. If the position is given, the verification starts from this position in the string instead of from the beginning. Examples: verify('123','1234567890') = 0 verify('1Z3','1234567890') = 2 verify('AB4T','1234567890','M') = 3 verify('1P3Q4','1234567890',,3) = 4 WORD(string,position) This function returns the "position"th blank-delimited word in string, and is identical to SUBWORD(string,position,1). If there are not "position" words in string then the empty string is returned. WORDINDEX(string,position) This function returns the character position of the "position"th blank-delimited word in string, or 0 if there are not that many words in string. WORDLENGTH(string,position) This function returns the length of the "position"th blank-delimited word in string, and is identical to LENGTH(WORD(string,position)). If there are not that many words in string then 0 is returned. WORDPOS(phrase,string[,position]) This is a word-oriented version of POS. It returns the word number of the first occurrence of the phrase in the string. If "position" is specified, the the search starts at the specified word number instead of the beginning. If phrase contains no words, then 0 is returned. phrase is a sequence of blank-delimited words which must be present in sequence in the string and match exactly, except that multiple blanks between words are treated as single blanks, and leading and trailing blanks are ignored. This function replaces the FIND function from VMREXX. WORDS(string) This function returns the number of blank-delimited words in the string. XRANGE([a[,b]]) This function returns a range of ascii characters in a string. If they are supplied, a and b must be single characters. The defualt values for a and b are '00'x and 'ff'x respectively. The result is a string consisting of ascii characters in sequence starting with a and ending with b. If a>b then a string of (b-a+257) characters is returned, starting at a and ending at b, wrapping around from 'ff'x to '00'x. UNIX Specific Functions: The following functions are built into this version of REXX, although they are not standard REXX functions. Most of these functions appear in the literature. NOTE: many of these functions which accept string arguments will ignore any characters after (and including) a "00"x character. CHDIR(directory) This function attempts to change to the named directory, and returns an error code. The code is zero if no error occurred, otherwise the message corresponding to the code can be obtained with the ERRORTEXT function by first adding 100 to the number. GETCWD() The current working directory name is returned. If an error occurs while attempting to name the current directory then an error message is returned instead. The first character of the result is a `/' if and only if no error occurred. GETENV(name) If the current environment contains the named variable, then its value is returned. Otherwise an empty string is returned. This call is equivalent to VALUE(name,,"ENVIRONMENT"), and it may be deleted in a future release. PUTENV(string) The string must be of the form "variable=value". The specified environment variable is set to the given value and zero is returned. If an error occurs then 1 is returned. This call is similar to VALUE(variable,value,"ENVIRONMENT"), and it may be deleted in a future release. SYSTEM(s) This function takes the string s, passes it to a bourne shell, and returns as a result all text produced by that shell command on the standard output. This function has a side effect, namely that the variable `rc' is set to the exit status of the shell, or -1 if the shell couldn't be invoked for some reason. This may in turn cause the condition "ERROR" or "FAILURE" to be trapped (see the SIGNAL ON and CALL ON instructions). Except in the case that a "SIGNAL" occurs, there will always be a result whatever the return code, but it may be the null string if an error occurred (or if the command produced no output). USERID() The result is the login-name corresponding to the owner of the interpreter process. If that cannot be determined for some reason, an empty string is returned. Mathematical Functions The following functions are treated as built-in functions, although they are usually calculated by an external program (supplied with REXX). In this version, all calls to these functions are directed to /mclab/imc/sun{3|4}/rxmathfn. This is usually an executable, but a REXX program is also provided as an alternative. Whichever is found by the interpreter will be used. All the functions described below give results according to the current setting of NUMERIC DIGITS, but they use floating-point maths so a maximum of about 16 digits of accuracy may be obtained. The exception is the square root function, which can always give the required number of digits of accuracy (subject to machine resources). ACOS(x) the arc-cosine of x in radians (0<=acos(x)<=pi) ASIN(x) the arc-sine of x in radians (-pi/2<=asin(x)<=pi/2) ATAN(x) the arc-tangent of x in radians (-pi/2<=atan(x)<=pi/2) COS(x) the cosine of x radians EXP(x) the exponential of x (2.718281... to the power x) LN(x) the natural logarithm of x (x>0) SIN(x) the sine of x radians SQRT(x) the square root of x (x>=0) [arbitrary precision possible] TAN(x) the tangent of x radians (x <> pi/2) TOPOWER(x,y) x to the power y (like x**y except non-integer values of y are allowed). If y=0 then the result is 1. If x=0 and y>0 then the result is 0. Otherwise the result is exp(y*ln(x)). _________________________________________________________________________ Instructions Comments are supported, and may appear anywhere that a space can, with the exception that comments are not allowed within a multi-character operator (e.g. ** or ==). They can occupy any number of lines and may be nested. /* This is a comment. It is started by /* and ended by */. */ The star and slash characters of the comment delimiters must not be separated by whitespace. Each command must usually appear all on one line. The exception to this rule is when a line ends with a comma. In this instance, the comma is deleted and the next line appended with a space. Multiple lines may be appended in this way. Thus say, /* spaces and/or comments may follow the comma */ "this is", "a test" will actually be interpreted as say "this is" "a test" and will result in this is a test Note that quotation marks must always be closed before the end of a line. For example, the following will cause an error: say "this is, a test" Instructions may be separated by semicolons or by the ends of lines. The following REXX commands are currently implemented. They are displayed in upper case, but may be typed in mixed case. Square brackets indicate optional parts of constructions. _________________________________________________________________________ NOP This does nothing. It is provided for situations such as IF xxxx THEN NOP ELSE yyyy. _________________________________________________________________________ SAY [expression] The expression is evaluated and displayed on the standard output, followed by a newline character. If no expression is supplied then just the newline character is output. LOCAL: The command: SAYN expression evaluates the expression and displays it without a newline character. Note that a similar effect can be obtained with the function call charout, though the output may have to be flushed by calling charout a second time with no parameters. _________________________________________________________________________ symbol=value If `symbol' is a simple or compound symbol then it is assigned the value `value', so that assignment in REXX has the usual meaning. A compound symbol is subject to the usual substitution of qualifiers. If `symbol' is a stem, then all possible compound symbols which start with the given stem are assigned the value `value'. Variables are allowed to have the same names as REXX keywords, with the exception of some keywords within particular commands (e.g. "until" in a DO construction). The following rule is applied, in order to distinguish between an assignment and any other command: if the first word in the line is followed by an `=' (after optional spaces), then it is an assignment. This does not apply, however, to constant symbols, which can not be assigned to. _________________________________________________________________________ DROP symbol [symbol,...] The DROP command un-assigns each symbol named after the DROP keyword. Simple or compound symbols or stems may be dropped. If the symbol is a stem, then all compound symbols starting with that stem are dropped. If a variable has been passed to a procedure with the PROCEDURE EXPOSE construction, then the variable in the calling procedure will be dropped also. If a dropped symbol is subsequently assigned a value, then the variable will also be assigned that value in the calling procedure. It is not an error to DROP a non-existent symbol, or to DROP a symbol twice. NOTE: Even if a compound variable is dropped, its value will always be undefined immediately after the drop. For example, stem.="Some value" drop stem.6 say stem.5 stem.6 stem.7 makes stem.6 undefined and says "Some value STEM.6 Some value". _________________________________________________________________________ EXIT [expression] The EXIT instruction returns control from a program to its most recent external caller. This will either be a rexx external call (that is, `CALL name' or `name()' where name is the name of the REXX program rather than an internal or builtin function name) or a UNIX command, if the program was not called by another REXX program. All the current DO, SELECT, INTERPRET and internal call structures are terminated, and control resumes at the point of the most recent external call. An expression may follow the EXIT statement; this is passed back to the caller in the same way as in the RETURN statement. If control is returned back to UNIX, then the expression must be an integer if it is supplied, and it is used as the exit value of the interpreter. If no value is supplied then the exit code will be zero. Note that reching the end of a program is the same as executing "EXIT". In other words, reaching the end of a program terminates all internal function calls. _________________________________________________________________________ NUMERIC DIGITS n NUMERIC FUZZ n NUMERIC FORM SCIENTIFIC | ENGINEERING | "string constant" | [VALUE] expression The expression evaluator uses arbitrary length arithmetic for numeric operations. The precision to which operations are carried out by the evaluator may be altered using the NUMERIC DIGITS command, and is initially 9. The number supplied will be the number of digits kept after each operation, not including the decimal point, or leading zeros, which are dropped by all arithmetic operations. The upper limit for NUMERIC DIGITS is about 10000 (defined in const.h). Note that a single multiplication or division can take many minutes at this precision. NUMERIC FUZZ is initially zero and is set to zero by each NUMERIC DIGITS command. It specifies a temporary reduction in the precision of arithmetic when doing comparisons (remember, for all numeric comparisons, the two operands are subtracted and the result is compared with zero. It is the precision of the subtraction which is affected by NUMERIC FUZZ). The upper limit for NUMERIC FUZZ is clearly one less than the current value of NUMERIC DIGITS. NUMERIC FORM is used to set the form of exponents to either `scientific' mode or `engineering' mode. When an exponent is used, in the scientific mode there is always precisely one digit, which is non-zero, before the decimal point. In engineering mode, there are up to three digits before the decimal point, and the exponent is always a multiple of three. If an expression is used, it must evaluate to "SCIENTIFIC" or "ENGINEERING" in upper case. If the expression does not start with a symbol or string constant, then the keyword VALUE may be omitted. The NUMERIC settings are saved across function calls, and restored on return from a function, so a function may set the precision, etc. that it needs without affecting the caller. Moreover, the settings will be restored to their default settings just after entering any external REXX procedure. _________________________________________________________________________ DO There are two uses of DO: 1. DO ...commands... END This is a compound statement, i.e. the DO and END are wrapped around the block of commands so that they appear like one statement and may be used in IF constructs. 2. DO [ symbol=start [TO finish] ] [WHILE expression_w] [ [BY step ] ] [ [FOR count ] ] [UNTIL expression_u] [ expression_c ] [FOREVER ] ...commands... END [symbol] where start, finish, step, count and the expressions are numerical expressions. Expression_c and count are required to be non-negative integers. This is a repetitive command. If `symbol' is present in the DO statement, then: a. `symbol' may be any simple or compound symbol b. the symbol name may appear after the END statement; if it does, then it must be the same one as after the DO. The DO symbol and the END symbol are compared literally, without substituting any components in the tail of a compound symbol, but the comparison is case insensitive. c. the value of start is assigned to the symbol before the loop is entered. d. if [TO finish] is present, then the loop is not executed after the control variable (named by the symbol) passes the finish value. If it is not present, then the loop may potentially be executed for ever (unless a FOR clause is present). e. if [BY step] is present, then the variable is incremented by step after each pass. Otherwise the variable is incremented by 1. f. If [FOR count] is present, then the loop is executed at most count times. g. The TO, FOR and BY clauses may be specified in any order. (Note: each should be specified at most once, but specifying one or more of these twice will not cause an error. The last one encountered is the one which is used). If `symbol' is not present, then nothing must follow the END. If the expression_c is specified, then the loop is executed this number of times (unless terminated by some other condition). Note that expression_c must not start with a symbol followed by '=', because it would then be taken to be a `symbol' as above. This may be prevented by enclosing the expression in parentheses. If a WHILE clause is present, then expression_w is evaluated before each pass and the loop is terminated if the result is false. If an UNTIL clause is present, then expression_u is evaluated after each pass and the loop is terminated if the result is true. A `DO FOREVER' instruction creates a loop which never terminates (unless a LEAVE instruction is encountered). Note that if expression_w is false or if the variable clause needs no repetition, or if count or expression_c is zero, then the body of the loop will not be executed at all. An END must appear for each DO construct, and if labelled with a symbol, must have the correct symbol. NOTE: The name of any variable specified at the DO statement is evaluated again each time it is incremented at the end of a pass through the loop. This means, for example, that in "DO a.i=1 TO 10", the name of the variable which is incremented depends on the current value of i. (Altering the value of i is, of course, not highly recommended). Example: The code do name=expri to exprt by exprb for exprf while exprw (or until expru) ... instructions ... end will be executed as if it were written thus: $tempi = expri /* variables staring with $ are */ $tempt = exprt /* invisible to the rest of the */ $tempb = exprb /* program. */ $tempf = exprf name = $tempi + 0 $loop: if name > $tempt then goto $end /* "goto" is a pseudo-op */ if $tempf = 0 then goto $end /* meaning the obvious */ if \exprw then goto $end ... instructions ... $iter: if expru then goto $end /* "iterate" will come here */ name = name + $tempb $tempf = $tempf - 1 goto $loop $end: /* "leave" will come here */ (If any of the constructs in the original code are left out, the coresponding lines will be left out of this example). _________________________________________________________________________ LEAVE [symbol] If a symbol name is not specified, then LEAVE leaves the innermost repetitive DO statement by jumping to the statement after the END statement for that loop. If a symbol name is specified, then LEAVE leaves the innermost loop with that symbol as control (i.e. where the DO statement specified that symbol) - this may involve leaving several inner loops. The specified symbol must match that in the DO instruction literally, except that case is ignored. The LEAVE statement will not return from procedures or functions. If there is no suitable loop to leave within the current function or procedure call, then an error results. NOTE: LEAVE will not exit from a string being interpreted: it is an error to use LEAVE within INTERPRET unless the corresponding DO occurs there as well. _________________________________________________________________________ ITERATE [symbol] This instruction is similar to LEAVE, but instead of leaving the loop it jumps to execute the END statement and possibly continue with another iteration around the loop. The same NOTE applies. _________________________________________________________________________ IF expression [;] THEN [;] instruction [ ; ELSE [;] instruction] This construction has the obvious meaning. Note that the THEN and ELSE must be followed by single instructions, but the DO-END or SELECT-END (qv) and even IF-THEN-ELSE constructions count as single instructions for this purpose. A semicolon or line-end may optionally appear between the expression and the THEN, but one must appear before ELSE, as above. IF statements may be nested, but note that each ELSE statement corresponds to the most recent IF statement without an ELSE. If a null THEN or ELSE clause is needed, the NOP instruction must be used (as a null statement is just ignored by REXX). BUG: There is at present no way to detect incorrectly positioned ELSE statements. If an ELSE is detected during program interpretation, this will just cause the interpreter to skip the following statement and will not be an error. This bug also prevents the interpreter from flagging a construction such as "if expr then else ..." since in that case the "else" will be considered to be the statement to execute when expr is true. _________________________________________________________________________ SELECT [expression] WHEN expression THEN instruction WHEN expression THEN instruction ... [OTHERWISE instructions] END [SELECT] If an expression is supplied after SELECT, then this construction is like a Pascal or Modula `CASE' construction. The expression is compared with each of the other expressions in turn, until one is found that matches (using the `=' form of equality). If a match is found, then the corresponding instruction is executed. If a match is not found, then an OTHERWISE clause must be specified, or else an error is reported. The instructions after OTHERWISE will be executed. If an expression is not specified after SELECT, then the construction is a list of guarded commands - that is, each expression is evaluated until a true one is found, and the corresponding action is taken. Again, if no expression is true and there is no OTHERWISE then an error is reported. The word SELECT may be placed after the closing END but is optional. Adding the word SELECT allows easier detection of missing ENDs. It is an error for the word WHEN or OTHERWISE to appear anywhere except immediately inside a SELECT construction. Precisely one instruction is required after each WHEN, so NOP should be used if no action is required. NOP need not be used after OTHERWISE. If multiple instructions are required to follow each WHEN condition, then they should be contained in a DO ... END block. Multiple instructions may follow the OTHERWISE keyword. LOCAL: The optional expression following the SELECT keyword, and the optional SELECT following the END keyword are features of PL/1 and not of standard REXX. _________________________________________________________________________ [PARSE [UPPER]] ARG template [PARSE [UPPER]] PULL [template] PARSE [UPPER] LINEIN [template] PARSE [UPPER] SOURCE template PARSE [UPPER] VERSION template PARSE [UPPER] NUMERIC template PARSE [UPPER] VAR symbol template PARSE [UPPER] VALUE expression WITH template This command is a powerful parser which divides the operand up as specified by the `template'. If the UPPER keyword is specified, then the operand is uppercased before parsing. The "ARG template" and "PULL template" commands are short forms of "PARSE UPPER ARG template" and "PARSE UPPER PULL template" respectively. The possible operands are as follows: ARG - the command-line arguments, or the arguments passed by a function or procedure call, are parsed. PULL - the top value on the stack, if one exists, is parsed; otherwise a line of input is read from the standard input and parsed as described for LINEIN below. See QUEUE/PUSH for details about the stack. LINEIN- A line is read directly from stdin. The stack is not affected by this instruction. In general, PULL is recommended in preference to LINEIN. If a line cannot be read because of an I/O error or EOF condition, then the NOTREADY condition will be raised and an empty string will be parsed. The NOTREADY condition is ignored unless trapped by SIGNAL ON or CALL ON, in which case it is difficult to tell the difference between an empty input line and an I/O error. However, the STREAM() function may be used to examine the most recent I/O error on stream "stdin". NOTE: If the program is interrupted (via ^C) while input is being read, then the characters which have been read in may be lost, but the remainder of a partially-input line will remain to be read again. SOURCE- An implementation-dependent string representing the `source' of the program is parsed. In this implementation, the string contains five words: 1. the system under which the interpreter runs (always UNIX) 2. the way in which the program was called (one of COMMAND, FUNCTION or SUBROUTINE, depending whether the program was invoked by a command shell or as a function or subroutine) 3. the name of the file containing the program, with the full path name (unless no directory was specified and getwd could not name the current directory) 4. the name by which the program was called (always without a path name). 5. the environment name which was current when the program started up VERSION-A string representing the version of the REXX interpreter is parsed. This contains five words: 1. A word describing the language, of which the first four letters are always REXX. In this implementation the word is REXX/imc. 2. A string representing the version number (e.g. 1.0) 3,4,5. The date on which the interpreter was compiled, in the same format as the DATE() function (e.g. 18 May 1990). NUMERIC-The current NUMERIC settings are parsed. There are three words in the string to be parsed: NUMERIC DIGITS, NUMERIC FUZZ and NUMERIC FORM respectively. VAR - The symbol specified is evaluated, and if it represents a currently defined variable, its value is substituted. The result is then parsed. VALUE - The expression between "VALUE" and "WITH" is evaluated and then parsed (note that WITH is a reserved keyword in this instruction) If no template is supplied, the information to be parsed is collected and then thrown away. The "ARG" and "VALUE" forms may parse more than one string at once. This comes about with "ARG" when a function or procedure call (note - not a command line call) passes more than one argument, or with "VALUE" when the expression contains comma separators. In this case, the parse template may contain commas. The part of the template before the first comma applies to the first operand string, that part between the first and second commas applies to the second string, and so on. E.g. PARSE VALUE 43 56,5*9,hello,there WITH template1,template2, Here template1 applies to "43 56"; template2 applies to "5*9" and no other parsing takes place. Note that there does not have to be a template for each operand string, and also that there does not have to be an operand string for each template (in this case the extra templates will be applied to the empty string). LOCAL: Parsing multiple strings with the PARSE VALUE construction is a local extension. A parse template obeys the following grammar. A symbol in brackets indicates that that symbol may be optionally present. A character in single quotes indicates that that character should be typed literally. A symbol in double quotes is a terminal symbol, indicating the appropriate REXX entity should be present. template -> [firstPosition] assignments [assignments] assignments -> [nextPosition] varlist [stopPosition] varlist -> varname [varlist] varname -> "non-constant symbol" | '.' firstPosition -> position nextPosition -> position [nextPosition] stopPosition -> position position -> searchPosition | absPosition | relPosition | '(' "expression" ')' searchPosition -> "string constant" absPosition -> "integer" | '=' numexpr relPosition -> '+' numexpr | '-' numexpr numexpr -> "integer" | '(' "integer expression" ')' Each position symbol in this grammar indicates a column number to the parser. Positions are translated to column numbers (numbered from 1 up to l+1, where l is the length of the string being parsed) in the following way. Note that the absPosition indicator "1" is implicitly present before and after any parse template. absPosition: gives the column number directly, except that numbers not between 1 and l+1 are translated into 1 or l+1 as appropriate. searchPosition: searches for the given string constant in the string being parsed, starting from the most recent column number Usually, two column numbers result: the column number of the first character which matched, and that of the first character after the matching string. The latter number is suppressed if the next position indicator (if any) is a `relPosition'. If the string is not found, then the single column number l+1 results. "expression": evaluates the expression and then treats it as the string constant of a searchPosition relPosition: The given positive or negative number is added to the previous column number to give the result. As for an absolute position, numbers which are out of range are translated into 1 or l+1 as appropriate. For example, given the string "hello, world, hello!" and the position indicators 1 "ello" +4 ! 5 -3 'x' -2 1, the resulting column numbers would be: 1 (the given number) 2 (the first character of "ello" - the second number is suppressed) 6 (+4 characters from the previous position) 20}{(the first character of "!") 21}{(the first character after "!") 5 (the given number) 2 (-3 characters from 5) 21 (the end of the string, since "x" is not found) 19 (-2 characters from 21) 1 (the given number) The position indicators are translated into column numbers independent of the varlist, except in one case described below. Thus the parse template may be reduced by the above rules into a sequence of column numbers and varlists. Taking into account the rule that each template is implicitly prefixed and suffixed by the column number "1", each varlist thus occurs between two column numbers. Each varlist is treated separately, as follows: Denote the varlist, together with the column numbers immediately before and after the varlist, as m v1 v2 ... vk n. If m<n, or if m=n and n resulted from a search, then there exists a well-defined substring s of the string being parsed, which starts at column m and is of length n-m. (this string ends at, but does not include, column n). Otherwise, let s be that substring which starts at column m and continues to the end of the string being parsed. Then the string s is divided between the variables of the varlist by assigning the blank-delimited tokens to v1, v2, ... in order. If there are more varnames in the varlist than there are blank-delimited tokens, then the extra varnames are assigned with the empty string. The tokens assigned to varnames v1, v2, ... , v(k-1) will contain no leading or trailing blanks, but the token assigned to vk will contain all blanks which occur after v(k-1), except for the one blank immediately after v(k-1). Each varname is either a symbol name or a dot. If the varname is a dot, then the token which would be assigned to it is thrown away. Otherwise the token is assigned to it in the usual way, just as if there had been an instruction: symbol = token NOTE: Some versions of REXX allow only a symbol name between parentheses where this version allows an arbitrary expression. The one case in which the presence of a varlist may affect the translation from position indicators to column numbers is when one or more of the symbols mentioned in an "expression" is also stated in a varlist. Hence: PARSE VALUE "s/this/that" WITH 2 delim +1 first (delim) second will assign "/" to delim, "this" to first and "that" to second. This is because the variable delim is assigned as soon as the "+1" is reached. This provides a way to provide commands (such as locate commands) which take any string parameter and also some options. It allows any delimiter to separate the parameter from the options. However, PARSE VALUE "s / this/that" WITH . delim first (delim) second will not have the same effect, since delim and first are not assigned until after the expression (delim) has been searched for. Note that the symbols are assigned in order from left to right, so PARSE VALUE "1 2 3" WITH a x.a y.a will assign 1 to a, then 2 to x.1, then 3 to y.1 Other Examples: PARSE VALUE "Hello there ! etc.." WITH a b ! . "c" c will assign "Hello" to a and "there " to b, then throw away " et" and assign ".." to c. PARSE VALUE "123456789" WITH a +4 b 6 c will assign "1234" to a, "5" to b, and "6789" to c. PARSE VALUE " multiple spaces between words" WITH a b c will assign "multiple" to a, "spaces" to b and " between words" to c. PARSE VALUE "a b c d e f" WITH "b" a b "e" will assign "c" to a and " d " to b. PARSE VALUE "hello-there" WITH a "-" b -1 c +1 This assigns "hello" to a, "-there" to b and "o" to c. _________________________________________________________________________ QUEUE [expression] PUSH [expression] These instructions place the specified single expression on to the stack. If the expression is omitted, then the null string will be used. If QUEUE is used, the expression will be added in FIFO order (it will be retrieved after all currently existing stack items). If PUSH is used, the expression will be added in LIFO order (it will be retrieved before all currently existing stack items). Other programs may communicate with the REXX stack to provide data for or retrieve data from a REXX program. See the separate section on the REXX stack for details. _________________________________________________________________________ CALL name [arg][,[arg],...]] This section covers function calls as well, because evaluating a function is almost identical to calling a subroutine (even built-in functions may be CALLed). The main difference is that while a subroutine called as a function is required to return a result, a subroutine called with CALL is not required to do so. Also, calling a subroutine as a function does not cause the special variable RESULT to be set on return. The CALL command evaluates its arguments, if any, and passes them to the named function or procedure. The procedure may or may not return a result. If it does return a result, then this is assigned to the variable RESULT. The only difference between a CALL to a function and a function call (that is, between `CALL xyz args' and `xyz(args)') is that the latter expects a result and returns that to the expression evaluator (it is an error if the function does not return a result), whereas the former does not expect a result, but it assigns it to RESULT if there is one. If a called procedure does not return a result, then the variable RESULT will be dropped - that is, it will no longer have a value. As with function calls parameters may be omitted (note however that if a line ends with a comma then that comma is treated as a continuation character, so if the line needs to end with a 'real' comma then another character, such as a semicolon, needs to be added after the comma). In addition, the name may be a string constant (enclosed in quotes), in which case, as for function calls, the internal label table is not searched, and for external subroutines a path name may be specified. The name represents the name of a function (or procedure), and these are searched for in the following order: 1. internal functions 2. built-in functions 3. external binary programs 4. external REXX programs An internal function is introduced (anywhere in the current program) by a label, which takes the form name: and may be placed anywhere at the start of a statement (or on its own on a line). When an internal function is called, all labels are checked, and when a match is found, interpretation jumps to the statement immediately following the label, and continues until the next RETURN statement (or EXIT, or the end of the program). On return execution continues from the point of the call. The name may contain letters, numbers, dots and characters which are valid in symbols, but must not start with a number or dot or end with a dot. The name is translated to uppercase (except in the case of string constants) but no variable substitution occurs, even after a dot. On entry to an internal function, the special variable SIGL will be set to the line number of the instruction which caused the transfer of control. This applies equally to function calls, subroutine calls with the CALL instruction, and instructions which cause a condition handler to be called (see "CALL ON" below). An external function consists of a file, whose name contains only lowercase letters, numbers, dots and underlines. If the name given is a string constant, then it may contain a path name, but if it does not or if the name is not a string constant then the file must be in the current directory or one of the directories named in the PATH environment variable. The name given in the function call (or CALL statement) is translated to lowercase (even for string constants) and searched with ".rxfn" appended. If that file is found, then it is assumed to be a binary file. Otherwise the default extension (see section on invocation) is appended to the name and it is searched again, and again if that is not found then the search is tried again with ".exec" appended If either of these two files is found, then it is assumed to be a REXX program. Otherwise there is an error. Once an external binary function has been found, it becomes in effect a built-in function, and translation to lower case is not performed. When searching for such functions, the interpreter will ignore any leading pathname specification. An internal function may or may not hide (some or all of) its variables using the PROCEDURE command, described below. An external function, however, always has all of its variables hidden. There is therefore no way for one REXX program to affect the variables of another, except via parameters and results. (Note that data can be passed back and forth via the stack, however). The arguments to a function are picked up using the ARG variant of the PARSE command above. Example: parse arg x /* this is an example factorial program. */ say x"!="fact(x) exit fact: parse arg p /* the argument to fact is assigned to p */ if p<3 then return p return p*fact(p-1) An external function which is a ".rxfn" file must be linked (supply no flags on the command line) and have magic number ZMAGIC. Details for writing such functions are contained in the technical reference. CALL ON condition [NAME symbol] CALL OFF condition These call instructions provide error trapping. The possible conditions which may be trapped are as follows: FAILURE: A command to the environment returned a "failure" code. Usually this means a negative return code, but see the section on commands to the environment. ERROR: A command to the environment returned an "error" code. This means a non-zero return code. Note that if "failures" are not being trapped, then "error" will catch failures also. NOTREADY: A function from the REXX I/O model (see the separate section) was unsuccessful because, for example, an input function encountered an end-of-file condition. HALT: The user has attempted to halt the program, for example by typing Control-C. Signals SIGHUP and SIGTERM also raise the HALT condition. (These are the same conditions as for SIGNAL ON, except that the two conditions SYNTAX and NOVALUE may not be trapped by CALL ON). The CALL ON instruction turns on condition handling. Whenever the specified condition occurs, a CALL is made to a handling routine. If the NAME keyword is specified, then the following symbol is taken as the name of the handling routine. Otherwise the handling routine has the same name as the condition. On return from the call, execution proceeds normally. The RESULT variable will not be affected by the call. During the handling routine, the condition handling will be set to "DELAY". For the FAILURE, ERROR and NOTREADY conditions, this means that further conditions will be ignored until the handling routine returns or until handling is explicitly turned on or off. For the HALT condition, the program will continue executing but the halt signal will be remembered until until the handling routine returns or until handling is explicitly turned on or off. At that time the signal will be handled in an appropriate way. Condition handling with the CALL ON instruction always occurs at clause boundaries. When a condition occurs, it is delayed until the currently executing clause has completed, and then the condition handler is called. At any time after the handling routine is called and before it returns, the CONDITION() builtin function may be used to retrieve information about the condition which was trapped. The information provided by this function is saved across function calls. If a further condition is handled while the handler is still active, this will not affect the information which may be provided to the current handler. When a condition handler is activated, the special variable SIGL is set to the line number of the instruction in which the condition was raised. Also, for conditions ERROR and FAILURE, the special variable RC will hold the return code of the command which caused the condition to be raised. Condition handling will always remain on until turned off with either "CALL OFF condition" or "SIGNAL OFF condition". If an external routine is called, condition handling will be turned off temporarily until the external routine finishes or turns condition handling on. The status of condition handling is saved across function calls. If a subroutine uses a "CALL ON/OFF" or "SIGNAL ON/OFF" instruction, the condition handling within the current routine will be unaffected. A CALL OFF instructions cancels condition handling for a particular condition. If handling is turned off for ERROR, FAILURE or NOTREADY, then the condition will be ignored whenever it occurs. If handling is turned off for HALT then the program will halt when the condition occurs. NOTE: Because calling the handling routine affects the special variable SIGL, this variable can no longer be trusted to remain constant when CALL ON HALT is in effect, since this condition can occur at any time without notice. _________________________________________________________________________ RETURN [value] This statement returns control to the most recent caller, optionally returning a value to the caller. All current DO and SELECT structures are exited and, if appropriate, the current variables are deleted and the caller's variables are reinstated. If the caller was a function call or a CALL statement, the value may be any string which is passed to the caller in the manner described above. If the caller was a function call, the return value must be given or an error results. On return from a condition handler, the result is ignored. If the caller was a shell (that is, no CALL statement or function call is currently active), then the RETURN statement exits from the REXX interpreter. The return value need not be given, but if it is specified it must be an integer, which is returned to the shell as an exit status. _________________________________________________________________________ PROCEDURE PROCEDURE EXPOSE var1 [var2 ...] PROCEDURE HIDE var1 [var2 ...] (LOCAL) The PROCEDURE command is used in an internal function or procedure to hide the caller's variables. The PROCEDURE command on its own hides all the caller's variables and makes sure that on return all the current function's variables are erased. On return from a function containing this instruction, the caller's old variables are reinstated when the current function's have been deleted. The PROCEDURE EXPOSE varlist command is like the form with no arguments except that all the named variables are left visible. These variables will all remain when the RETURN statement deletes all the other variables from the current function. If any of the named variables are not defined, then they will remain undefined until they are assigned a value. This value will then be carried back to the calling procedure. It is not an error to specify a symbol more than once; this will have the same effect as specifying it just once. Simple symbols, stems or compound symbols may be exposed. If a stem is named, then all possible compound symbols starting with that stem will be exposed. BUG: It is not possible to expose a stem and one of its compound symbols at the same time. If a stem is named and one of its compound symbols appears later, then the compound symbol has in effect already been exposed and so the expected results will occur. However, if a stem appears after one of its compound variables, the stem will be ignored without a warning. Any symbol(s) in the list following PROCEDURE EXPOSE may be enclosed in parentheses. In such cases the value of the symbol is used as a list of extra symbols to expose. For example, if the assignment: list = "var1 var2 stem. misc.3" occurred in the calling program, then the instruction: procedure expose test1 (list) test2 will expose the following symbols (in this order): test1 list var1 var2 stem. misc.3 test2 Notice that the symbol inside the parentheses is itself exposed before its value is obtained. LOCAL: The PROCEDURE HIDE varlist command hides only the named variables, leaving the rest visible. On return the hidden variables are deleted, leaving all the others. The action of PROCEDURE HIDE list is identical to that of PROCEDURE EXPOSE <every existing variable except those named>. (in fact what happens is that all existing symbols are exposed and then the named symbols are deleted from the new variable table. This command is therefore quite inefficient and should be used sparingly). The PROCEDURE HIDE statement may not hide individual compound variables. Only stems and simple symbols should be specified, otherwise a syntax error will result. NOTE: This means that variables which are undefined when the PROCEDURE HIDE statement is executed will be deleted on return from the current function. However, if new compound variables are defined having a stem in common with some compound variables which already exist, then the new compound variables will not be deleted on return. NOTE: As in standard REXX, the order in which the symbols are named can have an effect. For example, if i=5 then procedure expose i a.i will expose i and the compound symbol a.5, but procedure expose a.i i will expose the compound symbol a.I and i. This is because the names are processed from left to right, and in the latter case the symbol i is not visible when the name a.i is encountered. The PROCEDURE command will almost invariably be at the beginning of a function or procedure. It may be used in the middle rather than at the beginning, but this is not recommended. In fact the ANSI standard states that PROCEDURE must be the first instruction of a subroutine, if it is present. In any case, an error will result if it is used within an INTERPRET, or a DO, or some other control structure. Example: an improved version of the above factorial program parse arg x say x"!="fact(x) exit fact: procedure /* now we get a different p each time */ parse arg p if p<3 then return p return fact(p-1) * p NOTE: The special variable SIGL must be explicitly exposed if its current value is needed within the procedure. It is set by the CALL instruction or the function call before any PROCEDURE instruction is encountered. _________________________________________________________________________ INTERPRET string This command evaluates the given string and interprets it as if it were part of a real rexx program. The string may contain any commands that the program line containing the INTERPRET command might have executed except that any DO or SELECT control blocks within the string must be complete. That is, the string may not start any new DO or SELECT control blocks to be continued by the main program, and nor can it contain an END, LEAVE, WHEN, etc. corresponding to a control block of the main program. An interpreted command can, however, cause a return from a function. NOTE: Interpreted strings should not contain labels. If they are present then they will be ignored. Example: This program evaluates an expression given on the command line: #!/mclab/imc/sun4/rexx - parse arg x interpret "y="||x say x"="y _________________________________________________________________________ SIGNAL [VALUE] name In this form, the SIGNAL instruction is a primitive form of `goto'. Using it to control program flow in this manner is strongly discouraged. When this command is encountered interpretation jumps to the named label (SIGNAL labels work just like procedure labels - but SIGNAL never invokes another rexx program). If the VALUE keyword is present, or if the name does not start with a symbol or a string constant, then the name is treated as an expression which must evaluate to the name of a label (irrespective of case). All current DO and SELECT structures within the current procedure are terminated by the SIGNAL instruction before the jump is taken. When the SIGNAL instruction is executed, the variable SIGL is set to hold the number of the line at the time of the jump. This can be used in error analysis - as in: if something_is_wrong then signal error ... error: say "Something is wrong at line" sigl or it can be used to type out long texts or help - as in: <lots of argument checking> if something_is_wrong then signal help /* This is a paragraph of help. It is enclosed in comments, so the interpreter ignores it. However the help routine will use the sourceline function to type it out on to the screen. */ ... help: do i=sigl+1 while sourceline(i)~="*/" say sourceline(i) end The SIGNAL VALUE construction is useful for calling procedures with variable names. This can be done as follows: /* procname is set to the name of a procedure */ call jumpto procname,arguments ... jumpto: parse arg jumpname signal value jumpname ... When the named procedure is called, its first argument will be its name, and the subsequent arguments will be those supplied by the caller. The DO and SELECT structures in the calling program are protected from the SIGNAL instruction, since the latter is encountered within procedure `jumpto'. SIGNAL ON condition [NAME symbol] SIGNAL OFF condition These instructions maintain exception handlers for the following contitions: SYNTAX: Any syntax error (for example "Bad arithmetic conversion" or "Unexpected ',' or ')'") which occurs during interpretation. NOVALUE: A variable name is used which has no value. NOTE: This condition is not raised during interpretation of sub-names in compound variables. Hence, if `foo' has no value, then "a=foo+1" will cause a novalue error but "a=abc.foo" will not cause an error unless ABC.'FOO' has no value. Also, the builtin function VALUE() will never raise the NOVALUE condition. HALT: The user has attempted to halt the program, for example by typing Control-C. Signals SIGHUP and SIGTERM also raise the HALT condition. FAILURE: A command to the environment returned a "failure" code. Usually this means a negative return code, but see the section on commands to the environment. ERROR: A command to the environment returned an "error" code. This means a non-zero return code. Note that if "failures" are not being trapped, then "error" will catch failures also. NOTREADY: A function from the REXX I/O model (see the separate section) was unsuccessful because, for example, an input function encountered an end-of-file condition. (These are the same conditions as for CALL ON, with the two extra conditions SYNTAX and NOVALUE). The SIGNAL ON instruction turns on condition handling. Whenever the specified condition occurs, a SIGNAL is made to a handler. If the NAME keyword is specified, then the following symbol is taken as the name of the handler. Otherwise the handler has the same name as the condition. At this point, RC holds the number of the error which caused the jump (except in the case of NOTREADY) and SIGL holds the line number in which the error occurred. The routine in which the SIGNAL ON instruction was encountered becomes the current routine; all internal routines which became active since then are terminated. All DO/SELECT/IF control structures within the current routine are also terminated. The SIGNAL ON instruction is then cancelled, and another SIGNAL ON instruction will be necessary to reinstate handling of this particular condition. At any time after control is passed to the handler, and before the handler causes a return from the current subroutine, the CONDITION() builtin function may be used to retrieve information about the condition which was trapped. A SIGNAL OFF instructions cancels condition handling for a particular condition. If handling is turned off for ERROR, FAILURE, NOTREADY or NOVALUE, then the condition will be ignored whenever it occurs. If handling is turned off for HALT or SYNTAX, then the program will halt when the condition occurs. Condition handling persists from the point of the SIGNAL ON instruction until the current function returns, or until a SIGNAL OFF instruction is executed. If an external routine is called, condition handling will be turned off temporarily until the external routine finishes or turns condition handling on. The status of condition handling is saved across function calls. If a subroutine uses a "SIGNAL ON/OFF" or "CALL ON/OFF" instruction, the condition handling within the current routine will be unaffected. NOTE: The SIGNAL ON SYNTAX command does not trap fatal system errors or the error which is caused when EXIT or RETURN returns a non-integer to the UNIX environment (this is because the latter is, in effect, raised by the environment rather than by the interpreter itself). _________________________________________________________________________ TRACE [symbol] TRACE "string" TRACE VALUE expression The symbol, string constant or expression is evaluated (the VALUE keyword may be omitted if the expression does not start with a symbol or a string constant). It must evaluate to a word consisting of zero or more question marks, followed by an optional letter, followed by an optional string of characters. Each question mark at the start of the string toggles the `interactive tracing' mode (see below), and the following letter, if any, is translated to upper case and must be one of the following: A (All): all clauses are traced before execution C (Commands): all commands to the environment are traced before execution, together with the actual string passed to the environment. If the command results in a non-zero return code, then the return code is traced after execution. E (Error): Any command to the environment resulting in an error (i.e. non-zero return code) is traced after execution, together with the return code F (Failure): Any command to the environment resulting in failure (i.e. negative return code) is traced after execution, together with the return code I (Intermediates): All clauses are traced before execution, and all calculations are traced, including intermediate values evaluated during the calculation. Assignments made by PARSE instructions are also traced. L (Labels): All labels passed during execution are traced N (Normal): the default setting - same as F. O (Off): Nothing is traced, and interactive tracing is also switched off. R (Results): All clauses are traced before execution, and the results from all calculations are traced. Assignments made by PARSE instructions are also traced. If no setting is specified, then interactive tracing is turned off and tracing is set to "N". When clauses are being traced (i.e. A, R or I), when an INTERPRET command is traced, the actual string being interpreted is also traced. When an END command is traced, the source statement to which the END corresponds is also traced. A program may be made to trace itself during execution by signalling it with SIGQUIT (on the Suns this can be done by pressing "control \"). When this signal is received, the tracing mode switches to "?i". If a SIGQUIT is received whilst in interactive tracing mode and if an interruption has already been received but not handled, the program exits immediately (as is the case when SIGQUIT is not handled). This feature exists mainly to stop the interpreter in case of a bug. A program may be made to trace itself when execution starts by using the "-t" commandline flag (see the invocation section for details). Interactive tracing In interactive trace mode, all TRACE instructions passed in the program are ignored and the interpreter will pause after tracing each clause, label, command or return code (as appropriate for the trace setting). The interpreter prompts for input with the string ">trace>". If an empty line is entered (without spaces), execution of the program continues normally until the next event which is traced. If a line of REXX is entered, then that line is interpreted with tracing set to "E". If the line calls a program, then TRACE instructions in that program are ignored. If the line itself uses the TRACE instruction, then the trace setting is altered accordingly and execution of the program will continue after the input line has been interpreted. If the input line does not contain a TRACE instruction, then when it has been interpreted the prompt will reappear for more input. If an error occurs during interpretation of the input line, a message is displayed and the prompt reappears (unless the command executed a TRACE instruction). The error does not cause the program to exit, and no signalling takes place (unless the error occurred in a program which was called by the input line and which contains its own SIGNAL ON xxx command). Commands to the environment within the string will not set the variable RC, but will have non-zero return codes traced. All condition traps are turned off during interpretation of the string. It is possible to make the interpreter change tracing and also prompt for more input by using the built-in TRACE function rather than the TRACE instruction, for example: call trace r sets the `results' tracing mode (whilst keeping interactive mode) without continuing execution of the program. The interactive tracing mode is useful for the following purposes (and others): - single-stepping through a program (use trace ?a) - setting breakpoints (use trace ?l and put a label at the breakpoint) - examining or changing variables during execution. The input line is interpreted in exactly the same way as with the INTERPRET command, and so the same restrictions apply (e.g. DO and END instructions etc must be matched properly). BUG:The following also applies, however: - some of the source information is lost, so any PARSE SOURCE instruction in the line will have the calling method and the calling name replaced by "TRACE" (this does not apply to PARSE SOURCE instructions within programs that may be called by the input line). If the input line transfers control by a SIGNAL instruction, then control is immediately transferred to the target instruction and it is executed before tracing resumes. If the input line contains a RETURN or EXIT instruction, then execution returns to the caller and continues to the end of the current statement. The return may cause a change in the tracing mode, since this is saved across function calls. However, if interactive tracing is still in effect, then tracing will resume at the next instruction. NOTE:If the interpreter has a controlling terminal (that is, "/dev/tty" can be opened when the interpreter initialises), then the trace prompt will be written to the terminal, and input will be read from the terminal. Otherwise, stderr and stdin are used respectively. If an error occurs during a command which was typed in interactive trace mode, then the error message will be written to the terminal. However, all normal input and output use stdin and stdout, while trace output is written to the requested file (see OPTIONS). In particular, if tracing has been redirected, then no trace output will appear on the terminal. Therefore it is not a good idea to redirect tracing when interactive tracing will be used. BUG: Interactive tracing is not recursive, i.e. if, during interactive tracing, a line is entered such as: trace i;say a+b then the tracing of "say a+b" (and other statements following the TRACE instruction) will not be interactive, even though the interactive tracing mode is (in theory) still in operation. TRACE output Each line of trace output is preceded by three characters which identify the type of trace output. Any clause or command traced will be indented according to its logical depth of nesting. Results (or intermediate values) will be indented a further two spaces, and have leading and trailing quotes added. The line numbers of source statements and labels are displayed before the three-character prefix. An interpreted instruction or a command about to be executed will be displayed without a line number. The three-character prefixes are: +++ A trace message (an error message, or the return code from a command) *-* A source statement. This is either the actual text of a statement within a program, or a representation of a statement generated by an INTERPRET statement. *~* The result of evaluating an expression which is either a command to be passed to the environment or the parameter of an INTERPRET instruction. *=* A label. >>> The result of an expression displayed in "trace r", or the value assigned to a variable during parsing or during update of the control variable of a repetitive DO loop. >.> The value `assigned' to a placeholder (dot) during parsing. The following prefixes are used during TRACE I: >V> The contents of a variable >L> a literal (that is, a constant symbol or number, an uninitialised variable, or a string/hex/binary constant) >F> The result of applying a function >P> The result of applying a prefix operator >O> The result of applying a (binary) operator >C> The name of a compound variable (after substitution and before use). The trace setting is saved across function calls, so that if tracing is switched on or off during a function, the previous setting is restored when the function returns. This means that: - if a function is known to work, then "trace off" may be placed at the start. When a program is being traced, tracing is switched off when the function is entered, and back on when the function returns. - if a function is known not to work, then a trace instruction placed at the start of the function will switch tracing on only for the duration of the function call. _________________________________________________________________________ OPTIONS expression The expression is evaluated and broken into blank-delimited words. Each word is examined to see if it is recognised as a valid interpreter option for this implementation. Any word which is not recognised is skipped over, since it probably applies to some other implementation. In REXX/imc, the case of the options is not significant, and options may be abbreviated. The minimum abbreviation for each option is shown in uppercase. Options which require an '=' are only recognised if the '=' sign is present and followed by a valid string. REXX/imc currently recognises the following option: TRACEfile=filespec If "filespec" represents a filename which can be opened for writing, then an information message is written to the standard output and all trace output is redirected to the named file. Otherwise an error message is written to the standard error and tracing remains unchanged. _________________________________________________________________________ ADDRESS [VALUE] [environment] ADDRESS environment command When the REXX interpreter finds a program statement which is not an instruction (as listed above), then it evaluates the whole statement as an expression (if it can), and issues the resulting string to the current environment as a command. The first form of the ADDRESS instruction stated above changes the environment (until the next ADDRESS instruction). If the environment name is given, it may be a symbol (which is translated to upper case, but not substituted by its value) or a string constant, or a string expression preceded by the keyword VALUE. The VALUE may be omitted if the expression does not start with a symbol or a string constant. The current environment is changed to the given string. If no environment name follows the ADDRESS instruction, then the previous environment is made current. For example: address unix /* "UNIX" is current */ address "MY_ENV" /* "MY_ENV" is current */ address /* "UNIX" is current */ address /* "MY_ENV" is current */ The second form of the ADDRESS instruction given above executes a command in a given environment without changing the current environment. The environment name must be a symbol or string constant, and the command may be any string expression. So, if the following line is appended to the previous example: address command "ls -al" the command "ls -al" is executed in environment "COMMAND", while the current environment is still "MY_ENV". Whenever a command is executed, the special variable RC is set to the return code given by the command. If this return code is non-zero, then the command will also cause a FAILURE or ERROR condition to be raised. These conditions are ignored unless trapped by CALL ON or SIGNAL ON. Currently, only two environments are supported: ADDRESS UNIX Each command sent to the "UNIX" environment is executed in a separate Bourne shell. Note that this involves considerable overhead, and moreover no command can make a permanent change to the environment (e.g. "set" and "export" will have no effect). However, it does allow the flexible syntax of the Bourne shell to be used, including piping, I/O redirection, and filename expansion. In this environment, any command which returns a code of 1 will raise the FAILURE condition, as well as any command which returns a negative return code. This is because the Bourne shell always returns 1 when it fails to find the requested command. ADDRESS COMMAND Each command sent to the "COMMAND" environment is tokenised and executed by a primitive shell which is built into the interpreter (in shell.c). This makes for quicker execution of each command, but note that at present the only "meta-characters" which are supported are quotes. That is, enclosing a string in quotes passes it verbatim (i.e. untokenised) as a parameter to a command. In particular, piping, file redirection and filename expansion are not supported. Nor does this shell have any builtin commands (such as cd, set), with the exception of "hash" (see later). For speed of execution, each time a command is executed its path is remembered in a hash table. The hash table statistics may be obtained with the "hash" builtin command, which is similar to that of the Bourne shell (and bash). The command "hash name1 [name2 ...]" will search for each of the given names and add the results to the hash table, but if any of the names is "-r" then the hash table will be cleared. The names are examined from left to right, so "hash cat -r ls" will result in just "/bin/ls" in the hash table. The hash table is also cleared whenever putenv() or value(,,"ENVIRONMENT") is used to change PATH. The command "hash" will print out the list of hash table entries. "hits" represents the number of times a command has been looked up in the table, and "cost" represents the amount of work which was initially carried out in searching along the path for the command. A plus-sign in column 1 indicates that the entry was placed in the same hash bucket as the previous entry; the commands within hash buckets are arranged in alphabetical order. The hash buckets are listed in no particular order. In this environment, an unrecognised command produces return code -3. Any command which produces a negative return code will raise the FAILURE condition. If a command is sent to an unrecognised environment, then return code -3 and a FAILURE condition results. The environment when a program starts up is usually UNIX. The current environment may be found by calling address(), and the environment at startup may be found using "parse source". Here is a simple shell program to demonstrate the use of commands: do i sayn i'>' parse pull command parse upper var command word . if word='EXIT' then exit command if rc!=0 then say "The return code was" rc end i Each command is read from standard input. If the command 'Exit' is received, the shell quits. Otherwise, the command is issued to a Bourne Shell and the return code is checked. NOTE: The program rxstack (in Oxford /mclab/imc/{misc,sun3,sun4}/rxstack) may be used to access the stack while executing a shell command. See the stack section below for details. _________________________________________________________________________ The REXX I/O Model Standard REXX allows files to be accessed using seven the functions charin, charout, chars, linein, lineout, lines, stream. This REXX version has fourteen I/O functions in total; the others remain for backward compatibility but may be removed in future because their functionality is covered by the stream() function. Each I/O function may accept a stream name as a parameter. Usually, the stream name is the path name of a file which will be accessed - though other meanings may be given to streams by the "open", "popen" and "stream" functions. Associated with each currently accessed stream is a read pointer and a write pointer. Characters or lines can be read from the file at the position indicated by the read pointer, or they may be written to the file at the position indicated by the write pointer. In each case the pointer is updated to indicate the new file position after the read or write. The file pointers may be also moved explicitly by various functions. Note that the read and write pointers will in general be different, in contrast to the usual Unix file pointer. Each file is opened by REXX when it is first accessed, and closed when REXX exits. Therefore files need not be opened and closed explicitly, though in this version functions are provided for that purpose. If many files are to be accessed, it is advisable to close files which are no longer needed because otherwise the Unix error "Too many open files" may result. Two kinds of stream exist: persistent and transient. A persistent stream is one which refers to a regular file, whereas a transient stream is any other kind. In particular, ttys and pipes are transient streams. The main difference between the two is that the read and write pointers of a permanent stream may be repositioned, whereas those of a transient stream may not. If a function encounters an I/O error and is unable to perform its function, then it will raise the NOTREADY condition. This condition will be ignored unless it is trapped by SIGNAL ON or CALL ON. However, in all cases it is possible to examine the most recent I/O error using the STREAM() function. The three streams "stdin", "stdout" and "stderr" are already open when REXX starts up. They may be used just as any other files, but they are also accessed by instructions such as "say" and "pull", and by Unix commands. Because of this, REXX/imc only guarantees to be well-behaved if stdin is never written to, and stdout and stderr are never read from. The I/O functions, and their descriptions, follow. Note that no "stream" or "file" name may contain a NUL character (i.e. "00"x). CHARIN([stream] [,[position] [,count]]) If stream is supplied, it is read from, otherwise "stdin" is read. The charin function attempts to read a character from the stream, and returns the result. If count is supplied, then that many characters are read and returned. The length of the result may be less than the number of characters requested if an error occurs. If position is supplied, then the read pointer is seeked to that position (with 1 being the first character of the stream) before reading. If count is zero, then the seek is performed without reading any characters. If count>0 and no characters are read then the NOTREADY condition will be raised. If an interruption (^C) occurs during the read, then characters already read may be lost. NOTE: In order to read single characters from the keyboard, it is necessary to set the terminal into a suitable mode. For example the Unix command "stty cbreak -echo" allows single characters to be read without echoing. This should be reset with "stty -cbreak echo" before the program exits. CHAROUT([stream] [,[string] [,position] ] If stream is supplied, it is written to, otherwise stdout is written to. If the string is supplied, it is written to the stream, otherwise no write is performed. If the position is supplied, the write pointer is set to that position (with 1 being the first character) before the write (if any). If no string and no position are supplied, then all pending output to the stream is flushed, and the write pointer is set to the end of the stream. The result will be the number of characters left unwritten, and if that is non-zero then the NOTREADY condition will be raised. CHARS([stream]) The result will be the number of characters which are immediately available for reading from stream or, if it is omitted, from "stdin". If the stream is not open and does not name a file which can be read, zero will be returned and the NOTREADY condition raised. CLOSE(stream) The named stream is closed and REXX's table of information for that stream is deleted. The result will be the return code from the close system call. NOTE: if stream is one of "stdin" or "stdout" then future input or output operations with "say" and "pull" will fail to work properly. This call is equivalent to STREAM(stream,'c','close) and may be deleted in future releases. FDOPEN(fd [,[mode] [,stream]]) This function is for accessing files which have already been opened by another program and whose file descriptor numbers are known. It should not be used for opening files to which REXX already has access. If mode is supplied, its first character must be one of "r" or "w", meaning that the descriptor is to be opened for reading or read-write respectively. The default is "r". This mode should match the mode of the already-open file descriptor. If the stream argument is supplied, then the given fd will be opened and given that name so that all future references to the fd will call it by the given name. Otherwise, future references to the fd will be by its number. If a stream argument is supplied which names an open stream, that will be closed first. Note that the new stream will be opened on a different descriptor, so in particular this function should not be used to redirect the standard input, output or error. The result from fdopen will be the return code given by the fdopen system call. Example. If this program is called "foo.exec": /* write to file descriptor 3 */ call fdopen 3,"w" call lineout 3,"This is a line of text" then the Bourne Shell command "rexx foo 3>foobar" will write a line of text to the file foobar. This call is equivalent to STREAM(stream,'c','fdopen' [mode] [,fd]) and may be deleted in future releases. FILENO(stream) The result of this function is the file desriptor number associated with the named stream, or -1 if that could not be determined (for example, the stream is not open). This function may be used to pass file descriptors on to shell commands, for instance as in "cat <&7". This call is equivalent to STREAM(stream,'c','fileno') and may be deleted in future releases. FTELL(stream) The result of this function is the current file pointer associated with the given stream (with 1 meaning the beginning), that can be used as a position parameter to the charin or charout calls. If that could not be determined (for example, the stream is a pipe or is not open) then -1 will be returned. NOTE: This is the actual file pointer, not the read or write pointer as stored by REXX (though the answer will probably equal one of those, according as to whether the last operation on the stream was a read or a write). This call is equivalent to STREAM(stream,'c','ftell') and may be deleted in future releases. LINEIN([stream] [,[line] [,count]]) If stream is supplied, it is read from, otherwise "stdin" is read. The linein function attempts to read a line from the stream, and returns the result (with the terminating newline character removed). If count is supplied, it must be zero or one. If zero, then no read is performed, and if one, one line is read. If an error occurs and no characters have been read, then an empty string is returned and the NOTREADY condition is raised. If line is supplied, then the read pointer is seeked to that line number (with 1 being the first line of the stream) before reading. If count is zero, then the seek is performed without reading any characters. If an interruption (^C) occurs during the read, then characters already read may be lost. NOTE: Seeking by line number is very inefficient, because every character of the stream before that line has to be read (unless the current read pointer is at a known line number less than that requested, in which case only every character between the current read position and the required position need be read). LINEOUT([stream] [,[string] [,line]]) If stream is supplied, it is written to, otherwise stdout is written to. If the string is supplied, it is written to the stream and terminated with a newline character, otherwise no write is performed. If line is supplied, the write pointer is set to that line number (with 1 being the first line) before the write (if any). The line must not contain any newline characters, because these will act as line separators in the stream. To write text containing newline characters, please use charout instead. If no string and no line number are supplied, then all pending output to the stream is flushed, and the write pointer is set to the end of the stream. The result will be 1 if the line was not successfully written, in which case the NOTREADY condition will be raised. Otherwise the result will be zero. NOTE: seeking by line number is very inefficient. LINES([stream]) If the named stream, or "stdin" if no stream is named, is a persistent stream (or the name of a regular file), then the number of lines available for reading will be counted and returned. Note that this implies reading every character remaining in the file, and this should be avoided if possible. If the stream is a transient stream, then the result will be "1" if characters may be read immediately from the stream, and "0" otherwise. It is impossible to calculate the exact number of lines in this case. If the stream is not already open and does not name a file which can be read, then zero will be returned and the NOTREADY condition raised. OPEN(file [,[mode] [,stream]]) The file specified is opened, if possible, and the error code from the system call is returned. If mode is omitted, then the file is opened for reading only, otherwise the first character of the mode must be "r" (to open for reading), "w" (to open for read/write, with the file being created or truncated initially), or "a" (to append, i.e. open for read/write with the write pointer at the end of any existing data in the file initially). This function will not raise the NOTREADY condition, nor will it record any error for STREAM() - the stream will remain unopened (or "UNKNOWN") if the open fails. The return code from the call should be checked to see whether an error occurred. If the stream argument is supplied, then any future reference to the open file will use this as the stream name - otherwise the filename (exactly as specified in the open function call) will be used. If a stream argument is supplied which already refers to an open file, then that will be closed and the new file will be opened on the same descriptor. The standard input, output or error may be redirected by calling open with 'stdin', 'stdout' or 'stderr' as the stream argument. This call is equivalent to STREAM(stream,'c','open' [mode][,file]) and may be deleted in future releases. PCLOSE(stream) This function must be used to close any stream which was opened by the popen function. The result will be the error code from the pclose system call, which will in turn be the exit code of the command being run at the other end of the pipe if the pipe was closed successfully or -1 if not. A result of -1 may mean that the given stream was not opened with popen. This function will not raise the NOTREADY condition, nor will it record any error for STREAM(). This call is equivalent to STREAM(stream,'c','pclose') and may be deleted in future releases. POPEN(command [,[mode] [,stream]]) A Bourne Shell is started off in the background to run the given command with a one-way pipe leading from or to it. If the mode is omitted, or starts with the letter R, then the output of the command may be read from the pipe. If a mode starting with the letter W is given, then the input of the command may be written down the pipe. The return value from popen will be zero if the pipe was opened successfully, or an error number if not. Note that the pipe may still be opened successfully even if the command can not be executed: it is the Bourne Shell's job to report that the command can not be executed. The return code from the shell can be obtained with the pclose function. This function will not raise the NOTREADY condition, nor will it record any error for STREAM(). If the stream argument is supplied, then any future reference to the pipe will use this as the stream name - otherwise the command in full will be used. If a stream argument is supplied which already refers to an open stream, then that will be closed after the pipe has been successfully opened. This means that the pipe will be opened on a different descriptor, and the popen function should not be used to redirect the standard input, output or error. The pipe should be closed with the pclose function so that the shell process may be removed from the process table. If that is not done, then defunct processes will remain until REXX exits. This may be acceptable for a small number of popen calls, but not if the REXX program calls popen many times or is long-lived. Example: the following program outputs in hex, using an "od" process: output= "/bin/od -x" call popen output,"w" call lineout output,"This is some sample output" call pclose output This call is equivalent to STREAM(stream,'c','popen' [mode][,command]) and may be deleted in future releases. STREAM(stream[,[option][,command]]) This function provides miscellaneous operations on the named stream. The first character of the option must be "C", "D" or "S" (in upper or lower case), if the option is given. If the option is omitted, then "S" is assumed. The command parameter must be given if and only if the option is "C". Option "S" The function returns the status of the stream as one of the following strings: "READY" - the stream is ready for input or output. "NOTREADY" - the stream is not ready; usually this indicates that the end of the file was reached. "ERROR" - an I/O error has occurred. "UNKNOWN" - the stream has not been accessed. Option "D" The function returns a description of the stream's status. This will be "Ready", "Unknown", or the text of an error which has occurred. This option may be used after a NOTREADY condition is trapped, to find out what happened to the stream. Option "C" The function executes the given command on the stream and returns a result depending on the command. Valid commands in REXX/imc follow. All command names and mode parameters may be given in mixed case, and wherever a comma appears in the command, a space is acceptable as long as the parameter before it is not omitted. For example, stream('file','c','Open R /tmp/testfile') is a valid call to this function. close - the named stream is closed and the return value from the system call is returned. See CLOSE() for details. fdopen [mode][,number] - if the number is given, it is used as a numeric file descriptor and opened on the given stream. Otherwise, the given stream is taken to be a numeric file descriptor and opened. If the mode is omitted, "r" is assumed. The return value from the system call is returned. See FDOPEN() for details. fileno - the file descriptor corresponding to the given stream is returned. See FILENO() for details. flush - the named stream is flushed. This is similar to calling charout(stream). ftell - the file pointer of the given stream is returned. See FTELL() for details. open [mode][,file] - if the file name is supplied, it is opened on the given stream. Otherwise, the given stream is taken to be a file name and opened. If the mode is omitted, "r" is assumed. The return value from the system call is returned. See OPEN() for details. pclose - the stream, which must have been opened by "popen", is closed. The return value from the system call is returned. See PCLOSE() for details. popen [mode][,command] - if the command is supplied, a Bourne shell is started up to execute it. Otherwise, the given stream name is assumed to be a command and the shell is started up to execute that. A pipe is opened from the shell to the given stream. If the mode is omitted, "r" is assumed. The return value from the system call is returned. See POPEN() for details. _________________________________________________________________________ The REXX Stack The REXX stack is implemented by a stack process, with which the interpreter communicates by means of a socket. The PUSH, QUEUE, and PULL instructions and the QUEUED() function all communicate with the stack process. If a stack exists, then the standalone program rxstack may be used to stack or retrieve data. This can be used to communicate to rexx the output of a command (for instance "ls -al | rxstack") or to input data from rexx (for instance "rxstack -print > /tmp/file"). The invocation syntax of this program is: rxstack [-fifo|-lifo] [-print|-pop|-peek|-drop|-num|-string "data"] The meaning of these flags is as follows: -fifo stack in FIFO order (the default) -lifo stack in LIFO order -print empty the stack, outputting each item on standard output -pop pop one item and output on standard output -peek output the first item on standard output without deleting it -drop discard one item -num output the number of items currently stacked on standard output in decimal, followed by newline character -string interpret the next argument as a literal string to be stacked If none of the above flags (except -fifo or -lifo) is specified, then each line of standard input is stacked until an EOF is received. Each stack item may comtain arbitrary characters, including newline characters, but when rxstack takes input from standard input, all newline characters are taken to be item separators and are deleted before each item is stacked. Similarly, when rxstack outputs stack items each item is followed by a newline character. The name of the socket used for communication is stored in the environment variable RXSTACK. It is assumed that a stack exists if and only if this variable exists. Multiple processes may share the same stack but multiple users may not usually share one stack because the sockets for each user are kept in a separate protected directory belonging to that user. When REXX is invoked, if no stack exists then one is created, and is destroyed when REXX exits. If a stack exists then REXX uses that stack. The program rxque may be used to create a stack process independently of REXX (for instance, so that REXX need not create one on startup, or so that stack data may persist across invocations of REXX). This is done by the program rxque. It may be invoked in three different ways: rxque starts a stack process in the background and outputs two environment variables to stdout in the format RXSTACK=<name> RXSTACKPROC=<number> where RXSTACKPROC is the process number of the stack, which must be killed when the stack is no longer needed. To avoid unwanted processes being left around when errors occur, rxque will terminate itself if it finds that its parent process no longer exists when it has been sleeping for five minutes without communication. This output can either be parsed by a controlling program or used directly by a shell, for instance by: eval `rxque`;export RXSTACK RXSTACKPROC rxque -csh is similar to the above but outputs two setenv commands in a format acceptable for the c-shell, so that eval `rxque -csh` will set the environment variables correctly in the c-shell. rxque <filename> starts a stack process in the background which uses <filename> as the communication socket. This file will be deleted if it exists, before the socket with that name is opened. The process number of the stack process will be output to stdout, followed by a newline. For instance: % eval `rxque -csh` % ls -al | rxstack -lifo % rxstack -num 45 % rxstack -print [many lines deleted] drwxr-xr-x 13 imc 1536 Oct 28 16:56 .. drwx------ 5 imc 1024 Oct 28 13:12 . total 194 % kill $RXSTACKPROC % unsetenv RXSTACK % rxstack RX Stack not found _________________________________________________________________________ Error Messages As far as is possible, this interpreter conforms to the standard numbering system for error messages. Messages which may be produced by this interpreter are as follows (explanations are omitted when the meaning is obvious): Failure returns (negative) -3 Error loading program A message indicating the reason will usually be displayed immediately before this message. -1 Initialisation error A failure in some essential service, such as not being able to start up the stack process. Alternatively, some error occurred while processing the commandline arguments (in which case an explanation follows the message text). Standard REXX errors (1-50) 4 Program interrupted Control-C has been typed, or a SIGHUP or SIGTERM signal has been received. 5 Machine storage exhausted 6 Unmatched '/*' or quote (this is reported as the program is loaded, before execution. The line number given corresponds to the start of the string or comment which is unterminated. Alternatively, the error may occur during an INTERPRET instruction, in which case the INTERPRET instruction itself is named. This also applies to errors 13 and 37). 7 Expected WHEN/OTHERWISE Either a SELECT is not followed immediately by a WHEN, or the end of the SELECT structure has been reached, no condition was true, and no OTHERWISE clause is present. 8 Unexpected THEN/ELSE 9 Unexpected WHEN/OTHERWISE 10 Unexpected or unmatched END 13 Invalid character in program: [char] The only characters which are allowed in program text (excluding comments and string constants) are spaces, tabs, newlines, the alphanumerics (A-Z, a-z, 0-9) and the symbols: @#.?!_$|&*()-+=^\'";:<,>%/ (see also error 6) 14 Incomplete DO/SELECT/IF An END is probably missing. 15 Invalid binary or hexadecimal string 16 Label not found: [label] The target of a SIGNAL (whether explicit or caused by a trap) is missing. 17 Unexpected PROCEDURE The PROCEDURE instruction should only be placed directly after the entry point of a function. 18 Expected THEN 19 String or symbol expected A string or symbol was expected (e.g. after SIGNAL or NUMERIC FORM) but was missing or invalid. 20 Symbol expected A symbol was expected (e.g. after PARSE VAR or, optionally, after LEAVE or ITERATE) but was missing or invalid. 21 Invalid data on end of clause Extra characters were found when the interpreter expected a line end or a semicolon. In the special case of the END instruction, the symbol (or SELECT) appearing after the END did not match up with the beginning of the structure being ended. 24 Invalid TRACE request 25 Invalid subkeyword found In an instruction such as NUMERIC which requires a subkeyword (e.g. NUMERIC DIGITS, etc), that subkeyword was missing or invalid. 26 Invalid whole number A function call or an instruction required an integer expression, but either a non-integer or an out-of-range number was supplied. The magnitude of a whole number should not exceed 1999999999. 27 Invalid DO syntax 28 Invalid LEAVE or ITERATE A symbol specified after LEAVE or ITERATE was either invalid or did not correspond to an active loop, or there is no loop currently active. 30 Symbol > [nnn] characters A variable name exceeded the implementation limit. 31 Name starts with number or '.' The name in this case may be a label name (in which case the error is reported as the program is read in), or a symbol which is being given a value in an attempted assignment. 35 Invalid expression A syntax error occurred during the evaluation of an expression. This error also sometimes results when an expression is missing. 36 Unmatched '(' 37 Unexpected ',' or ')' When reported during loading or before interpreting a string (see error 6), this means that a comma occurred at the end of a line which has no successor. At other times, it means that either an unmatched right parenthesis was found or that a comma was found in an inappropriate position (such as in SAY 1,2) 38 Invalid template A PARSE instruction has invalid syntax. 39 Evaluation stack overflow (> [nn] pending operations) An expression was too complex to evaluate. This usually only occurs if there is a large number of successive prefix operations, such as in: say ++++++++++++++++++++++++++++1. 40 Incorrect call to routine A call to a function or subroutine specified the wrong number of parameters, or missed out a mandatory parameter, or supplied an inappropriate parameter for the function. 41 Bad arithmetic conversion An arithmetic operator was used on a string which is not a number. 42 Arithmetic overflow or underflow 43 Routine not found: [name] 44 Function did not return data 48 Failure in system service This indicates either that a communication error occurred whilst dealing with the stack, or that an error occurred whilst trying to load a ".rxfn" file to call an external function. 49 Implementation error The REXX interpreter has discovered a bug in itself, since some internal structure is inconsistent. Naturally, you will never see this message. ;-) Implementation-defined errors (80-99) 80 No-value error This is the value to which the special variable rc is set when a SIGNAL ON NOVALUE trap is activated. 81 Use of an un-implemented feature! 82 Syntax error A syntax error has been discovered which cannot be described by any of the other messages (This message should never appear except when a LOCAL feature is being used). 83 Label ends with '.' (this error is reported as the program is read in) Labels ending with '.' are disallowed since a program containing such a label may be unaware that foo.(3) is not a call to the function "foo." but a reference to a compound symbol. 84 Too many arguments (> [nn]) A call to a function or subroutine specified too many actual parameters for the interpreter to handle. 85 ERROR condition occurred This code is used internally to when a "SIGNAL ON ERROR" occurs. You may see this message if the signal handler does not exist. 86 FAILURE condition occurred This code is used internally to when a "SIGNAL ON ERROR" occurs. You may see this message if the signal handler does not exist. 88 Unexpected '*/' This combination of symbols would usually cause an "Invalid expression" error, but it is singled out because the usual reason for this error is that a begin-comment delimiter has been omitted or mistyped. This error is reported as the program is read in. Unix system errors (101-198) These are the error messages which may result from a call to stream() with the "Describe" option. They are defined by the Unix run-time library, and include such messages as "Permission denied" and "No such file or directory". The number of the message is just 100 plus its usual value in Unix. Other I/O errors (100,199-210) These are the error messages which may result from a call to stream() with the "Describe" option and which are provided by the interpreter rather than by the system. 100 Unknown error occurred during I/O An error occurred, but the system call failed to set errno to a meaningful value. 199 End of file 200 File position was out of bounds REXX level 4.00 does not allow you to use charin or linein to point to a non-existent character, or to use charout or lineout to point more than one byte beyond the end of file. If you attempt this, then NOTREADY will be raised with this error. 201 Reposition attempted on transient stream REXX does not allow you to reposition a stream unless it is a persistent stream (i.e., a regular file). Repositioning on a pipe or tty is not allowed and will raise NOTREADY with this error. 202 Write attempted on a read-only stream This error occurs if you try to write to stdin, or to any stream which was opened via the stream function without a name in read mode (for instance, with popen or fdopen). _________________________________________________________________________