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MAWK(1) USER COMMANDS MAWK(1) NAME mawk - pattern scanning and text processing language SYNOPSIS mawk [-W _o_p_t_i_o_n] [-F _v_a_l_u_e] [-v _v_a_r=_v_a_l_u_e] [--] 'program text' [file ...] mawk [-W _o_p_t_i_o_n] [-F _v_a_l_u_e] [-v _v_a_r=_v_a_l_u_e] [-f _p_r_o_g_r_a_m-_f_i_l_e] [--] [file ...] DESCRIPTION mawk is an interpreter for the AWK Programming Language. The AWK language is useful for manipulation of data files, text retrieval and processing, and for prototyping and experimenting with algorithms. mawk is a _n_e_w _a_w_k meaning it implements the AWK language as defined in Aho, Kernighan and Weinberger, _T_h_e _A_W_K _P_r_o_g_r_a_m_m_i_n_g _L_a_n_g_u_a_g_e, Addison-Wesley Publishing, 1988. (Hereafter referred to as the AWK book.) mawk conforms to the Posix 1003.2 (draft 11.2) definition of the AWK language which contains a few features not described in the AWK book, and mawk provides a small number of exten- sions. An AWK program is a sequence of _p_a_t_t_e_r_n {_a_c_t_i_o_n} pairs and function definitions. Short programs are entered on the command line usually enclosed in ' ' to avoid shell interpretation. Longer programs can be read in from a file with the -f option. Data input is read from the list of files on the command line or from standard input when the list is empty. The input is broken into records as deter- mined by the record separator variable, RS. Initially, RS = "\n" and records are synonymous with lines. Each record is compared against each _p_a_t_t_e_r_n and if it matches, the program text for {_a_c_t_i_o_n} is executed. OPTIONS -F _v_a_l_u_e sets the field separator, FS, to _v_a_l_u_e. -f _f_i_l_e Program text is read from _f_i_l_e instead of from the command line. Multiple -f options are allowed. -v _v_a_r=_v_a_l_u_e assigns _v_a_l_u_e to program variable _v_a_r. -- indicates the unambiguous end of options. Version 1.1 Last change: Jan 22 1992 1 MAWK(1) USER COMMANDS MAWK(1) The above options will be available with any Posix compati- ble implementation of AWK, and implementation specific options are prefaced with -W. mawk provides three: -W version mawk writes its version and copyright to stdout and compiled limits to stderr and exits 0. -W dump writes an assembler like listing of the inter- nal representation of the program to stderr. -W sprintf=_n_u_m adjusts the size of mawk's internal sprintf buffer to _n_u_m bytes. More than rare use of this option indicates mawk should be recom- piled. -W posix_space forces mawk not to consider '\n' to be space. THE AWK LANGUAGE 1. Program structure An AWK program is a sequence of _p_a_t_t_e_r_n {_a_c_t_i_o_n} pairs and user function definitions. A pattern can be: BEGIN END expression expression , expression One, but not both, of _p_a_t_t_e_r_n {_a_c_t_i_o_n} can be omitted. If {_a_c_t_i_o_n} is omitted it is implicitly { print }. If _p_a_t_t_e_r_n is omitted, then it is implicitly matched. BEGIN and END patterns require an action. Statements are terminated by newlines, semi-colons or both. Groups of statements such as actions or loop bodies are blocked via { ... } as in C. The last statement in a block doesn't need a terminator. Blank lines have no meaning; an empty statement is terminated with a semi-colon. Long state- ments can be continued with a backslash, \. A statement can be broken without a backslash after a comma, left brace, &&, ||, do, else, the right parenthesis of an if, while or for statement, and the right parenthesis of a function defini- tion. A comment starts with # and extends to, but does not include the end of line. The following statements control program flow inside blocks. Version 1.1 Last change: Jan 22 1992 2 MAWK(1) USER COMMANDS MAWK(1) if ( _e_x_p_r ) _s_t_a_t_e_m_e_n_t if ( _e_x_p_r ) _s_t_a_t_e_m_e_n_t else _s_t_a_t_e_m_e_n_t while ( _e_x_p_r ) _s_t_a_t_e_m_e_n_t do _s_t_a_t_e_m_e_n_t while ( _e_x_p_r ) for ( _o_p_t__e_x_p_r ; _o_p_t__e_x_p_r ; _o_p_t__e_x_p_r ) _s_t_a_t_e_m_e_n_t for ( _v_a_r in _a_r_r_a_y ) _s_t_a_t_e_m_e_n_t continue break 2. Data types, conversion and comparison There are two basic data types, numeric and string. Numeric constants can be integer like -2, decimal like 1.08, or in scientific notation like -1.1e4 or .28E-3. All numbers are represented internally and all computations are done in floating point arithmetic. So for example, the expression 0.2e2 == 20 is true and true is represented as 1.0. String constants are enclosed in double quotes. "This is a string with a newline at the end.\n" Strings can be continued across a line by escaping (\) the newline. The following escape sequences are recognized. \\ \ \" " \a alert, ascii 7 \b backspace, ascii 8 \t tab, ascii 9 \n newline, ascii 10 \v vertical tab, ascii 11 \f formfeed, ascii 12 \r carriage return, ascii 13 \ddd 1, 2 or 3 octal digits for ascii ddd \xhh 1 or 2 hex digits for ascii hh If you escape any other character \c, you get \c, i.e., mawk ignores the escape. There are really three basic data types; the third is _n_u_m_b_e_r _a_n_d _s_t_r_i_n_g which has both a numeric value and a string value at the same time. User defined variables come into existence when first referenced and are initialized to _n_u_l_l, a number and string value which has numeric value 0 and string value "". Non-trivial number and string typed data Version 1.1 Last change: Jan 22 1992 3 MAWK(1) USER COMMANDS MAWK(1) come from input and are typically stored in fields. (See section 4). The type of an expression is determined by its context and automatic type conversion occurs if needed. For example, to evaluate the statements y = x + 2 ; z = x "hello" The value stored in variable y will be typed numeric. If x is not numeric, the value taken from x is converted to numeric before it is added to 2 and stored in y. The value stored in variable z will be typed string, and the value of x will be converted to string if necessary and concatenated with "hello". (Of course, the value and type stored in x is not changed by any conversions.) A string expression is con- verted to numeric using its longest numeric prefix as with _a_t_o_f(3). A numeric expression is converted to string by replacing _e_x_p_r with sprintf(CONVFMT, _e_x_p_r), unless _e_x_p_r can be represented on the host machine as an exact integer then it is converted to sprintf("%d", _e_x_p_r). Sprintf() is an AWK built-in that duplicates the functionality of _s_p_r_i_n_t_f(3), and CONVFMT is a built-in variable used for internal conver- sion from number to string and initialized to "%.6g". Explicit type conversions can be forced, _e_x_p_r "" is string and _e_x_p_r+0 is numeric. To evaluate, _e_x_p_r1 rel-op _e_x_p_r2, if both operands are numeric or number and string then the comparison is numeric; if both operands are string the comparison is string. If exactly one operand is string and after trimming spaces and tabs from the front and back the remaining string is entirely numeric in form, then the string is converted to number and the comparison is numeric; otherwise, the numeric operand is converted to string and the comparison is string. The result of a comparison is numeric, 0 or 1. In boolean contexts such as, if ( _e_x_p_r ) _s_t_a_t_e_m_e_n_t, a string expression evaluates true if and only if it is not the empty string ""; numeric values if and only if not numerically zero. 3. Regular expressions In the AWK language, records, fields and strings are often tested for matching a _r_e_g_u_l_a_r _e_x_p_r_e_s_s_i_o_n. Regular expres- sions are enclosed in slashes, and _e_x_p_r ~ /_r/ is an AWK expression that evaluates to 1 if _e_x_p_r "matches" _r, which means a substring of _e_x_p_r is in the set of strings defined by _r. With no match the expression evaluates to 0; Version 1.1 Last change: Jan 22 1992 4 MAWK(1) USER COMMANDS MAWK(1) replacing ~ with the "not match" operator, !~ , reverses the meaning. As pattern-action pairs, /_r/ { _a_c_t_i_o_n } and $0 ~ /_r/ { _a_c_t_i_o_n } are the same, and for each input record that matches _r, _a_c_t_i_o_n is executed. In fact, /_r/ is an AWK expression that is equivalent to ($0 ~ /_r/) anywhere except when on the right side of a match operator or passed as an argument to a built-in function that expects a regular expression argu- ment. AWK uses extended regular expressions as with _e_g_r_e_p(1). The regular expression metacharacters, i.e., those with special meaning in regular expressions are ^ $ . [ ] | ( ) * + ? Regular expressions are built up from characters as follows: _c matches any non-metacharacter _c. \_c matches a character defined by the same escape sequences used in string constants or the literal character _c if \_c is not an escape sequence. . matches any character (including newline). ^ matches the front of a string. $ matches the back of a string. [c1c2c3...] matches any character in the class c1c2c3... . An interval of characters is denoted c1-c2 inside a class [...]. [^c1c2c3...] matches any character not in the class c1c2c3... Regular expressions are built up from other regular expres- sions as follows: _r1_r2 matches _r1 followed immediately by _r2 (concatena- tion). _r1 | _r2 matches _r1 or _r2 (alternation). _r* matches _r repeated zero or more times. _r+ matches _r repeated one or more times. Version 1.1 Last change: Jan 22 1992 5 MAWK(1) USER COMMANDS MAWK(1) _r? matches _r zero or once. (_r) matches _r, providing grouping. The increasing precedence of operators is alternation, con- catenation and unary (*, + or ?). For example, /^[_a-zA-Z][_a-zA-Z0-9]*$/ and /^[-+]?([0-9]+\.?|\.[0-9])[0-9]*([eE][-+]?[0-9]+)?$/ are matched by AWK identifiers and AWK numeric constants respectively. Note that . has to be escaped to be recog- nized as a decimal point, and that metacharacters are not special inside character classes. Any expression can be used on the right hand side of the ~ or !~ operators or passed to a built-in that expects a regu- lar expression. If needed, it is converted to string, and then interpreted as a regular expression. For example, BEGIN { identifier = "[_a-zA-Z][_a-zA-Z0-9]*" } $0 ~ "^" identifier prints all lines that start with an AWK identifier. mawk recognizes the empty regular expression, //, which matches the empty string and hence is matched by any string at the front, back and between every character. For exam- ple, echo abc | mawk { gsub(//, "X") ; print } XaXbXcX 4. Records and fields Records are read in one at a time, and stored in the _f_i_e_l_d variable $0. The record is split into _f_i_e_l_d_s which are stored in $1, $2, ..., $NF. The built-in variable NF is set to the number of fields, and NR and FNR are incremented by 1. Fields above $NF are set to "". Assignment to $0 causes the fields and NF to be recomputed. Assignment to NF or to a field causes $0 to be reconstructed by concatenating the $i's separated by OFS. Assignment to a field with index greater than NF, increases NF and causes $0 to be reconstructed. Data input stored in fields is string, unless the entire field has numeric form and then the type is number and Version 1.1 Last change: Jan 22 1992 6 MAWK(1) USER COMMANDS MAWK(1) string. For example, echo 24 24E | mawk '{ print($1>100, $1>"100", $2>100, $2>"100") }' 0 0 1 1 $0 and $2 are string and $1 is number and string. The first and second comparisons are numeric and the last two are string. In the second "100" is converted to 100, and in the third 100 is converted to "100". 5. Expressions and operators The expression syntax is similar to C. Primary expressions are numeric constants, string constants, variables, fields, arrays and functions. The identifier for a variable, array or function can be a sequence of letters, digits and under- scores, that does not start with a digit. Variables are not declared; they exist when first referenced and are initial- ized to _n_u_l_l. New expressions are composed with the following operators in order of increasing precedence. _a_s_s_i_g_n_m_e_n_t = += -= *= /= %= ^= _c_o_n_d_i_t_i_o_n_a_l ? : _l_o_g_i_c_a_l _o_r || _l_o_g_i_c_a_l _a_n_d && _a_r_r_a_y _m_e_m_b_e_r_s_h_i_p in _m_a_t_c_h_i_n_g ~ !~ _r_e_l_a_t_i_o_n_a_l < > <= >= == != _c_o_n_c_a_t_e_n_a_t_i_o_n (no explicit operator) _a_d_d _o_p_s + - _m_u_l _o_p_s * / % _u_n_a_r_y + - _l_o_g_i_c_a_l _n_o_t ! _e_x_p_o_n_e_n_t_i_a_t_i_o_n ^ _i_n_c _a_n_d _d_e_c ++ -- (both post and pre) _f_i_e_l_d $ Assignment, conditional and exponentiation associate right to left; the other operators associate left to right. Any expression can be parenthesized. 6. Arrays Awk provides one-dimensional arrays. Array elements are expressed as _a_r_r_a_y[_e_x_p_r]. _E_x_p_r is internally converted to string type, so, for example, A[1] and A["1"] are the same element and the actual index is "1". Arrays indexed by strings are called associative arrays. Initially an array is empty; elements exist when first accessed. An expres- sion, _e_x_p_r in _a_r_r_a_y evaluates to 1 if _a_r_r_a_y[_e_x_p_r] exists, else to 0. Version 1.1 Last change: Jan 22 1992 7 MAWK(1) USER COMMANDS MAWK(1) There is a form of the for statement that loops over each index of an array. for ( _v_a_r in _a_r_r_a_y ) _s_t_a_t_e_m_e_n_t sets _v_a_r to each index of _a_r_r_a_y and executes _s_t_a_t_e_m_e_n_t. The order that _v_a_r transverses the indices of _a_r_r_a_y is not defined. The statement, delete _a_r_r_a_y[_e_x_p_r], causes _a_r_r_a_y[_e_x_p_r] not to exist. Multidimensional arrays are synthesized with concatenation using the built-in variable SUBSEP. _a_r_r_a_y[_e_x_p_r1,_e_x_p_r2] is equivalent to _a_r_r_a_y[_e_x_p_r1 SUBSEP _e_x_p_r2]. Testing for a mul- tidimensional element uses a parenthesized index, such as if ( (i, j) in A ) print A[i, j] 7. Builtin-variables The following variables are built-in and initialized before program execution. ARGC number of command line arguments. ARGV array of command line arguments, 0..ARGC-1. CONVFMT format for internal conversion of numbers to string, initially = "%.6g". ENVIRON array indexed by environment variables. An environment string, _v_a_r=_v_a_l_u_e is stored as ENVIRON[_v_a_r] = _v_a_l_u_e. FILENAME name of the current input file. FNR current record number in FILENAME. FS splits records into fields as a regular expression. NF number of fields in the current record. NR current record number in the total input stream. OFMT format for printing numbers; initially = "%.6g". OFS inserted between fields on output, initially = " ". Version 1.1 Last change: Jan 22 1992 8 MAWK(1) USER COMMANDS MAWK(1) ORS terminates each record on output, initially = "\n". RLENGTH length set by the last call to the built-in function, match(). RS input record separator, initially = "\n". RSTART index set by the last call to match(). SUBSEP used to build multiple array subscripts, ini- tially = "\034". 8. Built-in functions String functions gsub(_r,_s,_t) gsub(_r,_s) Global substitution, every match of regular expression _r in variable _t is replaced by string _s. The number of replacements is returned. If _t is omitted, $0 is used. An & in the replacement string _s is replaced by the matched substring of _t. \& puts a literal & in the replacement string. index(_s,_t) If _t is a substring of _s, then the position where _t starts is returned, else 0 is returned. The first character of _s is in position 1. length(_s) length() Returns the length of string _s; without an argu- ment, returns the length of $0. match(_s,_r) Returns the index of the first longest match of regular expression _r in string _s. Returns 0 if no match. As a side effect, RSTART is set to the return value. RLENGTH is set to the length of the match or -1 if no match. If the empty string is matched, RLENGTH is set to 0, and 1 is returned if the match is at the front, and length(_s)+1 is returned if the match is at the back. split(_s,_A,_r) split(_s,_A) String _s is split into fields by regular expres- sion _r and the fields are loaded into array _A. The number of fields is returned. See section 11 below for more detail. If _r is omitted, FS is used. sprintf(_f_o_r_m_a_t,_e_x_p_r-_l_i_s_t) Returns a string constructed from _e_x_p_r-_l_i_s_t Version 1.1 Last change: Jan 22 1992 9 MAWK(1) USER COMMANDS MAWK(1) according to _f_o_r_m_a_t. See the description of printf() below. sub(_r,_s,_t) sub(_r,_s) Single substitution, same as gsub() except at most one substitution. substr(_s,_i,_n) substr(_s,_i) Returns the substring of string _s, starting at index _i, of length _n. If _n is omitted, the suffix of _s, starting at _i is returned. tolower(_s) Returns a copy of _s with all upper case characters converted to lower case. toupper(_s) Returns a copy of _s with all lower case characters converted to upper case. Arithmetic functions atan2(_y,_x) Arctan of _y/_x between -pi and pi. cos(_x) Cosine function, _x in radians. exp(_x) Exponential function. int(_x) Returns _x truncated towards zero. log(_x) Natural logarithm. rand() Returns a random number between zero and one. sin(_x) Sine function, _x in radians. sqrt(_x) Returns square root of _x. srand(_e_x_p_r) srand() Seeds the random number generator, using the clock if _e_x_p_r is omitted, and returns the value of the previous seed. mawk seeds the random number gen- erator from the clock at startup so there is no real need to call srand(). Srand(_e_x_p_r) is useful for repeating pseudo random sequences. 9. Input and output There are two output statements, print and printf. print writes $0 ORS to standard output. Version 1.1 Last change: Jan 22 1992 10 MAWK(1) USER COMMANDS MAWK(1) print _e_x_p_r1, _e_x_p_r2, ..., _e_x_p_rn writes _e_x_p_r1 OFS _e_x_p_r2 OFS ... _e_x_p_rn ORS to stan- dard output. Numeric expressions are converted to string with OFMT. printf _f_o_r_m_a_t, _e_x_p_r-_l_i_s_t duplicates the printf C library function writing to standard output. The complete ANSI C format specifications are recognized with conversions %c, %d, %e, %E, %f, %g, %G, %i, %o, %s, %u, %x, %X and %%, and conversion qualifiers h and l. The argument list to print or printf can optionally be enclosed in parentheses. Print formats numbers using OFMT or "%d" for exact integers. "%c" with a numeric argument prints the corresponding 8 bit character, with a string argument it prints the first character of the string. The output of print and printf can be redirected to a file or command by appending > _f_i_l_e, >> _f_i_l_e or | _c_o_m_m_a_n_d to the end of the print statement. Redirection opens _f_i_l_e or _c_o_m_m_a_n_d only once, subsequent redirections append to the already open stream. By convention, mawk associates the filename "/dev/stderr" with stderr which allows print and printf to be redirected to stderr. The input function getline has the following variations. getline reads into $0, updates the fields, NF, NR and FNR. getline < _f_i_l_e reads into $0 from _f_i_l_e, updates the fields and NF. getline _v_a_r reads the next record into _v_a_r, updates NR and FNR. getline _v_a_r < _f_i_l_e reads the next record of _f_i_l_e into _v_a_r. _c_o_m_m_a_n_d | getline pipes a record from _c_o_m_m_a_n_d into $0 and updates the fields and NF. _c_o_m_m_a_n_d | getline _v_a_r pipes a record from _c_o_m_m_a_n_d into _v_a_r. Getline returns 0 on end-of-file, -1 on error, otherwise 1. Commands on the end of pipes are executed by /bin/sh. Version 1.1 Last change: Jan 22 1992 11 MAWK(1) USER COMMANDS MAWK(1) The function close(_e_x_p_r) closes the file or pipe associated with _e_x_p_r. Close returns 0 if _e_x_p_r is an open file, the exit status if _e_x_p_r is a piped command, and -1 otherwise. Close() is used to reread a file or command, make sure the other end of an output pipe is finished or conserve file resources. The function system(_e_x_p_r) uses /bin/sh to execute _e_x_p_r and returns the exit status of the command _e_x_p_r. Changes made to the ENVIRON array are not passed to commands executed with system or pipes. 10. User defined functions The syntax for a user defined function is function name( _a_r_g_s ) { _s_t_a_t_e_m_e_n_t_s } The function body can contain a return statement return _o_p_t__e_x_p_r A return statement is not required. Function calls may be nested or recursive. Functions are passed expressions by value and arrays by reference. Extra arguments serve as local variables and are initialized to _n_u_l_l. For example, csplit(_s,_A) puts each character of _s into array _A and returns the length of _s. function csplit(s, A, n, i) { n = length(s) for( i = 1 ; i <= n ; i++ ) A[i] = substr(s, i, 1) return n } Putting extra space between passed arguments and local vari- ables is conventional. Functions can be referenced before they are defined, but the function name and the '(' of the arguments must touch to avoid confusion with concatenation. 11. Splitting strings, records and files Awk programs use the same algorithm to split strings into arrays with split(), and records into fields on FS. mawk uses essentially the same algorithm to split files into records on RS. Split(_e_x_p_r,_A,_s_e_p) works as follows: (1) If _s_e_p is omitted, it is replaced by FS. _S_e_p can be an expression or regular expression. If it is an expression of non-string type, it is converted to string. Version 1.1 Last change: Jan 22 1992 12 MAWK(1) USER COMMANDS MAWK(1) (2) If _s_e_p = " " (a single space), then <SPACE> is trimmed from the front and back of _e_x_p_r, and _s_e_p becomes <SPACE>. mawk defines <SPACE> as the reg- ular expression /[ \t\n]+/. Otherwise _s_e_p is treated as a regular expression, except that meta-characters are ignored for a string of length 1, e.g., split(x, A, "*") and split(x, A, /\*/) are the same. (3) If _e_x_p_r is not string, it is converted to string. If _e_x_p_r is then the empty string "", split() returns 0 and _A is unchanged. Otherwise, all non-overlapping, non-null and longest matches of _s_e_p in _e_x_p_r, separate _e_x_p_r into fields which are loaded into _A. The fields are placed in A[1], A[2], ..., A[n] and split() returns n, the number of fields which is the number of matches plus one. Data placed in _A that looks numeric is typed number and string. Splitting records into fields works the same except the pieces are loaded into $1, $2,..., $NF. If $0 is empty, NF is set to 0 and all $i to "". mawk splits files into records by the same algorithm, but with the slight difference that RS is really a terminator instead of a separator. (ORS is really a terminator too). E.g., if FS = ":+" and $0 = "a::b:" , then NF = 3 and $1 = "a", $2 = "b" and $3 = "", but if "a::b:" is the contents of an input file and RS = ":+", then there are two records "a" and "b". RS = " " is not special. 12. Multi-line records Since mawk interprets RS as a regular expression, multi-line records are easy. Setting RS = "\n\n+", makes one or more blank lines separate records. If FS = " " (the default), then single newlines, by the rules for <SPACE> above, become space and single newlines are field separators. For example, if a file is "a b\nc\n\n", RS = "\n\n+" and FS = " ", then there is one record "a b\nc" with three fields "a", "b" and "c". Changing FS = "\n", gives two fields "a b" and "c"; changing FS = "", gives one field identical to the record. If you want lines with spaces or tabs to be considered blank, set RS = "\n([ \t]*\n)+". For compatibility with other awks, setting RS = "" has the same effect as if blank lines are stripped from the front and back of files and then Version 1.1 Last change: Jan 22 1992 13 MAWK(1) USER COMMANDS MAWK(1) records are determined as if RS = "\n\n+". Posix requires that "\n" always separates records when RS = "" regardless of the value of FS. mawk does not support this convention, because defining "\n" as <SPACE> makes it unnecessary. Most of the time when you change RS for multi-line records, you will also want to change ORS to "\n\n" so the record spacing is preserved on output. 13. Program execution This section describes the order of program execution. First ARGC is set to the total number of command line argu- ments passed to the execution phase of the program. ARGV[0] is set the name of the AWK interpreter and ARGV[1] ... ARGV[ARGC-1] holds the remaining command line arguments exclusive of options and program source. For example with mawk -f prog v=1 A t=hello B ARGC = 5 with ARGV[0] = "mawk", ARGV[1] = "v=1", ARGV[2] = "A", ARGV[3] = "t=hello" and ARGV[4] = "B". Next, each BEGIN block is executed in order. If the program consists entirely of BEGIN blocks, then execution ter- minates, else an input stream is opened and execution con- tinues. If ARGC equals 1, the input stream is set to stdin, else the command line arguments ARGV[1] ... ARGV[ARGC-1] are examined for a file argument. The command line arguments divide into three sets: file arguments, assignment arguments and empty strings "". An assignment has the form _v_a_r=_s_t_r_i_n_g. When an ARGV[i] is examined as a possible file argument, if it is empty it is skipped; if it is an assignment argument, the assignment to _v_a_r takes place and i skips to the next argument; else ARGV[i] is opened for input. If it fails to open, execution terminates with exit code 1. If no command line argument is a file argument, then input comes from stdin. Getline in a BEGIN action opens input. "-" as a file argument denotes stdin. Once an input stream is open, each input record is tested against each _p_a_t_t_e_r_n, and if it matches, the associated _a_c_t_i_o_n is executed. An expression pattern matches if it is boolean true (see the end of section 2). A BEGIN pattern matches before any input has been read, and an END pattern matches after all input has been read. A range pattern, _e_x_p_r1,_e_x_p_r2 , matches every record between the match of _e_x_p_r1 and the match _e_x_p_r2 inclusively. When end of file occurs on the input stream, the remaining command line arguments are examined for a file argument, and Version 1.1 Last change: Jan 22 1992 14 MAWK(1) USER COMMANDS MAWK(1) if there is one it is opened, else the END _p_a_t_t_e_r_n is con- sidered matched and all END _a_c_t_i_o_n_s are executed. In the example, the assignment v=1 takes place after the BEGIN _a_c_t_i_o_n_s are executed, and the data placed in v is typed number and string. Input is then read from file A. On end of file A, t is set to the string "hello", and B is opened for input. On end of file B, the END _a_c_t_i_o_n_s are executed. Program flow at the _p_a_t_t_e_r_n {_a_c_t_i_o_n} level can be changed with the next and exit _o_p_t__e_x_p_r statements. A next statement causes the next input record to be read and pattern testing to restart with the first _p_a_t_t_e_r_n {_a_c_t_i_o_n} pair in the program. An exit statement causes immediate execution of the END actions or program termination if there are none or if the exit occurs in an END action. The _o_p_t__e_x_p_r sets the exit value of the program unless overridden by a later exit or subsequent error. EXAMPLES 1. emulate cat. { print } 2. emulate wc. { chars += length($0) + 1 # add one for the \n words += NF } END{ print NR, words, chars } 3. count the number of unique "real words". BEGIN { FS = "[^A-Za-z]+" } { for(i = 1 ; i <= NF ; i++) word[$i] = "" } END { delete word[""] for ( i in word ) cnt++ print cnt } 4. sum the second field of every record based on the first field. Version 1.1 Last change: Jan 22 1992 15 MAWK(1) USER COMMANDS MAWK(1) $1 ~ /credit|gain/ { sum += $2 } $1 ~ /debit|loss/ { sum -= $2 } END { print sum } 5. sort a file, comparing as string { line[NR] = $0 "" } # make sure of comparison type # in case some lines look numeric END { isort(line, NR) for(i = 1 ; i <= NR ; i++) print line[i] } #insertion sort of A[1..n] function isort( A, n, i, j, hold) { for( i = 2 ; i <= n ; i++) { hold = A[j = i] while ( A[j-1] > hold ) { j-- ; A[j+1] = A[j] } A[j] = hold } # sentinel A[0] = "" will be created if needed } COMPATIBILITY ISSUES The Posix 1003.2(draft 11.2) definition of the AWK language is AWK as described in the AWK book with a few extensions that appeared in SystemVR4 nawk. The extensions are: New functions: toupper() and tolower(). New variables: ENVIRON[] and CONVFMT. ANSI C conversion specifications for printf() and sprintf(). New command options: -v var=value, multiple -f options and implementation options as arguments to -W. Posix AWK is oriented to operate on files a line at a time. RS can be changed from "\n" to another single character, but it is hard to find any use for this - there are no examples in the AWK book. By convention, RS = "", makes one or more blank lines separate records, allowing multi-line records. When RS = "", "\n" is always a field separator regardless of the value in FS. Version 1.1 Last change: Jan 22 1992 16 MAWK(1) USER COMMANDS MAWK(1) mawk, on the other hand, allows RS to be a regular expres- sion. When "\n" appears in records, it is treated as space, and FS always determines fields. Removing the line at a time paradigm can make some programs simpler and can often improve performance. For example, redoing example 3 from above, BEGIN { RS = "[^A-Za-z]+" } { word[ $0 ] = "" } END { delete word[ "" ] for( i in word ) cnt++ print cnt } counts the number of unique words by making each word a record. On moderate size files, mawk executes twice as fast, because of the simplified inner loop. The following program replaces each comment by a single space in a C program file, BEGIN { RS = "/\*([^*]|\*+[^/*])*\*+/" # comment is record separator ORS = " " getline hold } { print hold ; hold = $0 } END { printf "%s" , hold } Buffering one record is needed to avoid terminating the last record with a space. With mawk, the following are all equivalent, x ~ /a\+b/ x ~ "a\+b" x ~ "a\\+b" The strings get scanned twice, once as string and once as regular expression. On the string scan, mawk ignores the escape on non-escape characters while the AWK book advocates _\_c be recognized as _c which necessitates the double escaping of meta-characters in strings. Posix explicitly declines to define the behavior which passively forces programs that must run under a variety of awks to use the more portable but less readable, double escape. Version 1.1 Last change: Jan 22 1992 17 MAWK(1) USER COMMANDS MAWK(1) Posix AWK does not recognize "/dev/stderr" or \x hex escape sequences in strings. Unlike ANSI C, mawk limits the number of digits that follows \x to two. Finally, here is how mawk handles exceptional cases not dis- cussed in the AWK book or the Posix draft. It is unsafe to assume consistency across awks and safe to skip to the next section. substr(s, i, n) returns the characters of s in the intersection of the closed interval [1, length(s)] and the half-open interval [i, i+n). When this intersec- tion is empty, the empty string is returned; so substr("ABC", 1, 0) = "" and substr("ABC", -4, 6) = "A". Every string, including the empty string, matches the empty string at the front so, s ~ // and s ~ "", are always 1 as is match(s, //) and match(s, ""). The last two set RLENGTH to 0. index(s, t) is always the same as match(s, t1) where t1 is the same as t with metacharacters escaped. Hence consistency with match requires that index(s, "") always returns 1. Also the condition, index(s,t) != 0 if and only t is a substring of s, requires index("","") = 1. If getline encounters end of file, getline var, leaves var unchanged. Similarly, on entry to the END actions, $0, the fields and NF have their value unaltered from the last record. SEE ALSO _e_g_r_e_p (1) Aho, Kernighan and Weinberger, _T_h_e _A_W_K _P_r_o_g_r_a_m_m_i_n_g _L_a_n_g_u_a_g_e, Addison-Wesley Publishing, 1988, (the AWK book), defines the language, opening with a tutorial and advancing to many interesting programs that delve into issues of software design and analysis relevant to programming in any language. _T_h_e _G_A_W_K _M_a_n_u_a_l, The Free Software Foundation, 1991, is a tutorial and language reference that does not attempt the depth of the AWK book and assumes the reader may be a novice programmer. The section on AWK arrays is excellent. It also discusses Posix requirements for AWK. Version 1.1 Last change: Jan 22 1992 18 MAWK(1) USER COMMANDS MAWK(1) BUGS mawk cannot handle ascii NUL \0 in the source or data files. You can output NUL using printf with %c, and any other 8 bit character is acceptable input. mawk implements printf() and sprintf() using the C library functions, printf and sprintf, so full ANSI compatibility requires an ANSI C library. In practice this means the h conversion qualifier may not be available. Also mawk inher- its any bugs or limitations of the library functions. Implementors of the AWK language have shown a consistent lack of imagination when naming their programs. AUTHOR Mike Brennan (brennan@boeing.com). Version 1.1 Last change: Jan 22 1992 19