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GAWK(1) Utility Commands GAWK(1) NAME gawk - pattern scanning and processing language SYNOPSIS gawk [ POSIX or GNU style options ] -f _p_r_o_g_r_a_m-_f_i_l_e [ -- ] file ... gawk [ POSIX or GNU style options ] [ -- ] _p_r_o_g_r_a_m-_t_e_x_t file ... DESCRIPTION _G_a_w_k is the GNU Project's implementation of the AWK program- ming language. It conforms to the definition of the language in the POSIX 1003.2 Command Language And Utilities Standard. This version in turn is based on the description in _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, by Aho, Kernighan, and Weinberger, with the additional features defined in the Sys- tem V Release 4 version of UNIX _a_w_k. _G_a_w_k also provides some GNU-specific extensions. The command line consists of options to _g_a_w_k itself, the AWK program text (if not supplied via the -f or --file options), and values to be made available in the ARGC and ARGV pre- defined AWK variables. OPTIONS _G_a_w_k options may be either the traditional POSIX one letter options, or the GNU style long options. POSIX style options start with a single ``-'', while GNU long options start with ``--''. GNU style long options are provided for both GNU- specific features and for POSIX mandated features. Other implementations of the AWK language are likely to only accept the traditional one letter options. Following the POSIX standard, _g_a_w_k-specific options are sup- plied via arguments to the -W option. Multiple -W options may be supplied, or multiple arguments may be supplied together if they are separated by commas, or enclosed in quotes and separated by white space. Case is ignored in arguments to the -W option. Each -W option has a corresponding GNU style long option, as detailed below. _G_a_w_k accepts the following options. -F _f_s --field-separator=_f_s Use _f_s for the input field separator (the value of the FS predefined variable). -v _v_a_r=_v_a_l --assign=_v_a_r=_v_a_l Assign the value _v_a_l, to the variable _v_a_r, before exe- cution of the program begins. Such variable values are Free Software FoundationLast change: Apr 15 1993 1 GAWK(1) Utility Commands GAWK(1) available to the BEGIN block of an AWK program. -f _p_r_o_g_r_a_m-_f_i_l_e --file=_p_r_o_g_r_a_m-_f_i_l_e Read the AWK program source from the file _p_r_o_g_r_a_m-_f_i_l_e, instead of from the first command line argument. Mul- tiple -f (or --file) options may be used. -W compat --compat Run in _c_o_m_p_a_t_i_b_i_l_i_t_y mode. In compatibility mode, _g_a_w_k behaves identically to UNIX _a_w_k; none of the GNU-specific extensions are recognized. See GNU EXTENSIONS, below, for more information. -W copyleft -W copyright --copyleft --copyright Print the short version of the GNU copyright information message on the error output. -W help -W usage --help --usage Print a relatively short summary of the avail- able options on the error output. -W lint --lint Provide warnings about constructs that are dubi- ous or non-portable to other AWK implementa- tions. -W posix --posix This turns on _c_o_m_p_a_t_i_b_i_l_i_t_y mode, with the fol- lowing additional restrictions: o+ \x escape sequences are not recognized. o+ The synonym func for the keyword function is not recognized. o+ The operators ** and **= cannot be used in place of ^ and ^=. -W source=_p_r_o_g_r_a_m-_t_e_x_t --source=_p_r_o_g_r_a_m-_t_e_x_t Use _p_r_o_g_r_a_m-_t_e_x_t as AWK program source code. This option allows the easy intermixing of library functions (used via the -f and --file options) with source code entered on the command line. It is intended primarily for medium to large size AWK programs used in shell scripts. The -W source= form of this option uses the rest of the command line argument for _p_r_o_g_r_a_m-_t_e_x_t; Free Software FoundationLast change: Apr 15 1993 2 GAWK(1) Utility Commands GAWK(1) no other options to -W will be recognized in the same argument. -W version --version Print version information for this particular copy of _g_a_w_k on the error output. This is use- ful mainly for knowing if the current copy of _g_a_w_k on your system is up to date with respect to whatever the Free Software Foundation is dis- tributing. -- Signal the end of options. This is useful to allow further arguments to the AWK program itself to start with a ``-''. This is mainly for consistency with the argument parsing con- vention used by most other POSIX programs. Any other options are flagged as illegal, but are otherwise ignored. AWK PROGRAM EXECUTION An AWK program consists of a sequence of pattern-action statements and optional function definitions. _p_a_t_t_e_r_n { _a_c_t_i_o_n _s_t_a_t_e_m_e_n_t_s } function _n_a_m_e(_p_a_r_a_m_e_t_e_r _l_i_s_t) { _s_t_a_t_e_m_e_n_t_s } _G_a_w_k first reads the program source from the _p_r_o_g_r_a_m-_f_i_l_e(s) if specified, or from the first non-option argument on the command line. The -f option may be used multiple times on the command line. _G_a_w_k will read the program text as if all the _p_r_o_g_r_a_m-_f_i_l_es had been concatenated together. This is useful for building libraries of AWK functions, without hav- ing to include them in each new AWK program that uses them. To use a library function in a file from a program typed in on the command line, specify /dev/tty as one of the _p_r_o_g_r_a_m-_f_i_l_es, type your program, and end it with a ^D (control-d). The environment variable AWKPATH specifies a search path to use when finding source files named with the -f option. If this variable does not exist, the default path is ".:/usr/lib/awk:/usr/local/lib/awk". If a file name given to the -f option contains a ``/'' character, no path search is performed. _G_a_w_k executes AWK programs in the following order. First, _g_a_w_k compiles the program into an internal form. Next, all variable assignments specified via the -v option are per- formed. Then, _g_a_w_k executes the code in the BEGIN block(s) (if any), and then proceeds to read each file named in the ARGV array. If there are no files named on the command Free Software FoundationLast change: Apr 15 1993 3 GAWK(1) Utility Commands GAWK(1) line, _g_a_w_k reads the standard input. If a filename on the command line has the form _v_a_r=_v_a_l it is treated as a variable assignment. The variable _v_a_r will be assigned the value _v_a_l. (This happens after any BEGIN block(s) have been run.) Command line variable assignment is most useful for dynamically assigning values to the vari- ables AWK uses to control how input is broken into fields and records. It is also useful for controlling state if mul- tiple passes are needed over a single data file. If the value of a particular element of ARGV is empty (""), _g_a_w_k skips over it. For each line in the input, _g_a_w_k tests to see if it matches any _p_a_t_t_e_r_n in the AWK program. For each pattern that the line matches, the associated _a_c_t_i_o_n is executed. The pat- terns are tested in the order they occur in the program. Finally, after all the input is exhausted, _g_a_w_k executes the code in the END block(s) (if any). VARIABLES AND FIELDS AWK variables are dynamic; they come into existence when they are first used. Their values are either floating-point numbers or strings, or both, depending upon how they are used. AWK also has one dimension arrays; multiply dimen- sioned arrays may be simulated. Several pre-defined vari- ables are set as a program runs; these will be described as needed and summarized below. Fields As each input line is read, _g_a_w_k splits the line into _f_i_e_l_d_s, using the value of the FS variable as the field separator. If FS is a single character, fields are separated by that character. Otherwise, FS is expected to be a full regular expression. In the special case that FS is a single blank, fields are separated by runs of blanks and/or tabs. Note that the value of IGNORECASE (see below) will also affect how fields are split when FS is a regular expression. If the FIELDWIDTHS variable is set to a space separated list of numbers, each field is expected to have fixed width, and _g_a_w_k will split up the record using the specified widths. The value of FS is ignored. Assigning a new value to FS overrides the use of FIELDWIDTHS, and restores the default behavior. Each field in the input line may be referenced by its posi- tion, $1, $2, and so on. $0 is the whole line. The value of a field may be assigned to as well. Fields need not be Free Software FoundationLast change: Apr 15 1993 4 GAWK(1) Utility Commands GAWK(1) referenced by constants: n = 5 print $n prints the fifth field in the input line. The variable NF is set to the total number of fields in the input line. References to non-existent fields (i.e. fields after $NF) produce the null-string. However, assigning to a non- existent field (e.g., $(NF+2) = 5) will increase the value of NF, create any intervening fields with the null string as their value, and cause the value of $0 to be recomputed, with the fields being separated by the value of OFS. Built-in Variables AWK's built-in variables are: ARGC The number of command line arguments (does not include options to _g_a_w_k, or the program source). ARGIND The index in ARGV of the current file being pro- cessed. ARGV Array of command line arguments. The array is indexed from 0 to ARGC - 1. Dynamically chang- ing the contents of ARGV can control the files used for data. CONVFMT The conversion format for numbers, "%.6g", by default. ENVIRON An array containing the values of the current environment. The array is indexed by the environment variables, each element being the value of that variable (e.g., ENVIRON["HOME"] might be /u/arnold). Changing this array does not affect the environment seen by programs which _g_a_w_k spawns via redirection or the sys- tem() function. (This may change in a future version of _g_a_w_k.) ERRNO If a system error occurs either doing a redirec- tion for getline, during a read for getline, or during a close, then ERRNO will contain a string describing the error. FIELDWIDTHS A white-space separated list of fieldwidths. When set, _g_a_w_k parses the input into fields of fixed width, instead of using the value of the FS variable as the field separator. The fixed field width facility is still experimental; Free Software FoundationLast change: Apr 15 1993 5 GAWK(1) Utility Commands GAWK(1) expect the semantics to change as _g_a_w_k evolves over time. FILENAME The name of the current input file. If no files are specified on the command line, the value of FILENAME is ``-''. FNR The input record number in the current input file. FS The input field separator, a blank by default. IGNORECASE Controls the case-sensitivity of all regular expression operations. If IGNORECASE has a non- zero value, then pattern matching in rules, field splitting with FS, regular expression matching with ~ and !~, and the gsub(), index(), match(), split(), and sub() pre-defined func- tions will all ignore case when doing regular expression operations. Thus, if IGNORECASE is not equal to zero, /aB/ matches all of the strings "ab", "aB", "Ab", and "AB". As with all AWK variables, the initial value of IGNORECASE is zero, so all regular expression operations are normally case-sensitive. NF The number of fields in the current input record. NR The total number of input records seen so far. OFMT The output format for numbers, "%.6g", by default. OFS The output field separator, a blank by default. ORS The output record separator, by default a new- line. RS The input record separator, by default a new- line. RS is exceptional in that only the first character of its string value is used for separating records. (This will probably change in a future release of _g_a_w_k.) If RS is set to the null string, then records are separated by blank lines. When RS is set to the null string, then the newline character always acts as a field separator, in addition to whatever value FS may have. RSTART The index of the first character matched by match(); 0 if no match. Free Software FoundationLast change: Apr 15 1993 6 GAWK(1) Utility Commands GAWK(1) RLENGTH The length of the string matched by match(); -1 if no match. SUBSEP The character used to separate multiple sub- scripts in array elements, by default "\034". Arrays Arrays are subscripted with an expression between square brackets ([ and ]). If the expression is an expression list (_e_x_p_r, _e_x_p_r ...) then the array subscript is a string con- sisting of the concatenation of the (string) value of each expression, separated by the value of the SUBSEP variable. This facility is used to simulate multiply dimensioned arrays. For example: i = "A" ; j = "B" ; k = "C" x[i, j, k] = "hello, world\n" assigns the string "hello, world\n" to the element of the array x which is indexed by the string "A\034B\034C". All arrays in AWK are associative, i.e. indexed by string values. The special operator in may be used in an if or while state- ment to see if an array has an index consisting of a partic- ular value. if (val in array) print array[val] If the array has multiple subscripts, use (i, j) in array. The in construct may also be used in a for loop to iterate over all the elements of an array. An element may be deleted from an array using the delete statement. Variable Typing And Conversion Variables and fields may be (floating point) numbers, or strings, or both. How the value of a variable is interpreted depends upon its context. If used in a numeric expression, it will be treated as a number, if used as a string it will be treated as a string. To force a variable to be treated as a number, add 0 to it; to force it to be treated as a string, concatenate it with the null string. When a string must be converted to a number, the conversion is accomplished using _a_t_o_f(3). A number is converted to a string by using the value of CONVFMT as a format string for Free Software FoundationLast change: Apr 15 1993 7 GAWK(1) Utility Commands GAWK(1) _s_p_r_i_n_t_f(3), with the numeric value of the variable as the argument. However, even though all numbers in AWK are floating-point, integral values are _a_l_w_a_y_s converted as integers. Thus, given CONVFMT = "%2.2f" a = 12 b = a "" the variable b has a value of "12" and not "12.00". _G_a_w_k performs comparisons as follows: If two variables are numeric, they are compared numerically. If one value is numeric and the other has a string value that is a ``numeric string,'' then comparisons are also done numerically. Oth- erwise, the numeric value is converted to a string and a string comparison is performed. Two strings are compared, of course, as strings. According to the POSIX standard, even if two strings are numeric strings, a numeric com- parison is performed. However, this is clearly incorrect, and _g_a_w_k does not do this. Uninitialized variables have the numeric value 0 and the string value "" (the null, or empty, string). PATTERNS AND ACTIONS AWK is a line oriented language. The pattern comes first, and then the action. Action statements are enclosed in { and }. Either the pattern may be missing, or the action may be missing, but, of course, not both. If the pattern is miss- ing, the action will be executed for every single line of input. A missing action is equivalent to { print } which prints the entire line. Comments begin with the ``#'' character, and continue until the end of the line. Blank lines may be used to separate statements. Normally, a statement ends with a newline, how- ever, this is not the case for lines ending in a ``,'', ``{'', ``?'', ``:'', ``&&'', or ``||''. Lines ending in do or else also have their statements automatically continued on the following line. In other cases, a line can be con- tinued by ending it with a ``\'', in which case the newline will be ignored. Multiple statements may be put on one line by separating them with a ``;''. This applies to both the statements within the action part of a pattern-action pair (the usual case), and to the pattern-action statements themselves. Free Software FoundationLast change: Apr 15 1993 8 GAWK(1) Utility Commands GAWK(1) Patterns AWK patterns may be one of the following: BEGIN END /_r_e_g_u_l_a_r _e_x_p_r_e_s_s_i_o_n/ _r_e_l_a_t_i_o_n_a_l _e_x_p_r_e_s_s_i_o_n _p_a_t_t_e_r_n && _p_a_t_t_e_r_n _p_a_t_t_e_r_n || _p_a_t_t_e_r_n _p_a_t_t_e_r_n ? _p_a_t_t_e_r_n : _p_a_t_t_e_r_n (_p_a_t_t_e_r_n) ! _p_a_t_t_e_r_n _p_a_t_t_e_r_n_1, _p_a_t_t_e_r_n_2 BEGIN and END are two special kinds of patterns which are not tested against the input. The action parts of all BEGIN patterns are merged as if all the statements had been writ- ten in a single BEGIN block. They are executed before any of the input is read. Similarly, all the END blocks are merged, and executed when all the input is exhausted (or when an exit statement is executed). BEGIN and END patterns cannot be combined with other patterns in pattern expressions. BEGIN and END patterns cannot have missing action parts. For /_r_e_g_u_l_a_r _e_x_p_r_e_s_s_i_o_n/ patterns, the associated statement is executed for each input line that matches the regular expression. Regular expressions are the same as those in _e_g_r_e_p(1), and are summarized below. A _r_e_l_a_t_i_o_n_a_l _e_x_p_r_e_s_s_i_o_n may use any of the operators defined below in the section on actions. These generally test whether certain fields match certain regular expressions. The &&, ||, and ! operators are logical AND, logical OR, and logical NOT, respectively, as in C. They do short-circuit evaluation, also as in C, and are used for combining more primitive pattern expressions. As in most languages, parentheses may be used to change the order of evaluation. The ?: operator is like the same operator in C. If the first pattern is true then the pattern used for testing is the second pattern, otherwise it is the third. Only one of the second and third patterns is evaluated. The _p_a_t_t_e_r_n_1, _p_a_t_t_e_r_n_2 form of an expression is called a range pattern. It matches all input records starting with a line that matches _p_a_t_t_e_r_n_1, and continuing until a record that matches _p_a_t_t_e_r_n_2, inclusive. It does not combine with any other sort of pattern expression. Regular Expressions Regular expressions are the extended kind found in _e_g_r_e_p. Free Software FoundationLast change: Apr 15 1993 9 GAWK(1) Utility Commands GAWK(1) They are composed of characters as follows: _c matches the non-metacharacter _c. _\_c matches the literal character _c. . matches any character except newline. ^ matches the beginning of a line or a string. $ matches the end of a line or a string. [_a_b_c...] character class, matches any of the characters _a_b_c.... [^_a_b_c...] negated character class, matches any character except _a_b_c... and newline. _r_1|_r_2 alternation: matches either _r_1 or _r_2. _r_1_r_2 concatenation: matches _r_1, and then _r_2. _r+ matches one or more _r's. _r* matches zero or more _r's. _r? matches zero or one _r's. (_r) grouping: matches _r. The escape sequences that are valid in string constants (see below) are also legal in regular expressions. Actions Action statements are enclosed in braces, { and }. Action statements consist of the usual assignment, conditional, and looping statements found in most languages. The operators, control statements, and input/output statements available are patterned after those in C. Operators The operators in AWK, in order of increasing precedence, are = += -= *= /= %= ^= Assignment. Both absolute assignment (_v_a_r = _v_a_l_u_e) and operator-assignment (the other forms) are supported. ?: The C conditional expression. This has the form _e_x_p_r_1 ? _e_x_p_r_2 : _e_x_p_r_3. If _e_x_p_r_1 is true, the value of the expression is _e_x_p_r_2, otherwise it is _e_x_p_r_3. Only one of _e_x_p_r_2 and _e_x_p_r_3 is Free Software FoundationLast change: Apr 15 1993 10 GAWK(1) Utility Commands GAWK(1) evaluated. || Logical OR. && Logical AND. ~ !~ Regular expression match, negated match. NOTE: Do not use a constant regular expression (/foo/) on the left-hand side of a ~ or !~. Only use one on the right-hand side. The expression /foo/ ~ _e_x_p has the same meaning as (($0 ~ /foo/) ~ _e_x_p). This is usually _n_o_t what was intended. < > <= >= != == The regular relational operators. _b_l_a_n_k String concatenation. + - Addition and subtraction. * / % Multiplication, division, and modulus. + - ! Unary plus, unary minus, and logical negation. ^ Exponentiation (** may also be used, and **= for the assignment operator). ++ -- Increment and decrement, both prefix and post- fix. $ Field reference. Control Statements The control statements are as follows: if (_c_o_n_d_i_t_i_o_n) _s_t_a_t_e_m_e_n_t [ else _s_t_a_t_e_m_e_n_t ] while (_c_o_n_d_i_t_i_o_n) _s_t_a_t_e_m_e_n_t do _s_t_a_t_e_m_e_n_t while (_c_o_n_d_i_t_i_o_n) for (_e_x_p_r_1; _e_x_p_r_2; _e_x_p_r_3) _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 break continue delete _a_r_r_a_y[_i_n_d_e_x] exit [ _e_x_p_r_e_s_s_i_o_n ] { _s_t_a_t_e_m_e_n_t_s } I/O Statements The input/output statements are as follows: Free Software FoundationLast change: Apr 15 1993 11 GAWK(1) Utility Commands GAWK(1) close(_f_i_l_e_n_a_m_e) Close file (or pipe, see below). getline Set $0 from next input record; set NF, NR, FNR. getline <_f_i_l_e Set $0 from next record of _f_i_l_e; set NF. getline _v_a_r Set _v_a_r from next input record; set NF, FNR. getline _v_a_r <_f_i_l_e Set _v_a_r from next record of _f_i_l_e. next Stop processing the current input record. The next input record is read and processing starts over with the first pattern in the AWK program. If the end of the input data is reached, the END block(s), if any, are exe- cuted. next file Stop processing the current input file. The next input record read comes from the next input file. FILENAME is updated, FNR is reset to 1, and processing starts over with the first pattern in the AWK program. If the end of the input data is reached, the END block(s), if any, are exe- cuted. print Prints the current record. print _e_x_p_r-_l_i_s_t Prints expressions. print _e_x_p_r-_l_i_s_t >_f_i_l_e Prints expressions on _f_i_l_e. printf _f_m_t, _e_x_p_r-_l_i_s_t Format and print. printf _f_m_t, _e_x_p_r-_l_i_s_t >_f_i_l_e Format and print on _f_i_l_e. system(_c_m_d-_l_i_n_e) Execute the command _c_m_d-_l_i_n_e, and return the exit status. (This may not be available on non-POSIX systems.) Other input/output redirections are also allowed. For print and printf, >>_f_i_l_e appends output to the _f_i_l_e, while | _c_o_m_- _m_a_n_d writes on a pipe. In a similar fashion, _c_o_m_m_a_n_d | get- line pipes into getline. Getline will return 0 on end of file, and -1 on an error. Free Software FoundationLast change: Apr 15 1993 12 GAWK(1) Utility Commands GAWK(1) The _p_r_i_n_t_f Statement The AWK versions of the printf statement and sprintf() func- tion (see below) accept the following conversion specifica- tion formats: %c An ASCII character. If the argument used for %c is numeric, it is treated as a character and printed. Otherwise, the argument is assumed to be a string, and the only first character of that string is printed. %d A decimal number (the integer part). %i Just like %d. %e A floating point number of the form [-]d.ddddddE[+-]dd. %f A floating point number of the form [-]ddd.dddddd. %g Use e or f conversion, whichever is shorter, with non- significant zeros suppressed. %o An unsigned octal number (again, an integer). %s A character string. %x An unsigned hexadecimal number (an integer). %X Like %x, but using ABCDEF instead of abcdef. %% A single % character; no argument is converted. There are optional, additional parameters that may lie between the % and the control letter: - The expression should be left-justified within its field. _w_i_d_t_h The field should be padded to this width. If the number has a leading zero, then the field will be padded with zeros. Otherwise it is padded with blanks. ._p_r_e_c A number indicating the maximum width of strings or digits to the right of the decimal point. The dynamic _w_i_d_t_h and _p_r_e_c capabilities of the ANSI C printf() routines are supported. A * in place of either the width or prec specifications will cause their values to be taken from the argument list to printf or sprintf(). Free Software FoundationLast change: Apr 15 1993 13 GAWK(1) Utility Commands GAWK(1) Special File Names When doing I/O redirection from either print or printf into a file, or via getline from a file, _g_a_w_k recognizes certain special filenames internally. These filenames allow access to open file descriptors inherited from _g_a_w_k's parent pro- cess (usually the shell). Other special filenames provide access information about the running gawk process. The filenames are: /dev/pid Reading this file returns the process ID of the current process, in decimal, terminated with a newline. /dev/ppid Reading this file returns the parent process ID of the current process, in decimal, terminated with a newline. /dev/pgrpid Reading this file returns the process group ID of the current process, in decimal, terminated with a newline. /dev/user Reading this file returns a single record ter- minated with a newline. The fields are separated with blanks. $1 is the value of the _g_e_t_u_i_d(2) system call, $2 is the value of the _g_e_t_e_u_i_d(2) system call, $3 is the value of the _g_e_t_g_i_d(2) system call, and $4 is the value of the _g_e_t_e_g_i_d(2) system call. If there are any additional fields, they are the group IDs returned by _g_e_t_g_r_o_u_p_s(2). (Multiple groups may not be supported on all systems.) /dev/stdin The standard input. /dev/stdout The standard output. /dev/stderr The standard error output. /dev/fd/_n The file associated with the open file descrip- tor _n. These are particularly useful for error messages. For exam- ple: print "You blew it!" > "/dev/stderr" whereas you would otherwise have to use print "You blew it!" | "cat 1>&2" These file names may also be used on the command line to name data files. Free Software FoundationLast change: Apr 15 1993 14 GAWK(1) Utility Commands GAWK(1) Numeric Functions AWK has the following pre-defined arithmetic functions: atan2(_y, _x) returns the arctangent of _y/_x in radians. cos(_e_x_p_r) returns the cosine in radians. exp(_e_x_p_r) the exponential function. int(_e_x_p_r) truncates to integer. log(_e_x_p_r) the natural logarithm function. rand() returns a random number between 0 and 1. sin(_e_x_p_r) returns the sine in radians. sqrt(_e_x_p_r) the square root function. srand(_e_x_p_r) use _e_x_p_r as a new seed for the random number generator. If no _e_x_p_r is provided, the time of day will be used. The return value is the pre- vious seed for the random number generator. String Functions AWK has the following pre-defined string functions: gsub(_r, _s, _t) for each substring matching the reg- ular expression _r in the string _t, substitute the string _s, and return the number of substitutions. If _t is not supplied, use $0. index(_s, _t) returns the index of the string _t in the string _s, or 0 if _t is not present. length(_s) returns the length of the string _s, or the length of $0 if _s is not sup- plied. match(_s, _r) returns the position in _s where the regular expression _r occurs, or 0 if _r is not present, and sets the values of RSTART and RLENGTH. split(_s, _a, _r) splits the string _s into the array _a on the regular expression _r, and returns the number of fields. If _r is omitted, FS is used instead. sprintf(_f_m_t, _e_x_p_r-_l_i_s_t) prints _e_x_p_r-_l_i_s_t according to _f_m_t, Free Software FoundationLast change: Apr 15 1993 15 GAWK(1) Utility Commands GAWK(1) and returns the resulting string. sub(_r, _s, _t) just like gsub(), but only the first matching substring is replaced. substr(_s, _i, _n) returns the _n-character substring of _s starting at _i. If _n is omitted, the rest of _s is used. tolower(_s_t_r) returns a copy of the string _s_t_r, with all the upper-case characters in _s_t_r translated to their corresponding lower-case counter- parts. Non-alphabetic characters are left unchanged. toupper(_s_t_r) returns a copy of the string _s_t_r, with all the lower-case characters in _s_t_r translated to their corresponding upper-case counter- parts. Non-alphabetic characters are left unchanged. Time Functions Since one of the primary uses of AWK programs is processing log files that contain time stamp information, _g_a_w_k provides the following two functions for obtaining time stamps and formatting them. systime() returns the current time of day as the number of seconds since the Epoch (Midnight UTC, January 1, 1970 on POSIX systems). strftime(_f_o_r_m_a_t, _t_i_m_e_s_t_a_m_p) formats _t_i_m_e_s_t_a_m_p according to the specification in _f_o_r_m_a_t. The _t_i_m_e_s_t_a_m_p should be of the same form as returned by systime(). If _t_i_m_e_s_t_a_m_p is missing, the current time of day is used. See the specification for the strftime() function in ANSI C for the format conversions that are guaranteed to be available. A public-domain version of _s_t_r_f_t_i_m_e(3) and a man page for it are shipped with _g_a_w_k; if that version was used to build _g_a_w_k, then all of the conversions described in that man page are available to _g_a_w_k. String Constants String constants in AWK are sequences of characters enclosed between double quotes ("). Within strings, certain _e_s_c_a_p_e _s_e_q_u_e_n_c_e_s are recognized, as in C. These are: Free Software FoundationLast change: Apr 15 1993 16 GAWK(1) Utility Commands GAWK(1) \\ A literal backslash. \a The ``alert'' character; usually the ASCII BEL charac- ter. \b backspace. \f form-feed. \n new line. \r carriage return. \t horizontal tab. \v vertical tab. \x_h_e_x _d_i_g_i_t_s The character represented by the string of hexadecimal digits following the \x. As in ANSI C, all following hexadecimal digits are considered part of the escape sequence. (This feature should tell us something about language design by committee.) E.g., "\x1B" is the ASCII ESC (escape) character. \_d_d_d The character represented by the 1-, 2-, or 3-digit sequence of octal digits. E.g. "\033" is the ASCII ESC (escape) character. \_c The literal character _c. The escape sequences may also be used inside constant regu- lar expressions (e.g., /[ \t\f\n\r\v]/ matches whitespace characters). FUNCTIONS Functions in AWK are defined as follows: function _n_a_m_e(_p_a_r_a_m_e_t_e_r _l_i_s_t) { _s_t_a_t_e_m_e_n_t_s } Functions are executed when called from within the action parts of regular pattern-action statements. Actual parame- ters supplied in the function call are used to instantiate the formal parameters declared in the function. Arrays are passed by reference, other variables are passed by value. Since functions were not originally part of the AWK language, the provision for local variables is rather clumsy: They are declared as extra parameters in the parame- ter list. The convention is to separate local variables from real parameters by extra spaces in the parameter list. For example: Free Software FoundationLast change: Apr 15 1993 17 GAWK(1) Utility Commands GAWK(1) function f(p, q, a, b) { # a & b are local ..... } /abc/ { ... ; f(1, 2) ; ... } The left parenthesis in a function call is required to immediately follow the function name, without any interven- ing white space. This is to avoid a syntactic ambiguity with the concatenation operator. This restriction does not apply to the built-in functions listed above. Functions may call each other and may be recursive. Func- tion parameters used as local variables are initialized to the null string and the number zero upon function invoca- tion. The word func may be used in place of function. EXAMPLES Print and sort the login names of all users: BEGIN { FS = ":" } { print $1 | "sort" } Count lines in a file: { nlines++ } END { print nlines } Precede each line by its number in the file: { print FNR, $0 } Concatenate and line number (a variation on a theme): { print NR, $0 } SEE ALSO _e_g_r_e_p(1) _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, Alfred V. Aho, Brian W. Ker- nighan, Peter J. Weinberger, Addison-Wesley, 1988. ISBN 0- 201-07981-X. _T_h_e _G_A_W_K _M_a_n_u_a_l, Edition 0.15, published by the Free Software Foundation, 1993. POSIX COMPATIBILITY A primary goal for _g_a_w_k is compatibility with the POSIX standard, as well as with the latest version of UNIX _a_w_k. To this end, _g_a_w_k incorporates the following user visible features which are not described in the AWK book, but are Free Software FoundationLast change: Apr 15 1993 18 GAWK(1) Utility Commands GAWK(1) part of _a_w_k in System V Release 4, and are in the POSIX standard. The -v option for assigning variables before program execu- tion starts is new. The book indicates that command line variable assignment happens when _a_w_k would otherwise open the argument as a file, which is after the BEGIN block is executed. However, in earlier implementations, when such an assignment appeared before any file names, the assignment would happen _b_e_f_o_r_e the BEGIN block was run. Applications came to depend on this ``feature.'' When _a_w_k was changed to match its documentation, this option was added to accomodate applications that depended upon the old behavior. (This feature was agreed upon by both the AT&T and GNU develop- ers.) The -W option for implementation specific features is from the POSIX standard. When processing arguments, _g_a_w_k uses the special option ``--'' to signal the end of arguments, and warns about, but otherwise ignores, undefined options. The AWK book does not define the return value of srand(). The System V Release 4 version of UNIX _a_w_k (and the POSIX standard) has it return the seed it was using, to allow keeping track of random number sequences. Therefore srand() in _g_a_w_k also returns its current seed. Other new features are: The use of multiple -f options (from MKS _a_w_k); the ENVIRON array; the \a, and \v escape sequences (done originally in _g_a_w_k and fed back into AT&T's); the tolower() and toupper() built-in functions (from AT&T); and the ANSI C conversion specifications in printf (done first in AT&T's version). GNU EXTENSIONS _G_a_w_k has some extensions to POSIX _a_w_k. They are described in this section. All the extensions described here can be disabled by invoking _g_a_w_k with the -W compat option. The following features of _g_a_w_k are not available in POSIX _a_w_k. o+ The \x escape sequence. o+ The systime() and strftime() functions. o+ The special file names available for I/O redirection are not recognized. o+ The ARGIND and ERRNO variables are not special. Free Software FoundationLast change: Apr 15 1993 19 GAWK(1) Utility Commands GAWK(1) o+ The IGNORECASE variable and its side-effects are not available. o+ The FIELDWIDTHS variable and fixed width field split- ting. o+ No path search is performed for files named via the -f option. Therefore the AWKPATH environment vari- able is not special. o+ The use of next file to abandon processing of the current input file. The AWK book does not define the return value of the close() function. _G_a_w_k's close() returns the value from _f_c_l_o_s_e(3), or _p_c_l_o_s_e(3), when closing a file or pipe, respectively. When _g_a_w_k is invoked with the -W compat option, if the _f_s argument to the -F option is ``t'', then FS will be set to the tab character. Since this is a rather ugly special case, it is not the default behavior. This behavior also does not occur if -Wposix has been specified. HISTORICAL FEATURES There are two features of historical AWK implementations that _g_a_w_k supports. First, it is possible to call the length() built-in function not only with no argument, but even without parentheses! Thus, a = length is the same as either of a = length() a = length($0) This feature is marked as ``deprecated'' in the POSIX stan- dard, and _g_a_w_k will issue a warning about its use if -Wlint is specified on the command line. The other feature is the use of the continue statement out- side the body of a while, for, or do loop. Traditional AWK implementations have treated such usage as equivalent to the next statement. _G_a_w_k will support this usage if -Wposix has not been specified. BUGS The -F option is not necessary given the command line vari- able assignment feature; it remains only for backwards com- patibility. Free Software FoundationLast change: Apr 15 1993 20 GAWK(1) Utility Commands GAWK(1) If your system actually has support for /dev/fd and the associated /dev/stdin, /dev/stdout, and /dev/stderr files, you may get different output from _g_a_w_k than you would get on a system without those files. When _g_a_w_k interprets these files internally, it synchronizes output to the standard output with output to /dev/stdout, while on a system with those files, the output is actually to different open files. Caveat Emptor. VERSION INFORMATION This man page documents _g_a_w_k, version 2.15. Starting with the 2.15 version of _g_a_w_k, the -c, -V, -C, -a, and -e options of the 2.11 version are no longer recognized. AUTHORS The original version of UNIX _a_w_k was designed and imple- mented by Alfred Aho, Peter Weinberger, and Brian Kernighan of AT&T Bell Labs. Brian Kernighan continues to maintain and enhance it. Paul Rubin and Jay Fenlason, of the Free Software Founda- tion, wrote _g_a_w_k, to be compatible with the original version of _a_w_k distributed in Seventh Edition UNIX. John Woods con- tributed a number of bug fixes. David Trueman, with contri- butions from Arnold Robbins, made _g_a_w_k compatible with the new version of UNIX _a_w_k. The initial DOS port was done by Conrad Kwok and Scott Gar- finkle. Scott Deifik is the current DOS maintainer. Pat Rankin did the port to VMS, and Michal Jaegermann did the port to the Atari ST. ACKNOWLEDGEMENTS Brian Kernighan of Bell Labs provided valuable assistance during testing and debugging. We thank him. Free Software FoundationLast change: Apr 15 1993 21