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GAWK User Commands GAWK NNAAMMEE gawk - pattern scanning and processing language SSYYNNOOPPSSIISS ggaawwkk [ --aa ] [ --ee ] [ --cc ] [ --CC ] [ --VV ] [ --FF_f_s ] [ --vv _v_a_r=_v_a_l ] --ff _p_r_o_g_r_a_m-_f_i_l_e [ ---- ] file ... ggaawwkk [ --aa ] [ --ee ] [ --cc ] [ --CC ] [ --VV ] [ --FF_f_s ] [ --vv _v_a_r=_v_a_l ] [ ---- ] _p_r_o_g_r_a_m-_t_e_x_t file ... DDEESSCCRRIIPPTTIIOONN _G_a_w_k is the GNU Project's implementation of the AWK program- ming language. It conforms to the definition and descrip- tion of the language 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 System V Release 4 version of UNIX _a_w_k, and 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 --ff option), and values to be made available in the AARRGGCC and AARRGGVV pre-defined AWK variables. _G_a_w_k accepts the following options, which should be avail- able on any implementation of the AWK language. --FF_f_s Use _f_s for the input field separator (the value of the FFSS predefined variable). --vv _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 available to the BBEEGGIINN block of an AWK program. --ff _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 --ff options may be used. ---- 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 convention used by most other System V programs. The following options are specific to the GNU implementa- tion. --aa Use AWK style regular expressions as described in the book. This is the current default, but may not be when the POSIX P1003.2 standard is finalized. It is orthog- onal to --cc. Free Software Foundation August 24 1989 1 GAWK User Commands GAWK --ee Use _e_g_r_e_p(1) style regular expressions as described in POSIX standard. This may become the default when the POSIX P1003.2 standard is finalized. It is orthogonal to --cc. --cc 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. --CC Print the short version of the GNU copyright informa- tion message on the error output. This option may disappear in a future version of _g_a_w_k. --VV Print version information for this particular copy of _g_a_w_k on the error output. This is useful 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 distributing. This option may disappear in a future version of _g_a_w_k. Any other options are flagged as illegal, but are otherwise ignored. 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 }} ffuunnccttiioonn _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 --ff 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 //ddeevv//ttttyy as one of the _p_r_o_g_r_a_m-_f_i_l_es, type your program, and end it with a ^^DD (control-d). The environment variable AAWWKKPPAATTHH specifies a search path to use when finding source files named with the --ff option. If this variable does not exist, the default path is ""..:://uussrr//lliibb//aawwkk:://uussrr//llooccaall//lliibb//aawwkk"". If a file name given to the --ff option contains a ``/'' character, no path search is performed. _G_a_w_k compiles the program into an internal form, executes the code in the BBEEGGIINN block(s) (if any), and then proceeds to read each file named in the AARRGGVV array. If there are no files named on the command line, _g_a_w_k reads the standard Free Software Foundation August 24 1989 2 GAWK User Commands GAWK input. If a ``file'' named 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 is most useful for dynamically assigning values to the variables AWK uses to control how input is broken into fields and records. It is also useful for controlling state if multiple passes are needed over a single data file. 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. VVAARRIIAABBLLEESS AANNDD FFIIEELLDDSS AWK variables are dynamic; they come into existence when they are first used. Their values are either floating-point numbers or strings, depending upon how they are used. AWK also has one dimension arrays; multiply dimensioned arrays may be simulated. There are several pre-defined variables that AWK sets as a program runs; these will be described as needed and summarized below. FFiieellddss 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 FFSS variable as the field separator. If FFSS is a single character, fields are separated by that character. Otherwise, FFSS is expected to be a full regular expression. In the special case that FFSS is a single blank, fields are separated by runs of blanks and/or tabs. Note that the value of IIGGNNOORREECCAASSEE (see below) will also affect how fields are split when FFSS is a regular expression. Each field in the input line may be referenced by its posi- tion, $$11, $$22, and so on. $$00 is the whole line. The value of a field may be assigned to as well. Fields need not be referenced by constants: nn == 55 pprriinntt $$nn prints the fifth field in the input line. The variable NNFF is set to the total number of fields in the input line. References to non-existent fields (i.e. fields after $$NNFF), produce the null-string. However, assigning to a non- existent field (e.g., $$((NNFF++22)) == 55) will increase the value of NNFF, create any intervening fields with the null string as their value, and cause the value of $$00 to be recomputed, Free Software Foundation August 24 1989 3 GAWK User Commands GAWK with the fields being separated by the value of OOFFSS. BBuuiilltt--iinn VVaarriiaabblleess AWK's built-in variables are: AARRGGCC the number of command line arguments (does not include options to _g_a_w_k, or the program source). AARRGGVV array of command line arguments. The array is indexed from 0 to AARRGGCC - 1. Dynamically changing the contents of AARRGGVV can control the files used for data. EENNVVIIRROONN An array containing the values of the current environment. The array is indexed by the environ- ment variables, each element being the value of that variable (e.g., EENNVVIIRROONN[[""HHOOMMEE""]] might be //uu//aarrnnoolldd). Changing this array does not affect the environment seen by programs which _g_a_w_k spawns via redirection or the ssyysstteemm function. (This may change in a future version of _g_a_w_k.) FFIILLEENNAAMMEE the name of the current input file. If no files are specified on the command line, the value of FFIILLEENNAAMMEE is ``-''. FFNNRR the input record number in the current input file. FFSS the input field separator, a blank by default. IIGGNNOORREECCAASSEE Controls the case-sensitivity of all regular expression operations. If IIGGNNOORREECCAASSEE has a non- zero value, then pattern matching in rules, field splitting with FFSS, regular expression matching with ~~ and !!~~, and the ggssuubb(()), iinnddeexx(()), mmaattcchh(()), sspplliitt(()), and ssuubb(()) pre-defined functions will all ignore case when doing regular expression opera- tions. Thus, if IIGGNNOORREECCAASSEE is not equal to zero, //aaBB// matches all of the strings ""aabb"", ""aaBB"", ""AAbb"", and ""AABB"". As with all AWK variables, the initial value of IIGGNNOORREECCAASSEE is zero, so all regular expression operations are normally case-sensitive. NNFF the number of fields in the current input record. NNRR the total number of input records seen so far. OOFFMMTT the output format for numbers, %%..66gg by default. Free Software Foundation August 24 1989 4 GAWK User Commands GAWK OOFFSS the output field separator, a blank by default. OORRSS the output record separator, by default a newline. RRSS the input record separator, by default a newline. RRSS is exceptional in that only the first character of its string value is used for separating records. If RRSS is set to the null string, then records are separated by blank lines. When RRSS is set to the null string, then the newline character always acts as a field separator, in addition to whatever value FFSS may have. RRSSTTAARRTT the index of the first character matched by mmaattcchh(()); 0 if no match. RRLLEENNGGTTHH the length of the string matched by mmaattcchh(()); -1 if no match. SSUUBBSSEEPP the character used to separate multiple subscripts in array elements, by default ""\\003344"". AArrrraayyss 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 SSUUBBSSEEPP variable. This facility is used to simulate multiply dimensioned arrays. For example: ii == ""AA"" ;; jj == ""BB"" ;; kk == ""CC"" xx[[ii,, jj,, kk]] == ""hheelllloo,, wwoorrlldd\\nn"" assigns the string ""hheelllloo,, wwoorrlldd\\nn"" to the element of the array xx which is indexed by the string ""AA\\003344BB\\003344CC"". All arrays in AWK are associative, i.e. indexed by string values. The special operator iinn may be used in an iiff or wwhhiillee state- ment to see if an array has an index consisting of a partic- ular value. iiff ((vvaall iinn aarrrraayy)) pprriinntt aarrrraayy[[vvaall]] If the array has multiple subscripts, use ((ii,, jj)) iinn aarrrraayy. Free Software Foundation August 24 1989 5 GAWK User Commands GAWK The iinn construct may also be used in a ffoorr loop to iterate over all the elements of an array. An element may be deleted from an array using the ddeelleettee statement. VVaarriiaabbllee TTyyppiinngg 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. The AWK language defines comparisons as being done numeri- cally if possible, otherwise one or both operands are con- verted to strings and a string comparison is performed. Uninitialized variables have the numeric value 0 and the string value "" (the null, or empty, string). PPAATTTTEERRNNSS AANNDD AACCTTIIOONNSS 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 {{ pprriinntt }} 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 ddoo or eellssee 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 Free Software Foundation August 24 1989 6 GAWK User Commands GAWK case), and to the pattern-action statements themselves. PPaatttteerrnnss AWK patterns may be one of the following: BBEEGGIINN EENNDD //_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 BBEEGGIINN and EENNDD are two special kinds of patterns which are not tested against the input. The action parts of all BBEEGGIINN patterns are merged as if all the statements had been writ- ten in a single BBEEGGIINN block. They are executed before any of the input is read. Similarly, all the EENNDD blocks are merged, and executed when all the input is exhausted (or when an eexxiitt statement is executed). BBEEGGIINN and EENNDD patterns cannot be combined with other patterns in pattern expressions. BBEEGGIINN and EENNDD 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 lines starting with a line that matches _p_a_t_t_e_r_n_1, and continuing until a line that matches _p_a_t_t_e_r_n_2, inclusive. It does not combine with any Free Software Foundation August 24 1989 7 GAWK User Commands GAWK other sort of pattern expression. RReegguullaarr EExxpprreessssiioonnss Regular expressions are the extended kind found in _e_g_r_e_p. 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. AAccttiioonnss 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. OOppeerraattoorrss The operators in AWK, in order of increasing precedence, are == ++== --== **== //== %%== ^^== Assignment. Both absolute assignment ((_v_a_r == _v_a_l_u_e)) Free Software Foundation August 24 1989 8 GAWK User Commands GAWK and operator-assignment (the other forms) are sup- ported. ??:: 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 evaluated. |||| logical OR. &&&& logical AND. ~~ !!~~ regular expression match, negated match. << <<== >> >>== !!== ==== 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 postfix. $$ field reference. CCoonnttrrooll SSttaatteemmeennttss The control statements are as follows: iiff ((_c_o_n_d_i_t_i_o_n)) _s_t_a_t_e_m_e_n_t [ eellssee _s_t_a_t_e_m_e_n_t ] wwhhiillee ((_c_o_n_d_i_t_i_o_n)) _s_t_a_t_e_m_e_n_t ddoo _s_t_a_t_e_m_e_n_t wwhhiillee ((_c_o_n_d_i_t_i_o_n)) ffoorr ((_e_x_p_r_1;; _e_x_p_r_2;; _e_x_p_r_3)) _s_t_a_t_e_m_e_n_t ffoorr ((_v_a_r iinn _a_r_r_a_y)) _s_t_a_t_e_m_e_n_t bbrreeaakk ccoonnttiinnuuee ddeelleettee _a_r_r_a_y[[_i_n_d_e_x]] eexxiitt [ _e_x_p_r_e_s_s_i_o_n ] {{ _s_t_a_t_e_m_e_n_t_s }} Free Software Foundation August 24 1989 9 GAWK User Commands GAWK II//OO SSttaatteemmeennttss The input/output statements are as follows: cclloossee((_f_i_l_e_n_a_m_e)) close file (or pipe, see below). ggeettlliinnee set $$00 from next input record; set NNFF, NNRR, FFNNRR. ggeettlliinnee <<_f_i_l_e set $$00 from next record of _f_i_l_e; set NNFF. ggeettlliinnee _v_a_r set _v_a_r from next input record; set NNFF, FFNNRR. ggeettlliinnee _v_a_r <<_f_i_l_e set _v_a_r from next record of _f_i_l_e. nneexxtt 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 EENNDD block(s), if any, are executed. pprriinntt prints the current record. pprriinntt _e_x_p_r-_l_i_s_t prints expressions. pprriinntt _e_x_p_r-_l_i_s_t >>_f_i_l_e prints expressions on _f_i_l_e. pprriinnttff _f_m_t, _e_x_p_r-_l_i_s_t format and print. pprriinnttff _f_m_t, _e_x_p_r-_l_i_s_t >>_f_i_l_e format and print on _f_i_l_e. ssyysstteemm((_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 systems besides UNIX and GNU.) Other input/output redirections are also allowed. For pprriinntt and pprriinnttff, >>>>_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 || ggeett-- lliinnee pipes into ggeettlliinnee. GGeettlliinnee will return 0 on end of Free Software Foundation August 24 1989 10 GAWK User Commands GAWK file, and -1 on an error. TThhee _p_r_i_n_t_f SSttaatteemmeenntt The AWK versions of the pprriinnttff and sspprriinnttff (see below) func- tions accept the following conversion specification formats: %%cc An ASCII character. If the argument used for %%cc 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. %%dd A decimal number (the integer part). %%ii Just like %%dd. %%ee A floating point number of the form [[--]]dd..ddddddddddddEE[[++--]]dddd. %%ff A floating point number of the form [[--]]dddddd..dddddddddddd. %%gg Use ee or ff conversion, whichever is shorter, with nonsignificant zeros suppressed. %%oo An unsigned octal number (again, an integer). %%ss A character string. %%xx An unsigned hexadecimal number (an integer). %%XX Like %%xx, but using AABBCCDDEEFF instead of aabbccddeeff. %%%% 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 C library Free Software Foundation August 24 1989 11 GAWK User Commands GAWK pprriinnttff routines are not supported. However, they may be simulated by using the AWK concatenation operation to build up a format specification dynamically. SSppeecciiaall FFiillee NNaammeess When doing I/O redirection from either pprriinntt or pprriinnttff into a file, or via ggeettlliinnee 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). The filenames are: //ddeevv//ssttddiinn The standard input. //ddeevv//ssttddoouutt The standard output. //ddeevv//ssttddeerrrr The standard error output. //ddeevv//ffdd//_n The file denoted by the open file descriptor _n. These are particularly useful for error messages. For exam- ple: pprriinntt ""YYoouu bblleeww iitt!!"" >> ""//ddeevv//ssttddeerrrr"" whereas you would otherwise have to use pprriinntt ""YYoouu bblleeww iitt!!"" || ""ccaatt 11>>&&22"" These file names may also be used on the command line to name data files. NNuummeerriicc FFuunnccttiioonnss AWK has the following pre-defined arithmetic functions: aattaann22((_y,, _x)) returns the arctangent of _y/_x in radians. ccooss((_e_x_p_r)) returns the cosine in radians. eexxpp((_e_x_p_r)) the exponential function. iinntt((_e_x_p_r)) truncates to integer. Free Software Foundation August 24 1989 12 GAWK User Commands GAWK lloogg((_e_x_p_r)) the natural logarithm function. rraanndd(()) returns a random number between 0 and 1. ssiinn((_e_x_p_r)) returns the sine in radians. ssqqrrtt((_e_x_p_r)) the square root function. ssrraanndd((_e_x_p_r)) use _e_x_p_r as a new seed for the random number gen- erator. If no _e_x_p_r is provided, the time of day will be used. The return value is the previous seed for the random number generator. SSttrriinngg FFuunnccttiioonnss AWK has the following pre-defined string functions: ggssuubb((_r,, _s,, _t)) for each substring matching the regular expression _r in the string _t, substitute the string _s, and return the number of substitutions. If _t is not supplied, use $$00. iinnddeexx((_s,, _t)) returns the index of the string _t in the string _s, or 0 if _t is not present. lleennggtthh((_s)) returns the length of the string _s. mmaattcchh((_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 RRSSTTAARRTT and RRLLEENNGGTTHH. sspplliitt((_s,, _a,, _r)) splits the string _s into the array _a on the regu- lar expression _r, and returns the number of fields. If _r is omitted, FFSS is used instead. sspprriinnttff((_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, and returns the resulting string. ssuubb((_r,, _s,, _t)) this is just like ggssuubb, but only the first match- ing substring is replaced. Free Software Foundation August 24 1989 13 GAWK User Commands GAWK ssuubbssttrr((_s,, _i,, _n)) returns the _n-character substring of _s starting at _i. If _n is omitted, the rest of _s is used. ttoolloowweerr((_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 counterparts. Non- alphabetic characters are left unchanged. ttoouuppppeerr((_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 counterparts. Non- alphabetic characters are left unchanged. SSttrriinngg CCoonnssttaannttss 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: \\\\ A literal backslash. \\aa The ``alert'' character; usually the ASCII BEL character. \\bb backspace. \\ff form-feed. \\nn new line. \\rr carriage return. \\tt horizontal tab. \\vv vertical tab. \\xx_h_e_x _d_i_g_i_t_s The character represented by the string of hexade- cimal digits following the \\xx. 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. Free Software Foundation August 24 1989 14 GAWK User Commands GAWK The escape sequences may also be used inside constant regu- lar expressions (e.g., //[[ \\tt\\ff\\nn\\rr\\vv]]// matches whitespace characters). FFUUNNCCTTIIOONNSS Functions in AWK are defined as follows: ffuunnccttiioonn _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: ffuunnccttiioonn ff((pp,, qq,, aa,, bb)) {{ ## aa && bb aarree llooccaall .......... }} //aabbcc// {{ ...... ;; ff((11,, 22)) ;; ...... }} 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 ffuunncc may be used in place of ffuunnccttiioonn. EEXXAAMMPPLLEESS Print and sort the login names of all users: BBEEGGIINN {{ FFSS == ""::"" }} {{ pprriinntt $$11 || ""ssoorrtt"" }} Count lines in a file: {{ nnlliinneess++++ }} EENNDD {{ pprriinntt nnlliinneess }} Precede each line by its number in the file: Free Software Foundation August 24 1989 15 GAWK User Commands GAWK {{ pprriinntt FFNNRR,, $$00 }} Concatenate and line number (a variation on a theme): {{ pprriinntt NNRR,, $$00 }} SSEEEE AALLSSOO _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, published by the Free Software Foundation, 1989. SSYYSSTTEEMM VV RREELLEEAASSEE 44 CCOOMMPPAATTIIBBIILLIITTYY A primary goal for _g_a_w_k is compatibility 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 part of _a_w_k in System V Release 4. The --vv 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 BBEEGGIINN 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 BBEEGGIINN 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 behaviour. 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 ssrraanndd(()). The System V Release 4 version of UNIX _a_w_k has it return the seed it was using, to allow keeping track of random number sequences. Therefore ssrraanndd(()) in _g_a_w_k also returns its current seed. Other new features are: The use of multiple --ff options; the EENNVVIIRROONN array; the \\aa, and \\vv, \\xx escape sequences; the ttoolloowweerr and ttoouuppppeerr built-in functions; and the ANSI C conversion specifications in pprriinnttff. GGNNUU EEXXTTEENNSSIIOONNSS _G_a_w_k has some extensions to System V _a_w_k. They are described in this section. All the extensions described here can be disabled by compiling _g_a_w_k with --DDSSTTRRIICCTT, or by Free Software Foundation August 24 1989 16 GAWK User Commands GAWK invoking _g_a_w_k with the --cc option. If the underlying operat- ing system supports the //ddeevv//ffdd directory and corresponding files, then _g_a_w_k can be compiled with --DDNNOO__DDEEVV__FFDD to disable the special filename processing. The following features of _g_a_w_k are not available in System V _a_w_k. o+ The special file names available for I/O redirec- tion are not recognized. o+ The IIGGNNOORREECCAASSEE variable and its side-effects are not available. o+ No path search is performed for files named via the --ff option. Therefore the AAWWKKPPAATTHH environment variable is not special. o+ The --aa, --ee, --cc, --CC, and --VV command line options. The AWK book does not define the return value of the cclloossee function. _G_a_w_k's cclloossee 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 --cc option, if the _f_s argument to the --FF option is ``t'', then FFSS will be set to the tab character. Since this is a rather ugly special case, it is not the default behavior. BBUUGGSS The --FF option is not necessary given the command line vari- able assignment feature; it remains only for backwards com- patibility. There are now too many options. Fortunately, most of them are rarely needed. AAUUTTHHOORRSS 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 of Dalhousie University, with contributions from Arnold Robbins at Emory University, made _g_a_w_k compatible with the new version of UNIX _a_w_k. Free Software Foundation August 24 1989 17 GAWK User Commands GAWK AACCKKNNOOWWLLEEDDGGEEMMEENNTTSS Brian Kernighan of Bell Labs provided valuable assistance during testing and debugging. We thank him. Free Software Foundation August 24 1989 18