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GAWK(1) Utility Commands GAWK(1) NNAAMMEE gawk - pattern scanning and processing language SSYYNNOOPPSSIISS ggaawwkk [ POSIX or GNU style options ] --ff _p_r_o_g_r_a_m_-_f_i_l_e [ ---- ] file ... ggaawwkk [ POSIX or GNU style options ] [ ---- ] _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 pro- gramming language. It conforms to the definition of the language in the POSIX 1003.2 Command Language And Utili- ties 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 System 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 --ff or ----ffiillee options), and values to be made available in the AARRGGCC and AARRGGVV pre-defined AWK variables. OOPPTTIIOONNSS _G_a_w_k options may be either the traditional POSIX one let- ter 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 fea- tures. 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 supplied via arguments to the --WW option. Multiple --WW options may be supplied, or multiple arguments may be sup- plied together if they are separated by commas, or enclosed in quotes and separated by white space. Case is ignored in arguments to the --WW option. Each --WW option has a corresponding GNU style long option, as detailed below. _G_a_w_k accepts the following options. --FF _f_s ----ffiieelldd--sseeppaarraattoorr==_f_s Use _f_s for the input field separator (the value of the FFSS predefined variable). --vv _v_a_r==_v_a_l ----aassssiiggnn==_v_a_r==_v_a_l Assign the value _v_a_l, to the variable _v_a_r, before execution of the program begins. Such variable values are available to the BBEEGGIINN block of an AWK program. Free Software Foundation Apr 15 1993 1 GAWK(1) Utility Commands GAWK(1) --ff _p_r_o_g_r_a_m_-_f_i_l_e ----ffiillee==_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 argu- ment. Multiple --ff (or ----ffiillee) options may be used. --WW ccoommppaatt ----ccoommppaatt 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 recog- nized. See GGNNUU EEXXTTEENNSSIIOONNSS, below, for more information. --WW ccooppyylleefftt --WW ccooppyyrriigghhtt ----ccooppyylleefftt ----ccooppyyrriigghhtt Print the short version of the GNU copyright information message on the error output. --WW hheellpp --WW uussaaggee ----hheellpp ----uussaaggee Print a relatively short summary of the avail- able options on the error output. --WW lliinntt ----lliinntt Provide warnings about constructs that are dubious or non-portable to other AWK implemen- tations. --WW ppoossiixx ----ppoossiixx This turns on _c_o_m_p_a_t_i_b_i_l_i_t_y mode, with the following additional restrictions: o \\xx escape sequences are not recognized. o The synonym ffuunncc for the keyword ffuunnccttiioonn is not recognized. o The operators **** and ****== cannot be used in place of ^^ and ^^==. --WW ssoouurrccee==_p_r_o_g_r_a_m_-_t_e_x_t ----ssoouurrccee==_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 --ff and ----ffiillee options) with source code entered on the com- mand line. It is intended primarily for medium to large size AWK programs used in shell scripts. The --WW ssoouurrccee== form of this option uses the rest of the command line argument for _p_r_o_g_r_a_m_- _t_e_x_t; no other options to --WW will be recog- nized in the same argument. Free Software Foundation Apr 15 1993 2 GAWK(1) Utility Commands GAWK(1) --WW vveerrssiioonn ----vveerrssiioonn 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 Founda- tion is distributing. ---- 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 other- wise ignored. AAWWKK PPRROOGGRRAAMM EEXXEECCUUTTIIOONN 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 argu- ment on the command line. The --ff option may be used mul- tiple times on the command line. _G_a_w_k will read the pro- gram text as if all the _p_r_o_g_r_a_m_-_f_i_l_es had been concate- nated together. This is useful for building libraries of AWK functions, without having 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, spec- ify //ddeevv//ttttyy as one of the _p_r_o_g_r_a_m_-_f_i_l_es, type your pro- gram, 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 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 --vv option are performed. Then, _g_a_w_k 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 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 BBEEGGIINN Free Software Foundation Apr 15 1993 3 GAWK(1) Utility Commands GAWK(1) block(s) have been run.) Command line variable assignment 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. If the value of a particular element of AARRGGVV 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 patterns 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 EENNDD block(s) (if any). 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, or both, depending upon how they are used. AWK also has one dimension arrays; multiply dimensioned arrays may be simulated. Several pre-defined variables are set 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 sepa- rated 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. If the FFIIEELLDDWWIIDDTTHHSS 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 speci- fied widths. The value of FFSS is ignored. Assigning a new value to FFSS overrides the use of FFIIEELLDDWWIIDDTTHHSS, and restores the default behavior. Each field in the input line may be referenced by its position, $$11, $$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 Free Software Foundation Apr 15 1993 4 GAWK(1) Utility Commands GAWK(1) 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 recom- puted, 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). AARRGGIINNDD The index in AARRGGVV of the current file being processed. 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. CCOONNVVFFMMTT The conversion format for numbers, ""%%..66gg"", by default. EENNVVIIRROONN 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., 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 ssyyss-- tteemm(()) function. (This may change in a future version of _g_a_w_k.) EERRRRNNOO If a system error occurs either doing a redi- rection for ggeettlliinnee, during a read for ggeett-- lliinnee, or during a cclloossee, then EERRRRNNOO will con- tain a string describing the error. FFIIEELLDDWWIIDDTTHHSS 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 FFSS variable as the field separator. The fixed field width facility is still experimental; expect the semantics to change as _g_a_w_k evolves over time. FFIILLEENNAAMMEE The name of the current input file. If no Free Software Foundation Apr 15 1993 5 GAWK(1) Utility Commands GAWK(1) 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 operations. 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 ini- tial value of IIGGNNOORREECCAASSEE is zero, so all regu- lar 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. OOFFSS The output field separator, a blank by default. OORRSS The output record separator, by default a new- line. RRSS The input record separator, by default a new- line. RRSS 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 RRSS is set to the null string, then records are sepa- rated 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. Free Software Foundation Apr 15 1993 6 GAWK(1) Utility Commands GAWK(1) SSUUBBSSEEPP The character used to separate multiple sub- scripts 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 consisting of the concatenation of the (string) value of each expression, separated by the value of the SSUUBBSSEEPP variable. This facility is used to simulate multi- ply 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 val- ues. The special operator iinn may be used in an iiff or wwhhiillee statement to see if an array has an index consisting of a particular value. iiff ((vvaall iinn aarrrraayy)) pprriinntt aarrrraayy[[vvaall]] If the array has multiple subscripts, use ((ii,, jj)) iinn aarrrraayy. 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 AAnndd CCoonnvveerrssiioonn Variables and fields may be (floating point) numbers, or strings, or both. How the value of a variable is inter- preted 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 conver- sion is accomplished using _a_t_o_f(3). A number is converted to a string by using the value of CCOONNVVFFMMTT as a format string for _s_p_r_i_n_t_f(3), with the numeric value of the vari- able as the argument. However, even though all numbers in AWK are floating-point, integral values are _a_l_w_a_y_s con- verted as integers. Thus, given Free Software Foundation Apr 15 1993 7 GAWK(1) Utility Commands GAWK(1) CCOONNVVFFMMTT == ""%%22..22ff"" aa == 1122 bb == aa """" the variable bb has a value of ""1122"" and not ""1122..0000"". _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 numeri- cally. Otherwise, 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 comparison 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). 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 missing, 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, however, this is not the case for lines ending in a ``,'', ``{'', ``?'', ``:'', ``&&'', or ``||''. Lines ending in ddoo or eellssee also have their statements automati- cally continued on the following line. In other cases, a line can be continued 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. 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 Free Software Foundation Apr 15 1993 8 GAWK(1) Utility Commands GAWK(1) _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 written 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 state- ment is executed for each input line that matches the reg- ular 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 expres- sions. 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 combin- ing more primitive pattern expressions. As in most lan- guages, 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 com- bine with any 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. Free Software Foundation Apr 15 1993 9 GAWK(1) Utility Commands GAWK(1) .. 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 opera- tors, 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)) 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, other- wise 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. Free Software Foundation Apr 15 1993 10 GAWK(1) Utility Commands GAWK(1) ~~ !!~~ Regular expression match, negated match. NNOOTTEE:: Do not use a constant regular expression (//ffoooo//) on the left-hand side of a ~~ or !!~~. Only use one on the right-hand side. The expression //ffoooo// ~~ _e_x_p has the same meaning as (((($$00 ~~ //ffoooo//)) ~~ _e_x_p)). This is usually _n_o_t what was intended. << >> <<== >>== !!== ==== The regular relational operators. _b_l_a_n_k String concatenation. ++ -- Addition and subtraction. ** // %% Multiplication, division, and modulus. ++ -- !! Unary plus, unary minus, and logical negation. ^^ Exponentiation (**** may also be used, and ****== for the assignment operator). ++++ ---- Increment and decrement, both prefix and post- fix. $$ Field reference. 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 }} 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. Free Software Foundation Apr 15 1993 11 GAWK(1) Utility Commands GAWK(1) 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 pro- gram. If the end of the input data is reached, the EENNDD block(s), if any, are executed. nneexxtt ffiillee Stop processing the current input file. The next input record read comes from the next input file. FFIILLEENNAAMMEE is updated, FFNNRR is reset to 1, and processing starts over with the first pattern in the AWK pro- gram. 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 non-POSIX sys- tems.) 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 || ggeettlliinnee pipes into ggeettlliinnee. GGeettlliinnee will return 0 on end of file, and -1 on an error. TThhee _p_r_i_n_t_f SSttaatteemmeenntt The AWK versions of the pprriinnttff statement and sspprriinnttff(()) function (see below) accept the following conversion spec- ification 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 Free Software Foundation Apr 15 1993 12 GAWK(1) Utility Commands GAWK(1) 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 ANSI C pprriinnttff(()) routines are supported. A ** in place of either the wwiiddtthh or pprreecc specifications will cause their values to be taken from the argument list to pprriinnttff or sspprriinnttff(()). 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 process (usually the shell). Other special filenames provide access information about the running ggaawwkk process. The filenames are: //ddeevv//ppiidd Reading this file returns the process ID of the current process, in decimal, terminated Free Software Foundation Apr 15 1993 13 GAWK(1) Utility Commands GAWK(1) with a newline. //ddeevv//ppppiidd Reading this file returns the parent process ID of the current process, in decimal, termi- nated with a newline. //ddeevv//ppggrrppiidd Reading this file returns the process group ID of the current process, in decimal, terminated with a newline. //ddeevv//uusseerr Reading this file returns a single record ter- minated with a newline. The fields are sepa- rated with blanks. $$11 is the value of the _g_e_t_u_i_d(2) system call, $$22 is the value of the _g_e_t_e_u_i_d(2) system call, $$33 is the value of the _g_e_t_g_i_d(2) system call, and $$44 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.) //ddeevv//ssttddiinn The standard input. //ddeevv//ssttddoouutt The standard output. //ddeevv//ssttddeerrrr The standard error output. //ddeevv//ffdd//_n The file associated with the open file descriptor _n. These are particularly useful for error messages. For example: 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 Apr 15 1993 14 GAWK(1) Utility Commands GAWK(1) 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 generator. 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 substitu- tions. If _t is not supplied, use $$00. iinnddeexx((_s,, _t)) returns the index of the string _t in the string _s, or 0 if _t is not present. lleennggtthh((_s)) returns the length of the string _s, or the length of $$00 if _s is not supplied. 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 regular 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)) just like ggssuubb(()), but only the first matching substring is replaced. ssuubbssttrr((_s,, _i,, _n)) returns the _n-character substring of _s starting at _i. If _n is omit- ted, the rest of _s is used. ttoolloowweerr((_s_t_r)) returns a copy of the string _s_t_r, Free Software Foundation Apr 15 1993 15 GAWK(1) Utility Commands GAWK(1) with all the upper-case characters in _s_t_r translated to their corre- sponding 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 corre- sponding upper-case counterparts. Non-alphabetic characters are left unchanged. TTiimmee FFuunnccttiioonnss Since one of the primary uses of AWK programs is process- ing log files that contain time stamp information, _g_a_w_k provides the following two functions for obtaining time stamps and formatting them. ssyyssttiimmee(()) returns the current time of day as the number of seconds since the Epoch (Midnight UTC, January 1, 1970 on POSIX systems). ssttrrffttiimmee((_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 ssyyssttiimmee(()). If _t_i_m_e_s_t_a_m_p is missing, the current time of day is used. See the specification for the ssttrrffttiimmee(()) function in ANSI C for the format conversions that are guar- anteed 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_. SSttrriinngg CCoonnssttaannttss String constants in AWK are sequences of characters enclosed between double quotes (""). Within strings, cer- tain _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 char- acter. \\bb backspace. \\ff form-feed. \\nn new line. Free Software Foundation Apr 15 1993 16 GAWK(1) Utility Commands GAWK(1) \\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 hexadeci- mal digits following the \\xx. As in ANSI C, all fol- lowing hexadecimal digits are considered part of the escape sequence. (This feature should tell us some- thing 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 reg- ular 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 lan- guage, the provision for local variables is rather clumsy: They are declared as extra parameters in the parameter 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 inter- vening white space. This is to avoid a syntactic ambigu- ity with the concatenation operator. This restriction does not apply to the built-in functions listed above. Free Software Foundation Apr 15 1993 17 GAWK(1) Utility Commands GAWK(1) 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 $$11 || ""ssoorrtt"" }} Count lines in a file: {{ nnlliinneess++++ }} EENNDD {{ pprriinntt nnlliinneess }} Precede each line by its number in the file: {{ pprriinntt FFNNRR,, $$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. Kernighan, 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 Soft- ware Foundation, 1993. PPOOSSIIXX CCOOMMPPAATTIIBBIILLIITTYY 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 part of _a_w_k in System V Release 4, and are in the POSIX standard. The --vv option for assigning variables before program exe- cution 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 Free Software Foundation Apr 15 1993 18 GAWK(1) Utility Commands GAWK(1) upon the old behavior. (This feature was agreed upon by both the AT&T and GNU developers.) The --WW 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 ssrraanndd(()). 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 ssrraanndd(()) in _g_a_w_k also returns its current seed. Other new features are: The use of multiple --ff options (from MKS _a_w_k); the EENNVVIIRROONN array; the \\aa, and \\vv escape sequences (done originally in _g_a_w_k and fed back into AT&T's); the ttoolloowweerr(()) and ttoouuppppeerr(()) built-in functions (from AT&T); and the ANSI C conversion specifications in pprriinnttff (done first in AT&T's version). GGNNUU EEXXTTEENNSSIIOONNSS _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 --WW ccoommppaatt option. The following features of _g_a_w_k are not available in POSIX _a_w_k. o The \\xx escape sequence. o The ssyyssttiimmee(()) and ssttrrffttiimmee(()) functions. o The special file names available for I/O redirec- tion are not recognized. o The AARRGGIINNDD and EERRRRNNOO variables are not special. o The IIGGNNOORREECCAASSEE variable and its side-effects are not available. o The FFIIEELLDDWWIIDDTTHHSS variable and fixed width field splitting. o No path search is performed for files named via the --ff option. Therefore the AAWWKKPPAATTHH environment variable is not special. o The use of nneexxtt ffiillee to abandon processing of the current input file. The AWK book does not define the return value of the Free Software Foundation Apr 15 1993 19 GAWK(1) Utility Commands GAWK(1) 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 --WW ccoommppaatt 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. This behavior also does not occur if --WWppoossiixx has been specified. HHIISSTTOORRIICCAALL FFEEAATTUURREESS There are two features of historical AWK implementations that _g_a_w_k supports. First, it is possible to call the lleennggtthh(()) built-in function not only with no argument, but even without parentheses! Thus, aa == lleennggtthh is the same as either of aa == lleennggtthh(()) aa == lleennggtthh(($$00)) This feature is marked as ``deprecated'' in the POSIX standard, and _g_a_w_k will issue a warning about its use if --WWlliinntt is specified on the command line. The other feature is the use of the ccoonnttiinnuuee statement outside the body of a wwhhiillee, ffoorr, or ddoo loop. Traditional AWK implementations have treated such usage as equivalent to the nneexxtt statement. _G_a_w_k will support this usage if --WWppoossiixx has not been specified. BBUUGGSS The --FF option is not necessary given the command line variable assignment feature; it remains only for backwards compatibility. If your system actually has support for //ddeevv//ffdd and the associated //ddeevv//ssttddiinn, //ddeevv//ssttddoouutt, and //ddeevv//ssttddeerrrr 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 //ddeevv//ssttddoouutt, while on a system with those files, the output is actually to differ- ent open files. Caveat Emptor. VVEERRSSIIOONN IINNFFOORRMMAATTIIOONN This man page documents _g_a_w_k, version 2.15. Starting with the 2.15 version of _g_a_w_k, the --cc, --VV, --CC, --aa, and --ee options of the 2.11 version are no longer rec- ognized. Free Software Foundation Apr 15 1993 20 GAWK(1) Utility Commands GAWK(1) 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 ver- sion of _a_w_k distributed in Seventh Edition UNIX. John Woods contributed a number of bug fixes. David Trueman, with contributions from Arnold Robbins, made _g_a_w_k compati- ble with the new version of UNIX _a_w_k. The initial DOS port was done by Conrad Kwok and Scott Garfinkle. Scott Deifik is the current DOS maintainer. Pat Rankin did the port to VMS, and Michal Jaegermann did the port to the Atari ST. AACCKKNNOOWWLLEEDDGGEEMMEENNTTSS Brian Kernighan of Bell Labs provided valuable assistance during testing and debugging. We thank him. Free Software Foundation Apr 15 1993 21