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Man Page for Gawk



NAME

       gawk - pattern scanning and processing language


SYNOPSIS

       gawk [ POSIX or GNU style options ] -f program-file [ -- ]
       file ...
       gawk [ POSIX or GNU style options ] [  --  ]  program-text
       file ...


DESCRIPTION

       Gawk  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  The  AWK  Programming  Language,  by Aho,
       Kernighan, and Weinberger, with  the  additional  features
       defined  in  the  System  V Release 4 version of UNIX awk.
       Gawk also provides some GNU-specific extensions.

       The command line consists of options to gawk  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

       Gawk  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,  gawk-specific  options  are
       supplied  via  arguments  to  the  -W option.  Multiple -W
       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 -W option.  Each -W option has
       a corresponding GNU style long option, as detailed  below.
       Arguments to GNU style long options are either joined with
       the option by an = sign, with no  intervening  spaces,  or
       they may be provided in the next command line argument.

       Gawk accepts the following options.

       -F fs
       --field-separator=fs
              Use  fs for the input field separator (the value of
              the FS predefined variable).

       -v var=val
       --assign=var=val
              Assign the value val, to the variable  var,  before
              execution  of  the  program  begins.  Such variable
              values are available to the BEGIN block of  an  AWK
              program.

       -f program-file
       --file=program-file
              Read  the AWK program source from the file program-
              file, instead of from the first command line  argu-
              ment.  Multiple -f (or --file) options may be used.

       -mf=NNN
       -mr=NNN
              Set various memory limits to the value NNN.  The  f
              flag  sets  the maximum number of fields, and the r
              flag sets the maximum record size.  These two flags
              and  the  -m  option  are  from  the AT&T Bell Labs
              research version of UNIX awk.  They are ignored  by
              gawk, since gawk has no pre-defined limits.
       -W compat
       --compat    Run  in  compatibility mode.  In compatibility
                   mode, gawk behaves identically  to  UNIX  awk;
                   none of the GNU-specific extensions are recog-
                   nized.  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.  Per the GNU
                   Coding Standards, these options cause an imme-
                   diate, successful exit.

       -W lint
       --lint      Provide  warnings  about  constructs  that are
                   dubious or non-portable to other AWK implemen-
                   tations.
       -W posix
       --posix     This  turns  on  compatibility  mode, with the
                   following 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=program-text
       --source=program-text
                   Use program-text 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 com-
                   mand  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 program-
                   text; no other options to -W  will  be  recog-
                   nized in the same argument.

       -W version
       --version   Print  version information for this particular
                   copy of gawk on the  error  output.   This  is
                   useful  mainly for knowing if the current copy
                   of gawk on your system  is  up  to  date  with
                   respect  to whatever the Free Software Founda-
                   tion is  distributing.   Per  the  GNU  Coding
                   Standards,  these  options cause an immediate,
                   successful exit.

       --          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.

       In compatibility mode, any other options  are  flagged  as
       illegal,  but are otherwise ignored.  In normal operation,
       as long as program text has been supplied, unknown options
       are  passed  on  to  the AWK program in the ARGV array for
       processing.  This is particularly useful for  running  AWK
       programs  via the ``#!'' executable interpreter mechanism.


AWK PROGRAM EXECUTION

       An AWK program consists of a  sequence  of  pattern-action
       statements and optional function definitions.

              pattern   { action statements }
              function name(parameter list)) { statements }

       Gawk  first  reads  the  program  source from the program-
       file(s) if specified, from arguments  to  -W  source=,  or
       from  the  first  non-option argument on the command line.
       The -f and -W source= options may be used  multiple  times
       on  the  command line.  Gawk will read the program text as
       if all the program-files and command line source texts had
       been  concatenated  together.  This is useful for building
       libraries of AWK functions, without having to include them
       in  each new AWK program that uses them.  It also provides
       the ability to mix library  functions  with  command  line
       programs.

       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.

       Gawk executes AWK programs in the following order.  First,
       all  variable  assignments specified via the -v option are
       performed.  Next, gawk compiles the program into an inter-
       nal  form.   Then,  gawk  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 line, gawk reads the standard input.

       If a filename on the command line has the form var=val  it
       is treated as a variable assignment. The variable var will
       be assigned the value val.  (This happens after any  BEGIN
       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  ARGV  is  empty
       (""), gawk skips over it.

       For  each  line  in  the  input,  gawk  tests to see if it
       matches any pattern in the AWK program.  For each  pattern
       that  the line matches, the associated action is executed.
       The patterns are tested in the order  they  occur  in  the
       program.

       Finally,  after  all the input is exhausted, gawk 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 dimensional arrays; arrays with
       multiple dimensions may be simulated.  Several pre-defined
       variables  are  set  as  a  program  runs;  these  will be
       described as needed and summarized below.

   Fields
       As each input line is read,  gawk  splits  the  line  into
       fields,  using  the  value of the FS variable as the field
       separator.  If FS is a single character, fields are  sepa-
       rated  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 gawk will split up the record using the  speci-
       fied 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
       position, $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 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 recom-
       puted, with the fields being separated  by  the  value  of
       OFS.  References to negative numbered fields cause a fatal
       error.

   Built-in Variables
       AWK's built-in variables are:


       ARGC        The number of command line arguments (does not
                   include   options  to  gawk,  or  the  program
                   source).

       ARGIND      The index in ARGV of the  current  file  being
                   processed.

       ARGV        Array  of command line arguments. The array is
                   indexed from  0  to  ARGC  -  1.   Dynamically
                   changing  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  gawk spawns via redirection or the sys-
                   tem() function.  (This may change in a  future
                   version of gawk.)

       ERRNO       If  a system error occurs either doing a redi-
                   rection for getline, during a  read  for  get-
                   line,  or  during  a  close(), then ERRNO will
                   contain a string describing the error.

       FIELDWIDTHS A white-space separated list  of  fieldwidths.
                   When set, gawk 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;
                   expect the semantics to change as gawk 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 ``-''.  However, FILENAME
                   is undefined inside the BEGIN block.

       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  functions  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 ini-
                   tial value of IGNORECASE is zero, so all regu-
                   lar  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 gawk.)  If RS is
                   set to the null string, then records are sepa-
                   rated  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.

       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 (expr, expr ...)   then  the  array  subscript  is  a
       string  consisting  of  the  concatenation of the (string)
       value of each expression, separated by the  value  of  the
       SUBSEP variable.  This facility is used to simulate multi-
       ply 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 val-
       ues.

       The  special  operator  in  may  be used in an if or while
       statement to see if an array has an index consisting of  a
       particular 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.  The delete  statement  may  also  be  used  to
       delete the entire contents of an array.

   Variable Typing And Conversion
       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 atof(3).  A number is converted
       to  a  string  by  using  the value of CONVFMT as a format
       string for sprintf(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  always  con-
       verted as integers.  Thus, given

              CONVFMT = "%2.2f"
              a = 12
              b = a ""

       the variable b has a string value of "12" and not "12.00".

       Gawk 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 gawk 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 missing, 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, however, this is not the case for lines ending in
       a  ``,'',  ``{'',  ``?'', ``:'', ``&&'', or ``||''.  Lines
       ending in do or else 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.

   Patterns
       AWK patterns may be one of the following:

              BEGIN
              END
              /regular expression/
              relational expression
              pattern && pattern
              pattern || pattern
              pattern ? pattern : pattern
              (pattern))
              ! pattern
              pattern1, pattern2

       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  written  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  /regular  expression/ 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 egrep(1), and are summarized below.

       A relational expression  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
       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  pattern1,  pattern2 form of an expression is called a
       range pattern.  It matches all input records starting with
       a  line  that  matches  pattern1,  and  continuing until a
       record that matches pattern2, inclusive. It does not  com-
       bine with any other sort of pattern expression.

   Regular Expressions
       Regular  expressions are the extended kind found in egrep.
       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.

       [abc...]   character class, matches any of the  characters
                  abc....

       [^abc...]  negated  character class, matches any character
                  except abc...  and newline.

       r1|r2      alternation: matches either r1 or r2.

       r1r2       concatenation: matches r1, and then r2.

       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 opera-
       tors,  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  (var  =
                   value))   and  operator-assignment  (the  other
                   forms) are supported.

       ?:          The C conditional  expression.  This  has  the
                   form  expr1 ? expr2 : expr3. If expr1 is true,
                   the value of the expression is  expr2,  other-
                   wise it is expr3.  Only one of expr2 and expr3
                   is 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/ ~ exp has the same meaning as
                   (($0  ~  /foo/)  ~  exp)).  This is usually not
                   what was intended.

       < >
       <= >=
       != ==       The regular relational operators.

       blank       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 (condition)) statement [ else statement ]
              while (condition)) statement
              do statement while (condition))
              for (expr1; expr2; expr3)) statement
              for (var in array)) statement
              break
              continue
              delete array[index]
              delete array
              exit [ expression ]
              { statements }

   I/O Statements
       The input/output statements are as follows:


       close(filename))       Close file (or pipe, see below).

       getline               Set  $0  from next input record; set
                             NF, NR, FNR.

       getline <file         Set $0 from next record of file; set
                             NF.

       getline var           Set  var from next input record; set
                             NF, FNR.

       getline var <file     Set var from next record of file.

       next                  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  END  block(s), if
                             any, are executed.

       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 pro-
                             gram. If the end of the  input  data
                             is  reached,  the  END  block(s), if
                             any, are executed.

       print                 Prints the current record.

       print expr-list       Prints expressions.  Each expression
                             is separated by the value of the OFS
                             variable. The output record is  ter-
                             minated  with  the  value of the ORS
                             variable.

       print expr-list >file Prints expressions  on  file.   Each
                             expression is separated by the value
                             of  the  OFS  variable.  The  output
                             record  is terminated with the value
                             of the ORS variable.

       printf fmt, expr-list Format and print.

       printf fmt, expr-list >file
                             Format and print on file.

       system(cmd-line))      Execute the  command  cmd-line,  and
                             return  the  exit status.  (This may
                             not be available on  non-POSIX  sys-
                             tems.)

       Other  input/output  redirections  are  also  allowed. For
       print and printf, >>file appends output to the file, while
       | command writes on a pipe.  In a similar fashion, command
       | getline pipes into getline.  The  getline  command  will
       return 0 on end of file, and -1 on an error.

   The printf Statement
       The  AWK  versions  of  the printf statement and sprintf()
       function (see below) accept the following conversion spec-
       ification 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
              nonsignificant 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.

       width  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.   This applies even to the non-numeric out-
              put formats.

       .prec  A number indicating the maximum width of strings or
              digits to the right of the decimal point.

       The  dynamic  width  and  prec  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().

   Special File Names
       When  doing  I/O  redirection  from either print or printf
       into a file, or via getline from a file,  gawk  recognizes
       certain  special  filenames  internally.   These filenames
       allow access  to  open  file  descriptors  inherited  from
       gawk's  parent process (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,  termi-
                   nated 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  sepa-
                   rated  with  blanks.   $1  is the value of the
                   getuid(2) system call, $2 is the value of  the
                   geteuid(2) system call, $3 is the value of the
                   getgid(2) system call, and $4 is the value  of
                   the  getegid(2) system call.  If there are any
                   additional fields,  they  are  the  group  IDs
                   returned by getgroups(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
                   descriptor n.

       These  are  particularly  useful  for  error messages. For
       example:

              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.

   Numeric Functions
       AWK has the following pre-defined arithmetic functions:


       atan2(y, x) returns the arctangent of y/x in radians.

       cos(expr))   returns the cosine in radians.

       exp(expr))   the exponential function.

       int(expr))   truncates to integer.

       log(expr))   the natural logarithm function.

       rand()      returns a random number between 0 and 1.

       sin(expr))   returns the sine in radians.

       sqrt(expr))  the square root function.

       srand(expr)) use  expr  as a new seed for the random number
                   generator. If no expr is provided, the time of
                   day  will  be  used.   The return value is the
                   previous 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
                               regular expression r in the string
                               t,  substitute  the  string s, and
                               return  the  number  of  substitu-
                               tions.   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
                               supplied.

       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.
                               The array a is cleared first.

       sprintf(fmt, expr-list)) prints expr-list according to fmt,
                               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 omit-
                               ted, the rest of s is used.

       tolower(str))            returns a copy of the string  str,
                               with all the upper-case characters
                               in str translated to their  corre-
                               sponding  lower-case counterparts.
                               Non-alphabetic characters are left
                               unchanged.

       toupper(str))            returns  a copy of the string str,
                               with all the lower-case characters
                               in  str translated to their corre-
                               sponding upper-case  counterparts.
                               Non-alphabetic characters are left
                               unchanged.

   Time Functions
       Since one of the primary uses of AWK programs is  process-
       ing  log  files  that contain time stamp information, gawk
       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(format, timestamp))
                 formats timestamp according to the specification
                 in format.  The timestamp should be of the  same
                 form  as returned by systime().  If timestamp 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 guar-
                 anteed to be available.  A public-domain version
                 of strftime(3) and a man page for it are shipped
                 with  gawk;  if  that  version was used to build
                 gawk, then all of the conversions  described  in
                 that man page are available to gawk.

   String Constants
       String  constants  in  AWK  are  sequences  of  characters
       enclosed between double quotes ("). Within  strings,  cer-
       tain escape sequences are recognized, as in C. These are:


       \\   A literal backslash.

       \a   The  ``alert'' character; usually the ASCII BEL char-
            acter.

       \b   backspace.

       \f   form-feed.

       \n   new line.

       \r   carriage return.

       \t   horizontal tab.

       \v   vertical tab.

       \xhex digits
            The character represented by the string of  hexadeci-
            mal  digits following the \x.  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.

       \ddd 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., /[ \t\f\n\r\v]/ matches whitespace
       characters).


FUNCTIONS

       Functions in AWK are defined as follows:

              function name(parameter list)) { statements }

       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:

              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  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.

       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

       egrep(1), getpid(2),  getppid(2),  getpgrp(2),  getuid(2),
       geteuid(2), getgid(2), getegid(2), getgroups(2)

       The  AWK  Programming  Language,  Alfred  V. Aho, Brian W.
       Kernighan, Peter J. Weinberger, Addison-Wesley, 1988. ISBN
       0-201-07981-X.

       The GAWK Manual, Edition 0.15, published by the Free Soft-
       ware Foundation, 1993.


POSIX COMPATIBILITY

       A primary goal for gawk is compatibility  with  the  POSIX
       standard,  as well as with the latest version of UNIX awk.
       To this end, gawk incorporates the following user  visible
       features  which are not described in the AWK book, but are
       part of awk in System V Release 4, and are  in  the  POSIX
       standard.

       The  -v option for assigning variables before program exe-
       cution starts is new.  The  book  indicates  that  command
       line  variable assignment happens when awk 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  before the BEGIN block was
       run.  Applications came to  depend  on  this  ``feature.''
       When  awk  was  changed  to  match its documentation, this
       option was added to accommodate applications that depended
       upon  the  old behavior.  (This feature was agreed upon by
       both the AT&T and GNU developers.)

       The -W option for implementation specific features is from
       the POSIX standard.

       When  processing  arguments,  gawk uses the special option
       ``--'' to signal the end of arguments.   In  compatibility
       mode,  it will warn about, but otherwise ignore, undefined
       options.  In normal operation, such arguments  are  passed
       on to the AWK program for it to process.

       The  AWK book does not define the return value of srand().
       The System V Release 4 version of UNIX awk (and the  POSIX
       standard)  has  it  return the seed it was using, to allow
       keeping  track  of  random  number  sequences.   Therefore
       srand() in gawk also returns its current seed.

       Other  new  features  are:  The use of multiple -f options
       (from MKS awk); the ENVIRON array; the \a, and  \v  escape
       sequences  (done  originally  in  gawk  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

       Gawk has some extensions to POSIX awk.  They are described
       in this section.  All the extensions described here can be
       disabled by invoking gawk with the -W compat option.

       The following features of gawk are not available in  POSIX
       awk.

              o The \x escape sequence.

              o The systime() and strftime() functions.

              o The special file names available for I/O redirec-
                tion are not recognized.

              o The ARGIND and ERRNO variables are not special.

              o The IGNORECASE variable and its side-effects  are
                not available.

              o The  FIELDWIDTHS  variable  and fixed width field
                splitting.

              o No path search is performed for files  named  via
                the -f option.  Therefore the AWKPATH environment
                variable is not special.

              o The use of next file to abandon processing of the
                current input file.

              o The use of delete array to delete the entire con-
                tents of an array.

       The AWK book does not  define  the  return  value  of  the
       close()  function.   Gawk's close() returns the value from
       fclose(3), or pclose(3), when  closing  a  file  or  pipe,
       respectively.

       When  gawk is invoked with the -W compat option, if the fs
       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 -W posix has been specified.


HISTORICAL FEATURES

       There  are  two features of historical AWK implementations
       that gawk 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
       standard,  and  gawk will issue a warning about its use if
       -W lint is specified on the command line.

       The other feature is the use of either the continue or the
       break  statements  outside the body of a while, for, or do
       loop.  Traditional AWK implementations have  treated  such
       usage as equivalent to the next statement.  Gawk will sup-
       port this usage if -W compat has been specified.


ENVIRONMENT VARIABLES

       If POSIXLY_CORRECT exists in the  environment,  then  gawk
       behaves  exactly  as  if --posix had been specified on the
       command line.  If --lint has  been  specified,  gawk  will
       issue a warning message to this effect.


BUGS

       The  -F  option  is  not  necessary given the command line
       variable assignment feature; it remains only for backwards
       compatibility.

       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 gawk than you would get
       on a system without those  files.   When  gawk  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 differ-
       ent open files.  Caveat Emptor.


VERSION INFORMATION

       This man page documents gawk, version 2.15.

       Starting with the 2.15 version of gawk, the  -c,  -V,  -C,
       -a,  and -e options of the 2.11 version are no longer rec-
       ognized.  This fact will not even  be  documented  in  the
       manual page for the next major version.


AUTHORS

       The  original  version of UNIX awk 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 gawk, to be compatible with the original ver-
       sion of awk distributed in  Seventh  Edition  UNIX.   John
       Woods  contributed  a number of bug fixes.  David Trueman,
       with  contributions  from  Arnold   Robbins,   made   gawk
       compatible  with the new version of UNIX awk.  Arnold Rob-
       bins is the current maintainer.

       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.  The port to OS/2 was done by
       Kai Uwe Rommel, with contributions and  help  from  Darrel
       Hankerson.


BUG REPORTS

       If  you find a bug in gawk, please send electronic mail to
       bug-gnu-,  with  a  carbon  copy   to
       .  Please include your operating sys-
       tem and its revision, the version of gawk, what C compiler
       you  used  to compile it, and a test program and data that
       are as small as possible for reproducing the problem.

       Before sending a bug report, please do two things.  First,
       verify  that  you  have  the latest version of gawk.  Many
       bugs (usually subtle ones) are fixed at each release,  and
       if  your's  is  out  of date, the problem may already have
       been solved.  Second, please read this man  page  and  the
       reference  manual carefully to be sure that what you think
       is a bug really is, instead of just a quirk  in  the  lan-
       guage.


ACKNOWLEDGEMENTS

       Brian  Kernighan of Bell Labs provided valuable assistance
       during testing and debugging.  We thank him.


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