awk



GAWK(1)                        Utility Commands                        GAWK(1)




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 ...

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


DESCRIPTION

       Gawk  is  the  GNU Project’s implementation of the AWK programming lan-
       guage.  It conforms to the definition of  the  language  in  the  POSIX
       1003.2  Command  Language And Utilities Standard.  This version in turn
       is based on the description in The AWK Programming  Language,  by  Aho,
       Kernighan,  and  Weinberger,  with the additional features found in the
       System V Release 4 version of UNIX awk.  Gawk also provides more recent
       Bell  Laboratories  awk extensions, and a number of GNU-specific exten-
       sions.

       Pgawk is the profiling version of gawk.  It is identical in  every  way
       to  gawk,  except  that  programs run more slowly, and it automatically
       produces an execution profile in the file awkprof.out when  done.   See
       the --profile option, below.

       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.


OPTION FORMAT

       Gawk options may be either traditional POSIX one letter options, or GNU
       style long options.  POSIX options start with a single “-”, while  long
       options  start  with “--”.  Long options are provided for both GNU-spe-
       cific features and for POSIX-mandated features.

       Following the POSIX standard, gawk-specific options  are  supplied  via
       arguments  to  the -W option.  Multiple -W options may be supplied Each
       -W option has a corresponding long option, as  detailed  below.   Argu-
       ments  to  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.  Long options may be abbreviated, as long as the abbre-
       viation remains unique.


OPTIONS

       Gawk accepts the following options, listed alphabetically.

       -F fs
       --field-separator fs
              Use fs for the input field separator (the value of the FS prede-
              fined 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  argument.   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 Bell Labo-
              ratories research version of UNIX  awk.   They  are  ignored  by
              gawk, since gawk has no pre-defined limits.

       -W compat
       -W traditional
       --compat
       --traditional
              Run  in compatibility mode.  In compatibility mode, gawk behaves
              identically to UNIX awk; none of the GNU-specific extensions are
              recognized.   The  use  of  --traditional  is preferred over the
              other forms of this option.  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 standard output and exit successfully.

       -W dump-variables[=file]
       --dump-variables[=file]
              Print a sorted list of global variables, their types  and  final
              values  to file.  If no file is provided, gawk uses a file named
              awkvars.out in the current directory.
              Having a list of all the global variables is a good way to  look
              for  typographical  errors in your programs.  You would also use
              this option if you have a large program with a lot of functions,
              and  you want to be sure that your functions don’t inadvertently
              use global variables that you meant to be  local.   (This  is  a
              particularly  easy  mistake  to  make with simple variable names
              like i, j, and so on.)

       -W help
       -W usage
       --help
       --usage
              Print a relatively short summary of the available options on the
              standard  output.   (Per the GNU Coding Standards, these options
              cause an immediate, successful exit.)

       -W lint[=value]
       --lint[=value]
              Provide warnings about  constructs  that  are  dubious  or  non-
              portable  to  other AWK implementations.  With an optional argu-
              ment of fatal, lint warnings become fatal errors.  This  may  be
              drastic, but its use will certainly encourage the development of
              cleaner AWK programs.  With an  optional  argument  of  invalid,
              only warnings about things that are actually invalid are issued.
              (This is not fully implemented yet.)

       -W lint-old
       --lint-old
              Provide warnings about constructs that are not portable  to  the
              original version of Unix awk.

       -W gen-po
       --gen-po
              Scan  and  parse  the AWK program, and generate a GNU .po format
              file on standard output with entries for all localizable strings
              in  the  program.   The program itself is not executed.  See the
              GNU gettext distribution for more information on .po files.

       -W non-decimal-data
       --non-decimal-data
              Recognize octal and hexadecimal values in input data.  Use  this
              option with great caution!

       -W posix
       --posix
              This  turns on compatibility mode, with the following additional
              restrictions:

              · \x escape sequences are not recognized.

              · Only space and tab act as field separators when FS is set to a
                single space, newline does not.

              · You cannot continue lines after ?  and :.

              · The synonym func for the keyword function is not recognized.

              · The  operators ** and **= cannot be used in place of ^ and ^=.

              · The fflush() function is not available.

       -W profile[=prof_file]
       --profile[=prof_file]
              Send profiling data to prof_file.  The default  is  awkprof.out.
              When  run with gawk, the profile is just a “pretty printed” ver-
              sion of the program.  When run with pgawk, the profile  contains
              execution  counts  of  each statement in the program in the left
              margin and function call counts for each user-defined  function.

       -W re-interval
       --re-interval
              Enable  the  use  of  interval expressions in regular expression
              matching (see Regular Expressions, below).  Interval expressions
              were not traditionally available in the AWK language.  The POSIX
              standard added them, to make awk and egrep consistent with  each
              other.   However, their use is likely to break old AWK programs,
              so gawk only provides them  if  they  are  requested  with  this
              option, or when --posix is specified.

       -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 command line.
              It is intended primarily for medium to large AWK  programs  used
              in shell scripts.

       -W version
       --version
              Print  version  information  for this particular copy of gawk on
              the standard 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 Foundation is distributing.   This
              is  also  useful when reporting bugs.  (Per the GNU Coding Stan-
              dards, these options cause an immediate, successful exit.)

       --     Signal the end of options. This is useful to allow further argu-
              ments  to  the  AWK program itself to start with a “-”.  This is
              mainly for consistency with the argument parsing convention used
              by most other POSIX programs.
       In  compatibility  mode,  any other options are flagged as invalid, 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  speci-
       fied, from arguments to --source, or from the first non-option argument
       on the command line.  The -f and --source options may be used  multiple
       times  on  the command line.  Gawk reads 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/local/share/awk".   (The  actual
       directory  may  vary, depending upon how gawk was built and installed.)
       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 com-
       piles  the program into an internal 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 val-
       ues to the variables AWK uses to  control  how  input  is  broken  into
       fields  and records.  It is also useful for controlling state if multi-
       ple 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 record in the input, gawk tests to see if it matches any pat-
       tern in the AWK program.  For each pattern that the record 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, RECORDS 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.
   Records
       Normally, records are separated by newline characters.  You can control
       how  records are separated by assigning values to the built-in variable
       RS.  If RS is any single character, that character  separates  records.
       Otherwise,  RS is a regular expression.  Text in the input that matches
       this regular expression separates the record.  However, in  compatibil-
       ity mode, only the first character of its string value is used for sep-
       arating records.  If RS is set to the null  string,  then  records  are
       separated  by blank lines.  When RS is set to the null string, the new-
       line character always acts as a field separator, in addition  to  what-
       ever value FS may have.
   Fields
       As each input record is read, gawk splits the record into fields, using
       the value of the FS variable as the field separator.  If FS is a single
       character,  fields  are separated by that character.  If FS is the null
       string, then each individual character becomes a separate field.   Oth-
       erwise, FS is expected to be a full regular expression.  In the special
       case that FS is a single space, fields are separated by runs of  spaces
       and/or  tabs  and/or  newlines.   (But  see  the discussion of --posix,
       below).  NOTE: The value of IGNORECASE (see  below)  also  affects  how
       fields  are  split when FS is a regular expression, and how records are
       separated when RS is a regular expression.
       If the FIELDWIDTHS variable is set to a space separated  list  of  num-
       bers,  each  field  is expected to have fixed width, and gawk splits up
       the record using the specified widths.  The value  of  FS  is  ignored.
       Assigning  a  new  value  to  FS  overrides the use of FIELDWIDTHS, and
       restores the default behavior.
       Each field in the input record may be referenced by its  position,  $1,
       $2,  and so on.  $0 is the whole record.  Fields need not be referenced
       by constants:
              n = 5
              print $n
       prints the fifth field in the input record.
       The variable NF is set to the total  number  of  fields  in  the  input
       record.
       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) increases the value of NF, creates any intervening fields with the
       null string as their value, and causes 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.   Decrementing  NF
       causes  the  values  of  fields  past the new value to be lost, and the
       value of $0 to be recomputed, with the fields being  separated  by  the
       value of OFS.
       Assigning  a  value  to an existing field causes the whole record to be
       rebuilt when $0 is referenced.  Similarly,  assigning  a  value  to  $0
       causes the record to be resplit, creating new values for the fields.
   Built-in Variables
       Gawk’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.
       BINMODE     On non-POSIX systems, specifies use of  “binary”  mode  for
                   all  file  I/O.  Numeric values of 1, 2, or 3, specify that
                   input files, output  files,  or  all  files,  respectively,
                   should  use binary I/O.  String values of "r", or "w" spec-
                   ify that input files, or output files, respectively, should
                   use binary I/O.  String values of "rw" or "wr" specify that
                   all files should use binary I/O.  Any other string value is
                   treated as "rw", but generates a warning message.
       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., ENVI-
                   RON["HOME"] might be /home/arnold).   Changing  this  array
                   does not affect the environment seen by programs which gawk
                   spawns via redirection or the system() function.
       ERRNO       If a system error occurs either  doing  a  redirection  for
                   getline,  during  a  read for getline, or during a close(),
                   then ERRNO will contain a string describing the error.  The
                   value is subject to translation in non-English locales.
       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 separa-
                   tor.
       FILENAME    The name of the current input file.  If no files are speci-
                   fied  on  the  command  line, the value of FILENAME is “-”.
                   However, FILENAME  is  undefined  inside  the  BEGIN  block
                   (unless set by getline).
       FNR         The input record number in the current input file.
       FS          The input field separator, a space by default.  See Fields,
                   above.
       IGNORECASE  Controls the case-sensitivity of all regular expression and
                   string  operations.   If  IGNORECASE  has a non-zero value,
                   then string comparisons  and  pattern  matching  in  rules,
                   field splitting with FS, record separating with RS, regular
                   expression matching  with  ~  and  !~,  and  the  gensub(),
                   gsub(), index(), match(), split(), and sub() built-in func-
                   tions all ignore case when doing regular expression  opera-
                   tions.  NOTE: Array subscripting is not affected.  However,
                   the asort() and asorti() functions are affected.
                   Thus, if IGNORECASE is not equal to zero, /aB/ matches  all
                   of the strings "ab", "aB", "Ab", and "AB".  As with all AWK
                   variables, the initial value of IGNORECASE is zero, so  all
                   regular expression and string operations are normally case-
                   sensitive.  Under Unix, the full ISO 8859-1 Latin-1 charac-
                   ter  set is used when ignoring case.  As of gawk 3.1.4, the
                   case equivalencies are fully locale-aware, based on  the  C
                   <ctype.h> facilities such as isalpha(), and tolupper().
       LINT        Provides  dynamic  control of the --lint option from within
                   an AWK program.  When true, gawk prints lint warnings. When
                   false,  it  does  not.   When  assigned  the  string  value
                   "fatal", lint warnings become fatal  errors,  exactly  like
                   --lint=fatal.  Any other true value just prints warnings.
       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 space by default.
       ORS         The output record separator, by default a newline.
       PROCINFO    The  elements  of  this array provide access to information
                   about the running AWK program.  On some systems, there  may
                   be  elements  in  the  array, "group1" through "groupn" for
                   some n, which is the number of  supplementary  groups  that
                   the  process  has.   Use  the in operator to test for these
                   elements.  The following  elements  are  guaranteed  to  be
                   available:
                   PROCINFO["egid"]   the value of the getegid(2) system call.
                   PROCINFO["euid"]   the value of the geteuid(2) system call.
                   PROCINFO["FS"]     "FS"  if  field  splitting with FS is in
                                      effect, or "FIELDWIDTHS" if field split-
                                      ting with FIELDWIDTHS is in effect.
                   PROCINFO["gid"]    the  value of the getgid(2) system call.
                   PROCINFO["pgrpid"] the process group ID of the current pro-
                                      cess.
                   PROCINFO["pid"]    the process ID of the current process.
                   PROCINFO["ppid"]   the  parent  process  ID  of the current
                                      process.
                   PROCINFO["uid"]    the value of the getuid(2) system  call.
                   PROCINFO["version"]
                                      The  version of gawk.  This is available
                                      from version 3.1.4 and later.
       RS          The input record separator, by default a newline.
       RT          The record terminator.  Gawk sets RT to the input text that
                   matched  the  character  or regular expression specified by
                   RS.
       RSTART      The index of the first character matched by match();  0  if
                   no  match.   (This  implies that character indices start at
                   one.)
       RLENGTH     The length of the string  matched  by  match();  -1  if  no
                   match.
       SUBSEP      The character used to separate multiple subscripts in array
                   elements, by default "\034".
       TEXTDOMAIN  The text domain of the AWK program; used to find the local-
                   ized translations for the program’s strings.
   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 multiply dimensioned
       arrays.  For example:
              i = "A"; j = "B"; k = "C"
              x[i, j, k] = "hello, world\n"
       assigns the string "hello, world\n" to the element of the array x which
       is indexed by the string "A\034B\034C".  All arrays in AWK are associa-
       tive, i.e. indexed by string values.
       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, just by specifying the array name without a subscript.
   Variable Typing And Conversion
       Variables and fields may be (floating point) numbers,  or  strings,  or
       both.  How the value of a variable is interpreted depends upon its con-
       text.  If used in a numeric expression, it will be treated as a number,
       if used as a string it will be treated as a string.
       To force a variable to be treated as a number, add 0 to it; to force it
       to be treated as a string, concatenate it with the null string.
       When a string must be converted to a number, the conversion  is  accom-
       plished  using  strtod(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 variable 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 numerically.  Otherwise, the numeric value is converted to  a
       string and a string comparison is performed.  Two strings are compared,
       of course, as strings.  Note that the POSIX standard applies  the  con-
       cept  of  “numeric  string” everywhere, even to string constants.  How-
       ever, this is clearly incorrect, and gawk does not  do  this.   (Fortu-
       nately, this is fixed in the next version of the standard.)
       Note that string constants, such as "57", are not numeric strings, they
       are string constants.  The idea of “numeric  string”  only  applies  to
       fields,  getline  input,  FILENAME, ARGV elements, ENVIRON elements and
       the elements of an array created by split() that are  numeric  strings.
       The  basic  idea  is  that  user input, and only user input, that looks
       numeric, should be treated that way.
       Uninitialized variables have the numeric value 0 and the  string  value
       "" (the null, or empty, string).
   Octal and Hexadecimal Constants
       Starting  with version 3.1 of gawk , you may use C-style octal and hex-
       adecimal constants in your AWK program source code.  For  example,  the
       octal  value  011 is equal to decimal 9, and the hexadecimal value 0x11
       is equal to decimal 17.
   String Constants
       String constants in AWK are sequences of  characters  enclosed  between
       double quotes (").  Within strings, certain escape sequences are recog-
       nized, as in C.  These are:
       \\   A literal backslash.
       \a   The “alert” character; usually the ASCII BEL character.
       \b   backspace.
       \f   form-feed.
       \n   newline.
       \r   carriage return.
       \t   horizontal tab.
       \v   vertical tab.
       \xhex digits
            The character represented by the string of hexadecimal digits fol-
            lowing the \x.  As in ANSI C, all following hexadecimal digits are
            considered part of the escape sequence.  (This feature should tell
            us something about language design by committee.)  E.g., "\x1B" is
            the ASCII ESC (escape) character.
       \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 regular expres-
       sions (e.g., /[ \t\f\n\r\v]/ matches whitespace characters).
       In compatibility mode, the characters represented by octal and hexadec-
       imal  escape  sequences  are  treated  literally  when  used in regular
       expression constants.  Thus, /a\52b/ is equivalent to /a\*b/.

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 is executed for every single
       record of input.  A missing action is equivalent to
              { print }
       which prints the entire record.
       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 automatically 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  state-
       ments 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 statement is executed
       for  each  input  record  that matches the regular 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 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, other-
       wise  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 record that matches pat-
       tern1, and continuing until a record that matches pattern2,  inclusive.
       It does not combine 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 including newline.
       ^          matches the beginning of a string.
       $          matches the end of a string.
       [abc...]   character list, matches any of the characters abc....
       [^abc...]  negated character list, matches any character except abc....
       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.
       r{n}
       r{n,}
       r{n,m}     One  or two numbers inside braces denote an interval expres-
                  sion.  If there is one number in the braces,  the  preceding
                  regular  expression r is repeated n times.  If there are two
                  numbers separated by a comma, r is repeated n  to  m  times.
                  If  there  is  one  number  followed  by  a comma, then r is
                  repeated at least n times.
                  Interval expressions are only available if either --posix or
                  --re-interval is specified on the command line.

       \y         matches  the empty string at either the beginning or the end
                  of a word.

       \B         matches the empty string within a word.

       \<         matches the empty string at the beginning of a word.

       \>         matches the empty string at the end of a word.

       \w         matches any word-constituent character  (letter,  digit,  or
                  underscore).

       \W         matches any character that is not word-constituent.

       \         matches  the  empty  string  at  the  beginning  of a buffer
                  (string).

       \         matches the empty string at the end of a buffer.

       The escape sequences that are valid in string constants (see below) are
       also valid in regular expressions.

       Character  classes  are a new feature introduced in the POSIX standard.
       A character class is a special notation for describing lists of charac-
       ters  that  have  a specific attribute, but where the actual characters
       themselves can vary from country to country and/or from  character  set
       to  character  set.   For  example, the notion of what is an alphabetic
       character differs in the USA and in France.

       A character class is only valid in  a  regular  expression  inside  the
       brackets  of a character list.  Character classes consist of [:, a key-
       word denoting the class, and :].  The character classes defined by  the
       POSIX standard are:

       [:alnum:]  Alphanumeric characters.

       [:alpha:]  Alphabetic characters.

       [:blank:]  Space or tab characters.

       [:cntrl:]  Control characters.

       [:digit:]  Numeric characters.

       [:graph:]  Characters that are both printable and visible.  (A space is
                  printable, but not visible, while an a is both.)

       [:lower:]  Lower-case alphabetic characters.

       [:print:]  Printable characters (characters that are not control  char-
                  acters.)

       [:punct:]  Punctuation characters (characters that are not letter, dig-
                  its, control characters, or space characters).

       [:space:]  Space characters (such as space, tab, and formfeed, to  name
                  a few).

       [:upper:]  Upper-case alphabetic characters.

       [:xdigit:] Characters that are hexadecimal digits.

       For  example,  before the POSIX standard, to match alphanumeric charac-
       ters, you would have had to write /[A-Za-z0-9]/.  If your character set
       had  other  alphabetic characters in it, this would not match them, and
       if your character set collated differently from ASCII, this  might  not
       even match the ASCII alphanumeric characters.  With the POSIX character
       classes, you can write /[[:alnum:]]/, and this matches  the  alphabetic
       and numeric characters in your character set.

       Two  additional special sequences can appear in character lists.  These
       apply to non-ASCII  character  sets,  which  can  have  single  symbols
       (called  collating  elements)  that  are represented with more than one
       character, as well as several characters that are equivalent  for  col-
       lating,  or  sorting,  purposes.   (E.g.,  in French, a plain “e” and a
       grave-accented e` are equivalent.)

       Collating Symbols
              A  collating  symbol  is  a  multi-character  collating  element
              enclosed  in [.  and .].  For example, if ch is a collating ele-
              ment, then [[.ch.]]  is a regular expression that  matches  this
              collating  element,  while  [ch]  is  a  regular expression that
              matches either c or h.

       Equivalence Classes
              An equivalence class is a locale-specific name  for  a  list  of
              characters  that are equivalent.  The name is enclosed in [= and
              =].  For example, the name e might be used to represent  all  of
              “e,”  “,”  and “`.”  In this case, [[=e=]] is a regular expres-
              sion that matches any of e, , or `.

       These features are very valuable in non-English speaking locales.   The
       library  functions  that gawk uses for regular expression matching cur-
       rently only recognize POSIX character classes; they  do  not  recognize
       collating symbols or equivalence classes.

       The  \y, \B, \<, \>, \w, \W, \, and \ operators are specific to gawk;
       they are extensions based on facilities in the GNU  regular  expression
       libraries.

       The various command line options control how gawk interprets characters
       in regular expressions.

       No options
              In the default case, gawk provide all the  facilities  of  POSIX
              regular  expressions  and  the  GNU regular expression operators
              described above.  However, interval  expressions  are  not  sup-
              ported.

       --posix
              Only  POSIX regular expressions are supported, the GNU operators
              are not special.  (E.g., \w  matches  a  literal  w).   Interval
              expressions are allowed.

       --traditional
              Traditional  Unix  awk regular expressions are matched.  The GNU
              operators are not special, interval expressions are  not  avail-
              able,  and  neither are the POSIX character classes ([[:alnum:]]
              and so on).   Characters  described  by  octal  and  hexadecimal
              escape  sequences  are treated literally, even if they represent
              regular expression metacharacters.

       --re-interval
              Allow interval  expressions  in  regular  expressions,  even  if
              --traditional has been provided.

   Actions
       Action  statements  are enclosed in braces, { and }.  Action statements
       consist of the usual assignment, conditional,  and  looping  statements
       found  in  most  languages.   The  operators,  control  statements, and
       input/output statements available are patterned after those in C.

   Operators
       The operators in AWK, in order of decreasing precedence, are


       (...)       Grouping

       $           Field reference.

       ++ --       Increment and decrement, both prefix and postfix.

       ^           Exponentiation (** may  also  be  used,  and  **=  for  the
                   assignment operator).

       + - !       Unary plus, unary minus, and logical negation.

       * / %       Multiplication, division, and modulus.

       + -         Addition and subtraction.

       space       String concatenation.

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

       ~ !~        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.

       in          Array membership.

       &&          Logical AND.

       ||          Logical OR.

       ?:          The  C  conditional  expression.  This has the form expr1 ?
                   expr2 : expr3.  If expr1 is true, the value of the  expres-
                   sion  is  expr2,  otherwise it is expr3.  Only one of expr2
                   and expr3 is evaluated.

       = += -=
       *= /= %= ^= Assignment.  Both absolute assignment  (var  =  value)  and
                   operator-assignment (the other forms) are supported.

   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(file [, how])   Close file, pipe or co-process.  The optional how
                             should only be used when closing  one  end  of  a
                             two-way  pipe  to  a  co-process.   It  must be a
                             string value, either "to" or "from".

       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 NR, FNR.

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

       command | getline [var]
                             Run command piping the output either into  $0  or
                             var, as above.

       command |& getline [var]
                             Run  command  as  a  co-process piping the output
                             either into $0 or var,  as  above.   Co-processes
                             are a gawk extension.

       next                  Stop  processing  the  current input record.  The
                             next input record is read and  processing  starts
                             over  with  the first pattern in the AWK program.
                             If the end of the input data is reached, the  END
                             block(s), if any, are executed.

       nextfile              Stop processing the current input file.  The next
                             input record read comes from the next input file.
                             FILENAME  and ARGIND are updated, FNR is reset to
                             1, and processing starts over with the first pat-
                             tern  in the AWK program. If the end of the input
                             data is reached, the END block(s),  if  any,  are
                             executed.

       print                 Prints  the current record.  The output record is
                             terminated with the value of the ORS variable.

       print expr-list       Prints expressions.  Each expression is separated
                             by  the  value  of  the OFS variable.  The output
                             record is terminated 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
                             systems.)

       fflush([file])        Flush any buffers associated with the open output
                             file  or  pipe  file.   If  file is missing, then
                             standard output is flushed.  If file is the  null
                             string, then all open output files and pipes have
                             their buffers flushed.

       Additional output redirections are allowed for print and printf.

       print ... >> file
              appends output to the file.

       print ... | command
              writes on a pipe.

       print ... |& command
              sends data to a co-process.

       The getline command returns 0 on end of file and -1 on an error.   Upon
       an error, ERRNO contains a string describing the problem.

       NOTE: If using a pipe or co-process to getline, or from print or printf
       within a loop, you must use close() to create new instances of the com-
       mand.  AWK does not automatically close pipes or co-processes when they
       return EOF.

   The printf Statement
       The AWK versions of the printf statement and  sprintf()  function  (see
       below) accept the following conversion specification 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, %i  A decimal number (the integer part).

       %e ,  %E
               A floating point number of the form [-]d.dddddde[+-]dd.  The %E
               format uses E instead of e.

       %f      A floating point number of the form [-]ddd.dddddd.

       %g ,  %G
               Use %e or %f conversion, whichever is shorter, with nonsignifi-
               cant zeros suppressed.  The %G format uses %E instead of %e.

       %o      An unsigned octal number (also an integer).

       %u      An unsigned decimal number (again, an integer).

       %s      A character string.

       %x ,  %X
               An unsigned hexadecimal number (an  integer).   The  %X  format
               uses ABCDEF instead of abcdef.

       %%      A single % character; no argument is converted.

       NOTE: When using the integer format-control letters for values that are
       outside the range of a C long integer, gawk switches to the  %g  format
       specifier.  If  --lint is provided on the command line gawk warns about
       this.  Other versions of awk may print invalid values or  do  something
       else entirely.

       Optional,  additional  parameters may lie between the % and the control
       letter:

       count$ Use the count’th argument at this point in the formatting.  This
              is  called  a positional specifier and is intended primarily for
              use in translated versions of format strings, not in the  origi-
              nal text of an AWK program.  It is a gawk extension.

       -      The expression should be left-justified within its field.

       space  For  numeric  conversions,  prefix positive values with a space,
              and negative values with a minus sign.

       +      The plus sign, used before the width modifier (see below),  says
              to  always  supply  a  sign for numeric conversions, even if the
              data to be formatted is positive.  The  +  overrides  the  space
              modifier.

       #      Use  an  “alternate  form” for certain control letters.  For %o,
              supply a leading zero.  For %x, and %X, supply a leading  0x  or
              0X  for a nonzero result.  For %e, %E, and %f, the result always
              contains a decimal point.  For %g, and %G,  trailing  zeros  are
              not removed from the result.

       0      A  leading 0 (zero) acts as a flag, that indicates output should
              be padded with zeroes instead of spaces.  This applies  even  to
              non-numeric  output  formats.  This flag only has an effect when
              the field width is wider than the value to be printed.

       width  The field should be padded to this width.  The field is normally
              padded  with  spaces.  If the 0 flag has been used, it is padded
              with zeroes.

       .prec  A number that specifies the precision to use when printing.  For
              the  %e, %E, and %f formats, this specifies the number of digits
              you want printed to the right of the decimal point.  For the %g,
              and  %G  formats, it specifies the maximum number of significant
              digits.  For the %d, %o, %i, %u, %x, and %X formats,  it  speci-
              fies  the  minimum number of digits to print.  For %s, it speci-
              fies the maximum number  of  characters  from  the  string  that
              should be printed.

       The dynamic width and prec capabilities of the ANSI C printf() routines
       are supported.  A * in place of either the width or prec specifications
       causes  their  values  to  be taken from the argument list to printf or
       sprintf().  To use a positional specifier with a dynamic width or  pre-
       cision,  supply the count$ after the * in the format string.  For exam-
       ple, "%3$*2$.*1$s".

   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).  These file
       names may also be used on the command line to  name  data  files.   The
       filenames are:

       /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"

       The  following  special  filenames  may  be used with the |& co-process
       operator for creating TCP/IP network connections.

       /inet/tcp/lport/rhost/rport  File for TCP/IP connection on  local  port
                                    lport  to remote host rhost on remote port
                                    rport.  Use a port of 0 to have the system
                                    pick a port.

       /inet/udp/lport/rhost/rport  Similar, but use UDP/IP instead of TCP/IP.

       /inet/raw/lport/rhost/rport  Reserved for future use.

       Other special filenames provide access to information about the running
       gawk  process.   These  filenames  are  now obsolete.  Use the PROCINFO
       array to obtain the information they provide.  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 cur-
                   rent process, in decimal, terminated with a newline.

       /dev/pgrpid Reading this file returns the process group ID of the  cur-
                   rent process, in decimal, terminated with a newline.

       /dev/user   Reading this file returns a single record terminated with a
                   newline.  The fields are separated with spaces.  $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.

   Numeric Functions
       AWK has the following built-in arithmetic functions:


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

       cos(expr)     Returns the cosine of expr, which is in radians.

       exp(expr)     The exponential function.

       int(expr)     Truncates to integer.

       log(expr)     The natural logarithm function.

       rand()        Returns a random number N, between 0 and 1, such that 0 ≤
                     N < 1.

       sin(expr)     Returns the sine of expr, which is in radians.

       sqrt(expr)    The square root function.

       srand([expr]) Uses  expr as a new seed for the random number generator.
                     If no expr is provided, the time of  day  is  used.   The
                     return  value  is the previous seed for the random number
                     generator.

   String Functions
       Gawk has the following built-in string functions:


       asort(s [, d])          Returns the number of elements  in  the  source
                               array  s.   The  contents of s are sorted using
                               gawk’s normal rules for comparing  values,  and
                               the  indexes  of  the  sorted  values  of s are
                               replaced with sequential integers starting with
                               1. If the optional destination array d is spec-
                               ified, then s is first duplicated into  d,  and
                               then  d  is  sorted, leaving the indexes of the
                               source array s unchanged.

       asorti(s [, d])         Returns the number of elements  in  the  source
                               array  s.   The behavior is the same as that of
                               asort(), except that the array indices are used
                               for  sorting, not the array values.  When done,
                               the array is indexed numerically, and the  val-
                               ues  are  those  of  the original indices.  The
                               original values are lost; thus provide a second
                               array if you wish to preserve the original.

       gensub(r, s, h [, t])   Search  the  target string t for matches of the
                               regular expression r.  If h is a string  begin-
                               ning with g or G, then replace all matches of r
                               with s.  Otherwise, h is  a  number  indicating
                               which  match of r to replace.  If t is not sup-
                               plied, $0 is used instead.  Within the replace-
                               ment  text  s,  the  sequence  \n, where n is a
                               digit from 1 to 9, may be used to indicate just
                               the  text  that  matched the n’th parenthesized
                               subexpression.  The sequence \0 represents  the
                               entire  matched  text, as does the character &.
                               Unlike sub() and gsub(), the modified string is
                               returned as the result of the function, and the
                               original target string is not changed.

       gsub(r, s [, t])        For each substring matching the regular expres-
                               sion  r  in the string t, substitute the string
                               s, and return the number of substitutions.   If
                               t  is  not  supplied,  use  $0.   An  &  in the
                               replacement text is replaced with the text that
                               was  actually matched.  Use \& to get a literal
                               &.  (This must be typed  as  "\\&";  see  GAWK:
                               Effective  AWK Programming for a fuller discus-
                               sion of the rules for &s  and  backslashes  in
                               the replacement text of sub(), gsub(), and gen-
                               sub().)

       index(s, t)             Returns the index of the string t in the string
                               s,  or  0  if  t is not present.  (This implies
                               that character indices start at one.)

       length([s])             Returns the length of  the  string  s,  or  the
                               length of $0 if s is not supplied.

       match(s, r [, a])       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.
                               Note that the argument order is the same as for
                               the  ~  operator: str ~ re.  If array a is pro-
                               vided, a is cleared and then elements 1 through
                               n  are filled with the portions of s that match
                               the corresponding  parenthesized  subexpression
                               in  r.  The 0’th element of a contains the por-
                               tion of s matched by the entire regular expres-
                               sion  r.   Subscripts  a[n,  "start"], and a[n,
                               "length"] provide the  starting  index  in  the
                               string  and length respectively, of each match-
                               ing substring.

       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.   Splitting
                               behaves   identically   to   field   splitting,
                               described above.

       sprintf(fmt, expr-list) Prints  expr-list according to fmt, and returns
                               the resulting string.

       strtonum(str)           Examines str, and returns  its  numeric  value.
                               If  str  begins  with  a  leading 0, strtonum()
                               assumes that str is an octal  number.   If  str
                               begins  with  a  leading  0x  or 0X, strtonum()
                               assumes that str is a hexadecimal number.

       sub(r, s [, t])         Just like gsub(), but only the  first  matching
                               substring is replaced.

       substr(s, i [, n])      Returns  the at most n-character substring of s
                               starting at i.  If n is omitted, 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  corresponding  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  corresponding  upper-case  counterparts.
                               Non-alphabetic characters are left unchanged.

   Time Functions
       Since  one  of the primary uses of AWK programs is processing log files
       that contain time stamp information, gawk provides the following  func-
       tions for obtaining time stamps and formatting them.


       mktime(datespec)
                 Turns datespec into a time stamp of the same form as returned
                 by systime().  The datespec is a string of the form  YYYY  MM
                 DD  HH  MM  SS[  DST].  The contents of the string are six or
                 seven numbers representing respectively the full year includ-
                 ing  century,  the  month  from 1 to 12, the day of the month
                 from 1 to 31, the hour of the day from 0 to  23,  the  minute
                 from  0  to  59, and the second from 0 to 60, and an optional
                 daylight saving flag.  The values of these numbers  need  not
                 be  within  the  ranges specified; for example, an hour of -1
                 means 1 hour before midnight.  The origin-zero Gregorian cal-
                 endar  is  assumed,  with year 0 preceding year 1 and year -1
                 preceding year 0.  The time is assumed to  be  in  the  local
                 timezone.   If the daylight saving flag is positive, the time
                 is assumed to be daylight saving time; if zero, the  time  is
                 assumed  to  be standard time; and if negative (the default),
                 mktime() attempts to determine whether daylight  saving  time
                 is  in  effect  for the specified time.  If datespec does not
                 contain enough elements or if the resulting time  is  out  of
                 range, mktime() returns -1.

       strftime([format [, timestamp]])
                 Formats  timestamp  according to the specification in format.
                 The timestamp should be of the same form as returned by  sys-
                 time().   If timestamp is missing, the current time of day is
                 used.  If format is missing, a default format  equivalent  to
                 the output of date(1) is used.  See the specification for the
                 strftime() function in ANSI C for the format conversions that
                 are  guaranteed  to be available.  A public-domain version of
                 strftime(3) and a man page for it come  with  gawk;  if  that
                 version  was  used to build gawk, then all of the conversions
                 described in that man page are available to gawk.

       systime() Returns the current time of day  as  the  number  of  seconds
                 since the Epoch (1970-01-01 00:00:00 UTC on POSIX systems).

   Bit Manipulations Functions
       Starting with version 3.1 of gawk, the following bit manipulation func-
       tions are available.  They work by converting double-precision floating
       point  values  to unsigned long integers, doing the operation, and then
       converting the result back to floating point.  The functions are:

       and(v1, v2)         Return the bitwise AND of the values provided by v1
                           and v2.

       compl(val)          Return the bitwise complement of val.

       lshift(val, count)  Return  the  value  of  val,  shifted left by count
                           bits.

       or(v1, v2)          Return the bitwise OR of the values provided by  v1
                           and v2.

       rshift(val, count)  Return  the  value  of  val, shifted right by count
                           bits.

       xor(v1, v2)         Return the bitwise XOR of the values provided by v1
                           and v2.


   Internationalization Functions
       Starting  with version 3.1 of gawk, the following functions may be used
       from within your AWK program for translating strings at run-time.   For
       full details, see GAWK: Effective AWK Programming.

       bindtextdomain(directory [, domain])
              Specifies  the  directory where gawk looks for the .mo files, in
              case they will not or cannot be placed in the ‘‘standard’’ loca-
              tions  (e.g.,  during  testing).  It returns the directory where
              domain is ‘‘bound.’’
              The default domain is the value of TEXTDOMAIN.  If directory  is
              the  null string (""), then bindtextdomain() returns the current
              binding for the given domain.

       dcgettext(string [, domain [, category]])
              Returns the translation of string  in  text  domain  domain  for
              locale  category  category.  The default value for domain is the
              current value of TEXTDOMAIN.  The default value for category  is
              "LC_MESSAGES".
              If you supply a value for category, it must be a string equal to
              one of the known locale categories described in GAWK:  Effective
              AWK  Programming.   You  must  also  supply  a text domain.  Use
              TEXTDOMAIN if you want to use the current domain.

       dcngettext(string1 , string2 , number [, domain [, category]])
              Returns the plural form used for number of  the  translation  of
              string1  and  string2  in text domain domain for locale category
              category.  The default value for domain is the current value  of
              TEXTDOMAIN.  The default value for category is "LC_MESSAGES".
              If you supply a value for category, it must be a string equal to
              one of the known locale categories described in GAWK:  Effective
              AWK  Programming.   You  must  also  supply  a text domain.  Use
              TEXTDOMAIN if you want to use the current domain.


USER-DEFINED FUNCTIONS

       Functions in AWK are defined as follows:

              function name(parameter list) { statements }

       Functions are executed when they are called from within expressions  in
       either patterns or actions.  Actual parameters 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  pro-
       vision 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 and b are local
              {
                   ...
              }

              /abc/     { ... ; f(1, 2) ; ... }

       The left parenthesis in a function call is required to immediately fol-
       low the function name, without any intervening 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.  Function parame-
       ters used as local variables are initialized to the null string and the
       number zero upon function invocation.

       Use return expr to return a value from a function.  The return value is
       undefined if no value is  provided,  or  if  the  function  returns  by
       “falling off” the end.

       If  --lint has been provided, gawk warns about calls to undefined func-
       tions at parse time, instead of at  run  time.   Calling  an  undefined
       function at run time is a fatal error.

       The word func may be used in place of function.


DYNAMICALLY LOADING NEW FUNCTIONS

       Beginning  with version 3.1 of gawk, you can dynamically add new built-
       in functions to the running gawk interpreter.   The  full  details  are
       beyond  the scope of this manual page; see GAWK: Effective AWK Program-
       ming for the details.


       extension(object, function)
               Dynamically link the shared object file named  by  object,  and
               invoke  function  in  that  object,  to perform initialization.
               These should both be provided as strings.   Returns  the  value
               returned by function.

       This  function  is  provided and documented in GAWK: Effective AWK Pro-
       gramming, but everything about this feature is likely to change in  the
       next  release.   We STRONGLY recommend that you do not use this feature
       for anything that you arent willing to redo.


SIGNALS

       pgawk accepts two signals.  SIGUSR1 causes it to  dump  a  profile  and
       function  call  stack to the profile file, which is either awkprof.out,
       or whatever file was named with the --profile option.  It then  contin-
       ues  to  run.   SIGHUP  causes it to dump the profile and function call
       stack and then exit.


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 }
       Run an external command for particular lines of data:

            tail -f access_log |
            awk /myhome.html/ { system("nmap " $1 ">> logdir/myhome.html") }


INTERNATIONALIZATION

       String constants are sequences of characters enclosed in double quotes.
       In non-English speaking environments, it is possible to mark strings in
       the AWK program as requiring translation to  the  native  natural  lan-
       guage. Such strings are marked in the AWK program with a leading under-
       score (“_”).  For example,

              gawk BEGIN { print "hello, world" }

       always prints hello, world.  But,

              gawk BEGIN { print _"hello, world" }

       might print bonjour, monde in France.

       There are several steps involved in producing and running a localizable
       AWK program.

       1.  Add  a BEGIN action to assign a value to the TEXTDOMAIN variable to
           set the text domain to a name associated with your program.

                BEGIN { TEXTDOMAIN = "myprog" }

           This allows gawk to find the .mo file associated with your program.
           Without this step, gawk uses the messages text domain, which likely
           does not contain translations for your program.

       2.  Mark all strings that should  be  translated  with  leading  under-
           scores.

       3.  If necessary, use the dcgettext() and/or bindtextdomain() functions
           in your program, as appropriate.

       4.  Run gawk --gen-po -f myprog.awk > myprog.po to generate a .po  file
           for your program.

       5.  Provide  appropriate  translations,  and build and install a corre-
           sponding .mo file.

       The internationalization features are described in full detail in GAWK:
       Effective AWK Programming.


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  incor-
       porates  the following user visible features which are not described in
       the AWK book, but are part of the Bell Laboratories version of awk, and
       are in the POSIX standard.

       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,  the
       -v option for assigning variables before program execution was added to
       accommodate applications that depended upon the  old  behavior.   (This
       feature  was  agreed  upon  by  both  the Bell Laboratories and the 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 warns about but other-
       wise  ignores  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  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 the Bell Laboratories version); the tolower()
       and toupper() built-in functions (from the Bell Laboratories  version);
       and  the  ANSI C conversion specifications in printf (done first in the
       Bell Laboratories version).


HISTORICAL FEATURES

       There are two features of historical AWK implementations that gawk sup-
       ports.   First,  it  is possible to call the length() built-in function
       not only with no argument, but even without parentheses!  Thus,

              a = length     # Holy Algol 60, Batman!

       is the same as either of

              a = length()
              a = length($0)

       This feature is marked as “deprecated” in the POSIX standard, and  gawk
       issues  a  warning  about its use if --lint is specified on the command
       line.

       The other feature is the use of either the continue or the break state-
       ments  outside  the  body of a while, for, or do loop.  Traditional AWK
       implementations have treated such  usage  as  equivalent  to  the  next
       statement.   Gawk  supports this usage if --traditional has been speci-
       fied.


GNU EXTENSIONS

       Gawk has a number of extensions to POSIX awk.  They  are  described  in
       this  section.   All  the  extensions described here can be disabled by
       invoking gawk with the --traditional option.

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

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

       · The \x escape sequence.  (Disabled with --posix.)

       · The fflush() function.  (Disabled with --posix.)

       · The  ability  to  continue  lines  after  ?   and  :.  (Disabled with
         --posix.)

       · Octal and hexadecimal constants in AWK programs.

       · The ARGIND, BINMODE, ERRNO, LINT, RT and TEXTDOMAIN variables are not
         special.

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

       · The FIELDWIDTHS variable and fixed-width field splitting.

       · The PROCINFO array is not available.

       · The use of RS as a regular expression.

       · The  special  file names available for I/O redirection are not recog-
         nized.

       · The |& operator for creating co-processes.

       · The ability to split out individual characters using the null  string
         as the value of FS, and as the third argument to split().

       · The optional second argument to the close() function.

       · The optional third argument to the match() function.

       · The ability to use positional specifiers with printf and sprintf().

       · The use of delete array to delete the entire contents of an array.

       · The  use of nextfile to abandon processing of the current input file.

       · The and(), asort(), asorti(), bindtextdomain(), compl(), dcgettext(),
         dcngettext(),   gensub(),   lshift(),   mktime(),   or(),   rshift(),
         strftime(), strtonum(), systime() and xor() functions.

       · Localizable strings.

       · Adding new built-in functions dynamically with the extension()  func-
         tion.

       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 an output file or pipe, respectively.  It returns the process’s
       exit status when closing an input pipe.  The return value is -1 if  the
       named file, pipe or co-process was not opened with a redirection.

       When  gawk is invoked with the --traditional option, if the fs argument
       to the -F option is “t”, then FS is set to  the  tab  character.   Note
       that  typing  gawk -F\t ...  simply causes the shell to quote the “t,”,
       and does not pass “\t” to the -F option.  Since this is a  rather  ugly
       special  case, it is not the default behavior.  This behavior also does
       not occur if --posix has been specified.  To really get a tab character
       as  the  field  separator, it is best to use single quotes: gawk -F\t
       ....

       If gawk is configured with the --enable-switch option to the  configure
       command, then it accepts an additional control-flow statement:
              switch (expression) {
              case value|regex : statement
              ...
              [ default: statement ]
              }


ENVIRONMENT VARIABLES

       The  AWKPATH  environment  variable  can  be  used to provide a list of
       directories that gawk searches when looking for files named via the  -f
       and --file options.

       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 issues a warning message to this effect.


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.

       GAWK:  Effective  AWK  Programming,  Edition 3.0, published by the Free
       Software Foundation, 2001.


BUGS

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

       Syntactically  invalid  single  character programs tend to overflow the
       parse stack, generating a rather unhelpful message.  Such programs  are
       surprisingly  difficult to diagnose in the completely general case, and
       the effort to do so really is not worth it.


AUTHORS

       The original version of UNIX awk was designed and implemented by Alfred
       Aho, Peter Weinberger, and Brian Kernighan of Bell Laboratories.  Brian
       Kernighan continues to maintain and enhance it.

       Paul Rubin and Jay Fenlason, of the  Free  Software  Foundation,  wrote
       gawk,  to be compatible with the original version of awk distributed in
       Seventh Edition UNIX.  John Woods contributed a number  of  bug  fixes.
       David  Trueman,  with contributions from Arnold Robbins, made gawk com-
       patible with the new version of UNIX awk.  Arnold Robbins is  the  cur-
       rent 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  Dar-
       rel  Hankerson.   Fred  Fish  supplied  support  for the Amiga, Stephen
       Davies provided the Tandem port, and Martin  Brown  provided  the  BeOS
       port.


VERSION INFORMATION

       This man page documents gawk, version 3.1.4.


BUG REPORTS

       If  you  find  a  bug  in  gawk,  please  send  electronic mail to bug-
       gawk@gnu.org.  Please include your operating system and  its  revision,
       the  version of gawk (from gawk --version), 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 yours 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 language.

       Whatever you do, do NOT post a bug report in comp.lang.awk.  While  the
       gawk  developers  occasionally read this newsgroup, posting bug reports
       there is an unreliable way to report bugs.   Instead,  please  use  the
       electronic mail addresses given above.

       If you’re using a GNU/Linux system or BSD-based system, you may wish to
       submit a bug report to the vendor of your distribution.   That’s  fine,
       but  please  send  a  copy to the official email address as well, since
       there’s no guarantee that the bug will be forwarded to the  gawk  main-
       tainer.


ACKNOWLEDGEMENTS

       Brian  Kernighan of Bell Laboratories provided valuable assistance dur-
       ing testing and debugging.  We thank him.


COPYING PERMISSIONS

       Copyright © 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
       2001, 2002, 2003, 2004 Free Software Foundation, Inc.

       Permission  is  granted  to make and distribute verbatim copies of this
       manual page provided the copyright notice and  this  permission  notice
       are preserved on all copies.

       Permission  is granted to copy and distribute modified versions of this
       manual page under the conditions for verbatim  copying,  provided  that
       the  entire  resulting derived work is distributed under the terms of a
       permission notice identical to this one.

       Permission is granted to copy and distribute translations of this  man-
       ual page into another language, under the above conditions for modified
       versions, except that this permission notice may be stated in a  trans-
       lation approved by the Foundation.



Free Software Foundation         July 28 2004                          GAWK(1)

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