path: root/gawk.1

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 ...

DESCRIPTION
       Gawk  is the GNU Project's implementation of the AWK programming language.  It conforms to
       the definition of the language in the POSIX 1003.2 Command Language  And  Utilities  Stan-
       dard.   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 letter options, or the GNU style long
       options.  POSIX style options start with a single ``-'', while GNU long options start with
       ``--''.   GNU style long options are provided for both GNU-specific features and for POSIX
       mandated features.  Other implementations of the AWK language are likely  to  only  accept
       the traditional one letter options.

       Following  the  POSIX standard, gawk-specific options are supplied via arguments to the -W
       option.  Multiple -W options may be supplied, or multiple arguments may  be  supplied  to-
       gether  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 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 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 recognized.  See GNU EXTEN-
                   SIONS, 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 available options on the error output.
                   Per the GNU Coding Standards, these options  cause  an  immediate,  successful
                   exit.

       -W lint
       --lint      Provide  warnings  about  constructs that are dubious or non-portable to other
                   AWK implementations.
       -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  in-
                   termixing  of  library  functions  (used  via  the -f and --file options) with
                   source code entered on the command line.  It is intended primarily for  medium
                   to large size AWK programs used in shell scripts.
                   The  -W source= form of this option uses the rest of the command line argument
                   for program-text; no other options to -W will be recognized in the same  argu-
                   ment.

       -W version
       --version   Print  version  information for this particular copy of gawk on the error out-
                   put.  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.  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 convention used by most other POSIX programs.

       In  compatibility  mode,  any  other options are flagged as illegal, but are otherwise ig-
       nored.  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 pro-
       gram 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 in-
       clude 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 speci-
       fied  via  the  -v option are performed.  Next, gawk compiles 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 assign-
       ment.  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 sin-
       gle 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 pro-
       gram.  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 separated by
       that character.  Otherwise, FS is expected to be a full regular expression.  In  the  spe-
       cial  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 ex-
       pected to have fixed width, and gawk will split up the record using the specified  widths.
       The value of FS is ignored.  Assigning a new value to FS overrides the use of FIELDWIDTHS,
       and restores the default behavior.

       Each field in the input line may be referenced by its 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 ref-
       erenced 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. How-
       ever, assigning to a non-existent field (e.g., $(NF+2) = 5) will increase the value of NF,
       create  any intervening fields with the null string as their value, and cause the value of
       $0 to be recomputed, with the fields being separated by the value of OFS.   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.  Dy-
                   namically 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 in-
                   dexed by the environment variables, each element being the value of that vari-
                   able (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 system() function.  (This may change in a future version of gawk.)

       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.

       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 IGNORE-
                   CASE  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 initial value of IGNORECASE is zero, so all regular expres-
                   sion 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 newline.

       RS          The  input  record separator, by default a newline.  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 separated by blank lines.  When RS is set to the
                   null  string,  then the newline character always acts as a field separator, in
                   addition to whatever value FS may have.

       RSTART      The index of the first character matched by match(); 0 if no match.

       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  de-
                   fault "\034".

   Arrays
       Arrays  are  subscripted with an expression between square brackets ([ and ]).  If the ex-
       pression is an expression list (expr, expr ...)  then the array subscript is a string con-
       sisting  of  the  concatenation of the (string) value of each expression, separated by the
       value of the SUBSEP variable.  This facility is used to simulate multiply dimensioned  ar-
       rays. For example:

              i = "A" ; j = "B" ; k = "C"
              x[i, j, k] = "hello, world\n"

       assigns  the string "hello, world\n" to the element of the array x which is indexed by the
       string "A\034B\034C". All arrays in AWK are associative, i.e. indexed by string values.

       The special operator in may be used in an if or while 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 ar-
       ray.

       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 interpreted depends upon its context. If used in a numeric expression, it
       will be treated as a number, if used as a string it will be treated as a string.

       To force a variable to be treated as a number, add 0 to it; to force it to be treated as a
       string, concatenate it with the null string.

       When a string must be converted to a number, the conversion is accomplished using 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 variable as the argument.  However, even  though
       all  numbers  in AWK are floating-point, integral values are always converted 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  nu-
       merically.   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.  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 exe-
       cuted for every single line of input.  A missing action is equivalent to

              { print }

       which prints the entire line.

       Comments begin with the ``#'' character, and continue until the end of  the  line.   Blank
       lines may be used to separate statements.  Normally, a statement ends with a newline, how-
       ever, this is not the case for lines ending in a ``,'', ``{'', ``?'',  ``:'',  ``&&'',  or
       ``||''.   Lines ending in do or else also have their statements automatically continued on
       the following line.  In other cases, a line can be 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  writ-
       ten in a single BEGIN block. They are executed before any of the input is read. Similarly,
       all the END blocks are merged, and executed when all the input is exhausted  (or  when  an
       exit  statement  is  executed).  BEGIN and END patterns cannot be combined with other pat-
       terns in pattern expressions.  BEGIN and END patterns cannot have missing action parts.

       For /regular expression/ patterns, the associated statement is  executed  for  each  input
       line  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  ac-
       tions.  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 pat-
       tern  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 combine with any other sort of  pattern  ex-
       pression.

   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 reg-
       ular expressions.

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

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

       = += -=
       *= /= %= ^= Assignment.  Both  absolute  assignment  (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, otherwise 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 postfix.

       $           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
                             program.  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
                             program.  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 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.)

       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 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     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 let-
       ter:

       -      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 ap-
              plies even to the non-numeric output formats.

       .prec  A number indicating the maximum width of strings or digits to the right of the dec-
              imal 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  file-
       names are:

       /dev/pid    Reading  this  file returns the process ID of the current process, in decimal,
                   terminated with a newline.

       /dev/ppid   Reading this file returns the parent process ID of  the  current  process,  in
                   decimal, terminated with a newline.

       /dev/pgrpid Reading this file returns the process group ID of the current process, in dec-
                   imal, terminated with a newline.

       /dev/user   Reading this file returns a single record  terminated  with  a  newline.   The
                   fields  are  separated  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  get-
                   groups(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 pro-
                   vided, 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  in-
                               stead.  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  re-
                               placed.

       substr(s, i, n)         returns  the  n-character  substring  of s starting at i.  If n is
                               omitted, the rest of s is used.

       tolower(str)            returns a copy of the string str, with all the upper-case  charac-
                               ters  in str translated to their corresponding lower-case counter-
                               parts.  Non-alphabetic characters are left unchanged.

       toupper(str)            returns a copy of the string str, with all the lower-case  charac-
                               ters  in str translated to their corresponding upper-case counter-
                               parts.  Non-alphabetic characters are left unchanged.

   Time Functions
       Since one of the primary uses of AWK programs is processing log files  that  contain  time
       stamp information, 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  (Mid-
                 night 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() func-
                 tion 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 are shipped with
                 gawk; if that version was used to build gawk, then all of  the  conversions  de-
                 scribed in that man page are available to gawk.

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

       \\   A literal backslash.

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

       \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 hexadecimal digits following the  \x.   As
            in  ANSI  C,  all  following hexadecimal digits are considered part of the escape se-
            quence.  (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  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 parameters supplied in the function call are used  to  instantiate  the
       formal  parameters  declared in the function.  Arrays are passed by reference, other vari-
       ables are passed by value.

       Since functions were not originally part of the AWK  language,  the  provision  for  local
       variables  is  rather clumsy: They are declared as extra parameters in the 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 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  parameters  used  as  local
       variables are initialized to the null string and the number zero upon function invocation.

       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,  Ad-
       dison-Wesley, 1988. ISBN 0-201-07981-X.

       The GAWK Manual, Edition 0.15, published by the Free Software Foundation, 1993.

POSIX COMPATIBILITY
       A primary goal for gawk is compatibility with the POSIX standard, as well as with the lat-
       est version of UNIX awk.  To this end, gawk incorporates the following user  visible  fea-
       tures  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 execution 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  im-
       plementations,  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  ``fea-
       ture.''   When awk was changed to match its documentation, this option was added to accom-
       modate 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 argu-
       ments.  In compatibility mode, it will warn about, but  otherwise  ignore,  undefined  op-
       tions.   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 specifi-
       cations 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 ex-
       tensions 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 redirection 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 contents of an array.

       The AWK book does not define the return value of the close() function.  Gawk's close() re-
       turns 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  with-
       out 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 the continue statement 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 support this usage if -W posix has not 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 warn-
       ing message to this effect.

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

       If  your  system actually has support for /dev/fd and the associated /dev/stdin, /dev/std-
       out, 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 different 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 recognized.  This fact will not even be  documented  in  the  manual
       page for version 2.16.

AUTHORS
       The  original  version of UNIX awk was designed and implemented by Alfred Aho, Peter Wein-
       berger, 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 Foundation, wrote gawk, to be compatible
       with the original version of awk distributed in Seventh Edition UNIX.  John Woods contrib-
       uted  a  number of bug fixes.  David Trueman, with contributions from Arnold Robbins, made
       gawk compatible with the new version of UNIX awk.

       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.

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

Free Software Foundation                   Apr 18 1994                                    GAWK(1)