path: root/doc/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 found in the System V  Re-
       lease 4 version of UNIX awk.  Gawk also provides more recent Bell Labs awk extensions, and
       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.

OPTION FORMAT
       Gawk options may be either the traditional POSIX one letter options, or the GNU style long
       options.  POSIX options start with a single "-", while long options start with "--".  Long
       options are provided for both GNU-specific 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 op-
       tion, as detailed below.  Arguments 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 abbreviation remains unique.

OPTIONS
       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 Bell Labs research version of UNIX awk.  They  are  ignored  by
              gawk, since gawk has no pre-defined limits.

       -W traditional
       -W compat
       --traditional
       --compat
              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 exits successfully.

       -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
       --lint Provide warnings about constructs that are dubious or non-portable to other AWK im-
              plementations.

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

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

              +o \x escape sequences are not recognized.

              +o Only space and tab act as field separators when FS is set to a single space, new-
                line does not.

              +o The synonym func for the keyword function is not recognized.

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

              +o The fflush() function is not available.

       -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 intermix-
              ing of library functions (used via the -f and --file options) with source code  en-
              tered  on  the command line.  It is intended primarily for medium to large AWK pro-
              grams 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 Standards, these op-
              tions 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 argu-
              ment 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  --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 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/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 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
       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 pattern in the AWK pro-
       gram.  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  val-
       ues  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  simu-
       lated.   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 in-
       put  that  matches this regular expression will separate the record.  However, in compati-
       bility mode, only the first character of its string value is used for separating  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 newline character always acts as a field separator,  in  addi-
       tion to whatever 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 sepa-
       rate field.  Otherwise, 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 that the value of  IGNORECASE
       (see below) will also affect 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 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 record may be referenced by its position, $1, $2, and so on.  $0
       is the whole record.  The value of a field may be assigned to as well.  Fields need not be
       referenced by constants:

              n = 5
              print $n

       prints the fifth field in the input 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.   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.  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.

   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.

       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 /home/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;
                   the semantics may 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 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 match-
                   ing  in rules, field splitting with FS, record separating with RS, regular ex-
                   pression matching with ~ and !~, and the gensub(), gsub(),  index(),  match(),
                   split(), and sub() pre-defined functions will all ignore case when doing regu-
                   lar 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 vari-
                   ables, 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 character set is used when ignoring case.  NOTE: In versions of
                   gawk prior to 3.0, IGNORECASE only affected regular expression operations.  It
                   now affects string comparisons as well.

       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.

       RS          The input record separator, by default a newline.

       RT          The record terminator.  Gawk sets RT to the input text that matched the  char-
                   acter or regular expression specified by RS.

       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, 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 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 con-
       verted  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.

       Note that string constants, such as "57", are not numeric strings, they  are  string  con-
       stants.   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 nu-
       meric, should be treated that way.

       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 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, 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.  Simi-
       larly, 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  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
       pattern  used  for  testing is the second pattern, otherwise it is the third.  Only one of
       the second and third patterns is evaluated.

       The pattern1, pattern2 form of an expression is called a range pattern.   It  matches  all
       input  records starting with a record 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 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 expression.   If  there  is
                  one number in the braces, the preceding regexp 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 legal in reg-
       ular expressions.

       Character  classes  are a new feature introduced in the POSIX standard.  A character class
       is a special notation for describing lists of characters 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  charac-
       ter differs in the USA and in France.

       A  character  class  is  only  valid  in a regexp inside the brackets of a character list.
       Character classes consist of [:, a keyword denoting the class, and :].  Here are the char-
       acter classes defined by the POSIX standard.

       [: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 characters.)

       [:punct:]
              Punctuation characters (characters that are not letter, digits, 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 characters, 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.  With the POSIX character classes, you can write /[[:alnum:]]/,
       and this will match all 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 repre-
       sented with more than one character, as well as several characters that are equivalent for
       collating,  or  sorting,  purposes.  (E.g., in French, a plain "e" and a grave-accented e`
       are equivalent.)

       Collating Symbols
              A collating symbols is a multi-character collating element enclosed in [.  and  .].
              For  example, if ch is a collating element, then [[.ch.]]  is a regexp that matches
              this collating element, while [ch] is a regexp 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," "e`," and "e`."  In this case,  [[=e]]  is  a  regexp
              that matches any of
               .BR e ,
               .BR e' , or
               .BR e` .

       These  features  are very valuable in non-English speaking locales.  The library functions
       that gawk uses for regular expression matching currently 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 regexp libraries.

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

       No options
              In the default case, gawk provide all the facilities of POSIX regexps and  the  GNU
              regexp operators described above.  However, interval expressions are not supported.

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

       --traditional
              Traditional Unix awk regexps are matched.  The GNU operators are not  special,  in-
              terval  expressions  are not available, and neither are the POSIX character classes
              ([[:alnum:]] and so on).  Characters described by octal and hexadecimal escape  se-
              quences are treated literally, even if they represent regexp metacharacters.

       --re-interval
              Allow interval expressions in regexps, 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 expression 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)           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 NR, 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.

       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 pattern
                             in  the  AWK  program.  If the end of the input data is reached, the
                             END block(s), if any, are executed.  NOTE: Earlier versions of  gawk
                             used next file, as two words.  While this usage is still recognized,
                             it generates a warning message and will eventually be removed.

       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.

       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.

       NOTE: If using a pipe to getline, or from print or printf within  a  loop,  you  must  use
       close()  to  create  new instances of the command.  AWK does not automatically close pipes
       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 in-
              stead of e.

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

       %g
       %G     Use %e or %f conversion, whichever  is  shorter,  with  nonsignificant  zeros  sup-
              pressed.  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.

       There are optional, additional parameters that may lie between the % and the control  let-
       ter:

       -      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 will always contain 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 ze-
              roes 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 spa-
              ces.  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 sig-
              nificant digits.  For the %d, %o, %i, %u, %x, and %X formats, it specifies the min-
              imum number of digits to print.  For a string, it specifies 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 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 to 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  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  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 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 between 0 and 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 pro-
                     vided, the time of day will be used.  The return value is the previous  seed
                     for the random number generator.

   String Functions
       Gawk has the following pre-defined string functions:

       gensub(r, s, h [, t])   search  the  target string t for matches of the regular expression
                               r.  If h is a string beginning 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 no t is supplied, $0 is  used  instead.
                               Within the replacement 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 expression r in the string
                               t,  substitute  the  string  s, and return the number of substitu-
                               tions.  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 &.  See Effective AWK Programming  for  a  fuller
                               discussion of the rules for &'s and backslashes in the replacement
                               text of sub(), gsub(), and gensub().

       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.  Splitting  behaves  identi-
                               cally to field splitting, described above.

       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 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  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.  If format is missing, a default format equiva-
                 lent to the output of date(1) will be used.  See the specification for the strf-
                 time()  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.

   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   newline.

       \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).

       In compatibility mode, the characters represented by  octal  and  hexadecimal  escape  se-
       quences  are treated literally when used in regexp constants.  Thus, /a\52b/ is equivalent
       to /a\*b/.

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 for-
       mal parameters declared in the function.  Arrays are passed by reference, other  variables
       are passed by value.

       Since  functions  were  not  originally  part of the AWK language, the provision for local
       variables is rather clumsy: They are declared as extra parameters in the  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.

       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 will warn about calls to undefined functions 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.

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.

       Effective AWK Programming, Edition 1.0, published by the Free Software Foundation, 1995.

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 the Bell  Labs  version  of
       awk, 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 accommo-
       date  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 POSIX standard has it re-
       turn 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 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 op-
       tion.

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

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

              +o The fflush() function.  (Disabled with --posix.)

              +o The systime(), strftime(), and gensub() functions.

              +o The special file names available for I/O redirection are not recognized.

              +o The ARGIND, ERRNO, and RT 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 The use of RS as a regular expression.

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

              +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 nextfile 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 --traditional option, if the fs argument to the -F option is
       "t", then FS will be 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 sepa-
       rator, it is best to use quotes: gawk -F'\t' ....

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     # 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 will issue a  warn-
       ing about its use if --lint is specified on the command line.

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

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

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

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.

       Syntactically invalid single character programs tend to overflow the parse stack, generat-
       ing  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.

VERSION INFORMATION
       This man page documents gawk, version 3.0.5.

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.  Arnold Robbins is the current main-
       tainer.

       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.  Fred Fish supplied support for the Amiga.

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

       Before sending a bug report, please do two things.  First, verify that you have the latest
       version  of gawk.  Many bugs (usually subtle ones) are fixed at each release, and if 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 oc-
       casionally  read  this newsgroup, posting bug reports there is an unreliable way to report
       bugs.  Instead, please use the electronic mail addresses given above.

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

COPYING PERMISSIONS
       Copyright (C) 1996-2000 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 manual page into another
       language,  under  the  above conditions for modified versions, except that this permission
       notice may be stated in a translation approved by the Foundation.

Free Software Foundation                   May 17 2000                                    GAWK(1)