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awk command help

       gawk - pattern scanning and processing language


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


       Gawk  is  the GNU Project's implementation of the AWK pro­
       gramming language.  It conforms to the definition  of  the
       language  in  the POSIX 1003.2 Command Language And Utili­
       ties Standard.  This version  in  turn  is  based  on  the
       description  in  The  AWK  Programming  Language,  by Aho,
       Kernighan, and Weinberger, with  the  additional  features
       found in the System V Release 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.


       Gawk options may be either the traditional POSIX one  let­
       ter 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 option, 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.


       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
       -f program-file
       --file program-file
              Read  the AWK program source from the file program-
              file, instead of from the first command line  argu­
              ment.  Multiple -f (or --file) options may be used.
       -mf NNN
       -mr NNN
              Set various memory limits to the value NNN.  The  f
              flag  sets  the maximum number of fields, and the r
              flag sets the maximum record size.  These two flags
              and  the  -m option are from the Bell Labs research
              version of UNIX awk.  They  are  ignored  by  gawk,
              since gawk has no pre-defined limits.
       -W traditional
       -W 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
       -W copyleft
       -W copyright
              Print the short version of the GNU copyright infor­
              mation  message  on  the standard output, and exits
       -W help
       -W usage
              Print a relatively short summary of  the  available
              options  on the standard output.  (Per the GNU Cod­
              ing 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 lint-old
              Provide warnings  about  constructs  that  are  not
              portable to the original version of Unix awk.
              This  turns on compatibility mode, with the follow­
              ing additional restrictions:
              · \x escape sequences are not recognized.
              · Only space and tab act as field  separators  when
                FS is set to a single space, newline does not.
              · The  synonym func for the keyword function is not
              · The operators ** and **= cannot be used in  place
                of ^ and ^=.
              · The fflush() function is not available.
       -W re-interval
              Enable  the  use of interval expressions in regular
              expression  matching  (see   Regular   Expressions,
              below).   Interval  expressions were not tradition­
              ally available in the AWK language. The POSIX stan­
              dard  added  them, to make awk and egrep consistent
              with each other.  However, their use is  likely  to
              break  old AWK programs, so gawk only provides them
              if they are requested with  this  option,  or  when
              --posix is specified.
       -W source program-text
       --source program-text
              Use  program-text as AWK program source code.  This
              option allows the easy intermixing of library func­
              tions  (used  via  the  -f and --file options) with
              source code entered on the  command  line.   It  is
              intended primarily for medium to large AWK programs
              used in shell scripts.
       -W version
              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 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
       In  compatibility  mode,  any other options are flagged as
       illegal, but are otherwise ignored.  In normal  operation,
       as long as program text has been supplied, unknown options
       are passed on to the AWK program in  the  ARGV  array  for
       processing.   This  is particularly useful for running AWK
       programs via the ``#!'' executable interpreter  mechanism.


       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 program text as  if  all
       the  program-files  and command line source texts had been
       concatenated  together.   This  is  useful  for   building
       libraries of AWK functions, without having to include them
       in each new AWK program that uses them.  It also  provides
       the  ability  to  mix  library functions with command line
       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 ``/'' charac­
       ter, no path search is performed.
       Gawk executes AWK programs in the following order.  First,
       all  variable  assignments specified via the -v option are
       performed.  Next, gawk compiles the program into an inter­
       nal  form.   Then,  gawk  executes  the  code in the BEGIN
       block(s) (if any), and then proceeds  to  read  each  file
       named  in  the ARGV array.  If there are no files named on
       the command line, gawk reads the standard input.
       If a filename on the command line has the form var=val  it
       is treated as a variable assignment. The variable var will
       be assigned the value val.  (This happens after any  BEGIN
       block(s) have been run.)  Command line variable assignment
       is most useful for dynamically  assigning  values  to  the
       variables  AWK  uses  to  control how input is broken into
       fields and records. It  is  also  useful  for  controlling
       state  if  multiple  passes  are needed over a single data
       (""), gawk skips over it.
       For  each  record  in  the  input, gawk tests to see if it
       matches any pattern in the AWK program.  For each  pattern
       that  the  record  matches,  the associated action is exe­
       cuted.  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).


       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.
       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  charac­
       ter, that character separates records.  Otherwise, RS is a
       regular expression.  Text in the input that  matches  this
       regular  expression will separate the record.  However, in
       compatibility 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 addition to  whatever
       value FS may have.
       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 sepa­
       rated by that character.  If FS is the null  string,  then
       each  individual character becomes a separate field.  Oth­
       erwise, FS is expected to be a  full  regular  expression.
       In  the special case that FS is a single space, fields are
       separated by runs of spaces and/or tabs  and/or  newlines.
       (But see the discussion of --posix, below).  Note 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 expected to have fixed
       width, and gawk will split up the record using the  speci­
       fied widths.  The value of FS is ignored.  Assigning a new
       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
       References to non-existent fields (i.e. fields after  $NF)
       produce the null-string. However, assigning to a non-exis­
       tent 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.  Ref­
       erences 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
       ARGIND      The  index  in  ARGV of the current file being
       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
       ENVIRON     An array containing the values of the  current
                   environment.   The  array  is  indexed  by the
                   environment variables, each element being  the
                   value  of that variable (e.g., ENVIRON["HOME"]
                   might be /home/arnold).  Changing  this  array
                   does  not  affect the environment seen by pro­
                   grams which gawk spawns via redirection or the
                   system()  function.   (This  may  change  in a
                   future version of gawk.)
                   rection  for  getline,  during a read for get­
                   line, or during a  close(),  then  ERRNO  will
                   contain a string describing the error.
       FIELDWIDTHS A  white-space  separated list of fieldwidths.
                   When set, gawk parses the input into fields of
                   fixed width, instead of using the value of the
                   FS variable as the field separator.  The fixed
                   field  width  facility  is still experimental;
                   the semantics may change as gawk evolves  over
       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
       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 IGNORE­
                   CASE has a non-zero value, then string compar­
                   isons  and  pattern  matching  in rules, field
                   splitting with FS, record separating with  RS,
                   regular expression matching with ~ and !~, and
                   the  gensub(),   gsub(),   index(),   match(),
                   split(),  and sub() 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 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 ver­
                   sions  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
       NR          The total number of input records seen so far.
       OFMT        The  output  format  for  numbers,  "%.6g", by

       ORS         The output record separator, by default a new­
       RS          The input record separator, by default a  new­
       RT          The  record  terminator.   Gawk sets RT to the
                   input text that matched the character or regu­
                   lar 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 sub­
                   scripts in array elements, by default  "\034".
       Arrays  are  subscripted with an expression between square
       brackets ([ and ]).  If the expression  is  an  expression
       list  (expr,  expr  ...)   then  the  array subscript is a
       string consisting of the  concatenation  of  the  (string)
       value  of  each  expression, separated by the value of the
       SUBSEP variable.  This facility is used to simulate multi­
       ply dimensioned arrays. For example:
              i = "A"; j = "B"; k = "C"
              x[i, j, k] = "hello, world\n"
       assigns  the string "hello, world\n" to the element of the
       array x which is indexed by the string "A\034B\034C".  All
       arrays in AWK are associative, i.e. indexed by string val­
       The special operator in may be used  in  an  if  or  while
       statement  to see if an array has an index consisting of a
       particular value.
              if (val in array)
                   print array[val]
       If the array has multiple subscripts, use (i, j) in array.
       The in construct may also be used in a for loop to iterate
       over all the elements of an array.
       An element may be deleted from an array using  the  delete
       statement.   The  delete  statement  may  also  be used to
       delete the entire contents of an array, just by specifying
       Variables  and  fields may be (floating point) numbers, or
       strings, or both. How the value of a  variable  is  inter­
       preted  depends  upon  its  context.  If used in a numeric
       expression, it will be treated as a number, if used  as  a
       string it will be treated as a string.
       To  force  a  variable to be treated as a number, add 0 to
       it; to force it to be treated as a string, concatenate  it
       with the null string.
       When  a  string must be converted to a number, the conver­
       sion is accomplished using atof(3).  A number is converted
       to  a  string  by  using  the value of CONVFMT as a format
       string for sprintf(3), with the numeric value of the vari­
       able as the argument.  However, even though all numbers in
       AWK are floating-point, integral values  are  always  con­
       verted as integers.  Thus, given
              CONVFMT = "%2.2f"
              a = 12
              b = a ""
       the variable b has a string value of "12" and not "12.00".
       Gawk performs comparisons as follows: If two variables are
       numeric,  they  are compared numerically.  If one value is
       numeric and the  other  has  a  string  value  that  is  a
       ``numeric string,'' then comparisons are also done numeri­
       cally.  Otherwise, the numeric value  is  converted  to  a
       string  and a string comparison is performed.  Two strings
       are compared, of course, as  strings.   According  to  the
       POSIX standard, even if two strings are numeric strings, a
       numeric comparison is performed.  However, this is clearly
       incorrect, and gawk does not do this.
       Note  that string constants, such as "57", are not numeric
       strings, they are string constants.  The idea of ``numeric
       string''  only applies to fields, getline input, FILENAME,
       ARGV elements, ENVIRON elements and  the  elements  of  an
       array  created  by  split() that are numeric strings.  The
       basic idea is that user input, and only user  input,  that
       looks numeric, should be treated that way.
       Uninitialized  variables  have the numeric value 0 and the
       string value "" (the null, or empty, string).


       AWK is a line oriented language. The pattern comes  first,
       and  then  the action. Action statements are enclosed in {
       and }.  Either the pattern may be missing, or  the  action
       may  be  missing, but, of course, not both. If the pattern
       is missing, the action will be executed for  every  single
       which prints the entire record.
       Comments  begin  with  the  ``#''  character, and continue
       until the end of the line.  Blank lines  may  be  used  to
       separate  statements.   Normally,  a statement ends with a
       newline, however, this is not the case for lines ending in
       a  ``,'',  {, ?, :, &&, or ||.  Lines ending in do or else
       also have their statements automatically continued on  the
       following  line.   In other cases, a line can be continued
       by ending it with a ``\'', in which case the newline  will
       be ignored.
       Multiple  statements  may be put on one line by separating
       them with a ``;''.  This applies to  both  the  statements
       within the action part of a pattern-action pair (the usual
       case), and to the pattern-action statements themselves.
       AWK patterns may be one of the following:
              /regular expression/
              relational expression
              pattern && pattern
              pattern || pattern
              pattern ? pattern : pattern
              ! pattern
              pattern1, pattern2
       BEGIN and END are two special kinds of patterns which  are
       not  tested  against  the  input.  The action parts of all
       BEGIN patterns are merged as if  all  the  statements  had
       been  written  in  a single BEGIN block. They are executed
       before any of the input is read. Similarly,  all  the  END
       blocks  are  merged,  and  executed  when all the input is
       exhausted (or when an exit statement is executed).   BEGIN
       and END patterns cannot be combined with other patterns in
       pattern expressions.  BEGIN and END patterns  cannot  have
       missing action parts.
       For  /regular  expression/ patterns, the associated state­
       ment is executed for each input record  that  matches  the
       regular  expression.   Regular expressions are the same as
       those in egrep(1), and are summarized below.
       A relational expression  may  use  any  of  the  operators
       defined  below in the section on actions.  These generally
       test whether certain fields match certain regular  expres­
       and logical NOT, respectively, as in C.   They  do  short-
       circuit evaluation, also as in C, and are used for combin­
       ing more primitive pattern expressions. As  in  most  lan­
       guages,  parentheses  may  be  used to change the order of
       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  com­
       bine with any other sort of pattern expression.
   Regular Expressions
       Regular  expressions are the extended kind found in egrep.
       They are composed of characters as follows:
       c          matches the non-metacharacter c.
       \c         matches the literal character c.
       .          matches any character including newline.
       ^          matches the beginning of a string.
       $          matches the end of a string.
       [abc...]   character list, matches any of  the  characters
       [^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,m}     One or two  numbers  inside  braces  denote  an
                  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  begin­
                  ning or the end of a word.
       \B         matches the empty string within a word.
       \<         matches  the empty string at the beginning of a
       \>         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-con­
       \`         matches  the empty string at the beginning of a
                  buffer (string).
       \'         matches the  empty  string  at  the  end  of  a
       The  escape  sequences  that are valid in string constants
       (see below) are also legal in regular expressions.
       Character classes are a  new  feature  introduced  in  the
       POSIX  standard.   A character class is a special notation
       for describing lists of 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 character 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
       character classes defined by the POSIX standard.
              Alphanumeric characters.
              Alphabetic characters.
              Space or tab characters.
              Control characters.
              Numeric characters.
              Characters that are both printable and visible.  (A
              space is printable, but not visible, while an a  is
              Lower-case alphabetic characters.
              Printable  characters (characters that are not con­
              trol characters.)
              Punctuation characters  (characters  that  are  not
              letter,  digits, control characters, or space char­
              Space characters (such as space, tab, and formfeed,
              to name a few).
              Upper-case alphabetic characters.
              Characters that are hexadecimal digits.
       For  example, before the POSIX standard, to match alphanu­
       meric  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
       represented with more than one character, as well as  sev­
       eral  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
              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 charac­
       ter  classes;  they  do not recognize collating symbols or
       equivalence classes.
       The \y, \B, \<, \>, \w, \W, \`, and \' operators are  spe­
       cific  to gawk; they are extensions based on facilities in
       the GNU regexp libraries.
       The various command line options control how  gawk  inter­
       prets characters in regexps.
       No options
              In  the  default case, gawk provide all the facili­
              ties of POSIX regexps and the GNU regexp  operators
              described above.  However, interval expressions are
              not supported.
              Only POSIX regexps are supported, the GNU operators
              are  not  special.  (E.g., \w matches a literal w).
              Interval expressions are allowed.
              Traditional Unix awk regexps are matched.  The  GNU
              operators are not special, interval expressions are
              not available, and neither are the POSIX  character
              classes   ([[:alnum:]]   and  so  on).   Characters
              described by octal and hexadecimal escape sequences
              are  treated literally, even if they represent reg­
              exp metacharacters.
              Allow interval  expressions  in  regexps,  even  if
              --traditional has been provided.
       Action statements are enclosed in braces, { and }.  Action
       statements consist of the usual  assignment,  conditional,
       and looping statements found in most languages. The opera­
       tors,  control  statements,  and  input/output  statements
       available are patterned after those in C.
       The  operators  in AWK, in order of decreasing precedence,
       (...)       Grouping
       $           Field reference.
       ++ --       Increment and decrement, both prefix and post­
       ^           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, other­
                   wise 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
              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
       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 pro­
                             gram. 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),
                             two words. While this usage is still
                             recognized,  it  generates a warning
                             message  and  will   eventually   be
       print                 Prints the current record.  The out­
                             put 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 ter­
                             minated with the value  of  the  ORS
       print expr-list >file Prints  expressions  on  file.  Each
                             expression is separated by the value
                             of  the  OFS  variable.  The  output
                             record is terminated with the  value
                             of the ORS variable.
       printf fmt, expr-list Format and print.
       printf fmt, expr-list >file
                             Format and print on file.
       system(cmd-line)      Execute  the  command  cmd-line, and
                             return the exit status.   (This  may
                             not  be  available on non-POSIX sys­
       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
       Other input/output  redirections  are  also  allowed.  For
       print and printf, >>file appends output to the file, while
       | command writes on a pipe.  In a similar fashion, command
       |  getline  pipes  into getline.  The getline command will
       return 0 on end of file, and -1 on an error.
   The printf Statement
       The AWK versions of the  printf  statement  and  sprintf()
       function (see below) accept the following conversion spec­
       ification formats:
       %c     An ASCII character.  If the argument used for %c is
              numeric,  it is treated as a character and printed.
       %i     A decimal number (the integer part).
       %E     A   floating   point    number    of    the    form
              [-]d.dddddde[+-]dd.   The  %E format uses E instead
              of e.
       %f     A floating point number of the form  [-]ddd.dddddd.
       %G     Use %e or %f conversion, whichever is shorter, with
              nonsignificant zeros  suppressed.   The  %G  format
              uses %E instead of %e.
       %o     An unsigned octal number (again, an integer).
       %s     A character string.
       %X     An  unsigned  hexadecimal  number (an integer).  %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 letter:
       -      The  expression should be left-justified within its
       space  For numeric  conversions,  prefix  positive  values
              with  a  space,  and  negative  values with a minus
       +      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 let­
              ters.  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  zeroes instead of
              spaces.  This applies even  to  non-numeric  output
       width  The field should be padded to this width. The field
              is normally padded with spaces.  If the 0 flag  has
              been used, it is padded with zeroes.
       .prec  A  number  that specifies the precision to use when
              printing.  For the %e, %E,  and  %f  formats,  this
              specifies  the number of digits you want printed to
              the right of the decimal point.  For the %g, and %G
              formats, it specifies the maximum number of signif­
              icant digits.  For the %d, %o, %i, %u, %x,  and  %X
              formats,  it specifies the minimum number of digits
              to print.  For a string, it specifies  the  maximum
              number of characters from the string that should be
       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 filenames are:
       /dev/pid    Reading this file returns the  process  ID  of
                   the  current  process,  in decimal, terminated
                   with a newline.
       /dev/ppid   Reading this file returns the  parent  process
                   ID  of the current process, in decimal, termi­
                   nated with a newline.
       /dev/pgrpid Reading this file returns the process group ID
                   of the current process, in decimal, terminated
                   with a newline.
       /dev/user   Reading this file returns a single record ter­
                   minated  with a newline.  The fields are sepa­
                   rated with spaces.  $1 is  the  value  of  the
                   getuid(2)  system call, $2 is the value of the
                   geteuid(2) system call, $3 is the value of the
                   getgid(2)  system call, and $4 is the value of
                   the getegid(2) system call.  If there are  any
                   additional  fields,  they  are  the  group IDs
                   returned by getgroups(2).  Multiple groups may
                   not be supported on all systems.
       /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
              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
       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 radi­
       sqrt(expr)    the square root function.
       srand([expr]) uses expr as a new seed for the random  num­
                     ber  generator.  If no expr is provided, the
                     time of day will be used.  The return  value
                     is  the  previous seed for the random number
   String Functions
       Gawk has the following pre-defined string functions:
                               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  sup­
                               plied, $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  indi­
                               cate  just  the  text that matched
                               the n'th parenthesized  subexpres­
                               sion.  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 AWK Language Pro­
                               gramming for a  fuller  discussion
                               of  the  rules  for  &'s and back­
                               slashes 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
       length([s])             returns  the  length of the string
                               s, or the length of $0 if s is not
       match(s, r)             returns  the  position  in s where
                               the regular expression  r  occurs,
                               or 0 if r is not present, and sets
                               the values of RSTART and  RLENGTH.
       split(s, a [, r])       splits the string s into the array
                               a on the regular expression r, and
                               returns the number of fields. If r
                               is omitted, FS  is  used  instead.
                               The  array  a  is  cleared  first.
                               Splitting behaves  identically  to
                               and  returns the resulting string.
       sub(r, s [, t])         just like  gsub(),  but  only  the
                               first    matching   substring   is
       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
       tolower(str)            returns  a copy of the string str,
                               with all the upper-case characters
                               in  str translated to their corre­
                               sponding lower-case  counterparts.
                               Non-alphabetic characters are left
       toupper(str)            returns a copy of the string  str,
                               with all the lower-case characters
                               in str translated to their  corre­
                               sponding  upper-case counterparts.
                               Non-alphabetic characters are left
   Time Functions
       Since  one of the primary uses of AWK programs is process­
       ing log files that contain time  stamp  information,  gawk
       provides  the  following  two functions for obtaining time
       stamps and formatting them.
       systime() returns the current time of day as the number of
                 seconds  since  the Epoch (Midnight UTC, January
                 1, 1970 on POSIX systems).
       strftime([format [, timestamp]])
                 formats timestamp according to the specification
                 in  format.  The timestamp should be of the same
                 form as returned by systime().  If timestamp  is
                 missing,  the  current  time of day is used.  If
                 format is missing, a default  format  equivalent
                 to  the output of date(1) will be used.  See the
                 specification for  the  strftime()  function  in
                 ANSI C for the format conversions that are guar­
                 anteed to be available.  A public-domain version
                 of  strftime(3)  and a man page for it 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
       tain escape sequences are recognized, as in C. These are:
       \\   A literal backslash.
       \a   The ``alert'' character; usually the ASCII BEL  char­
       \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 hexadeci­
            mal digits following the \x.  As in ANSI C, all  fol­
            lowing  hexadecimal digits are considered part of the
            escape sequence.  (This feature should tell us  some­
            thing  about  language  design  by committee.)  E.g.,
            "\x1B" is the ASCII ESC (escape) character.
       \ddd The character represented by the 1-, 2-,  or  3-digit
            sequence  of  octal  digits. E.g. "\033" is the ASCII
            ESC (escape) character.
       \c   The literal character c.
       The escape sequences may also be used inside constant reg­
       ular expressions (e.g., /[ \t\f\n\r\v]/ matches whitespace
       In compatibility mode, the characters represented by octal
       and  hexadecimal  escape  sequences  are treated literally
       when used in regexp constants. Thus, /a\52b/ is equivalent
       to /a\*b/.


       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 parame­
       ters supplied in the function call are used to instantiate
       the formal parameters declared in  the  function.   Arrays
       Since functions were not originally part of the  AWK  lan­
       guage, the provision for local variables is rather clumsy:
       They are declared as extra  parameters  in  the  parameter
       list.  The  convention is to separate local variables from
       real parameters by extra spaces in the parameter list. For
              function  f(p, q,     a, b)   # a & b are local
              /abc/     { ... ; f(1, 2) ; ... }
       The  left  parenthesis  in  a function call is required to
       immediately follow the function name, without  any  inter­
       vening  white space.  This is to avoid a syntactic ambigu­
       ity with the  concatenation  operator.   This  restriction
       does not apply to the built-in functions listed above.
       Functions may call each other and may be recursive.  Func­
       tion parameters used as local variables are initialized to
       the  null string and the number zero upon function invoca­
       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
       The word func may be used in place of function.


       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 }



       egrep(1),  getpid(2),  getppid(2),  getpgrp(2), getuid(2),
       geteuid(2), getgid(2), getegid(2), getgroups(2)
       The AWK Programming Language,  Alfred  V.  Aho,  Brian  W.
       Kernighan, Peter J. Weinberger, Addison-Wesley, 1988. ISBN
       AWK Language Programming, Edition 1.0,  published  by  the
       Free Software Foundation, 1995.


       A  primary  goal  for gawk is compatibility with the POSIX
       standard, as well as with the latest version of UNIX  awk.
       To  this end, gawk incorporates the following user visible
       features which are not described in the AWK book, but  are
       part of the Bell Labs version of awk, and are in the POSIX
       The -v option for assigning variables before program  exe­
       cution  starts  is  new.   The book indicates that command
       line variable assignment happens when awk would  otherwise
       open  the  argument  as  a  file, which is after the BEGIN
       block is executed.  However, in  earlier  implementations,
       when  such  an  assignment appeared before any file names,
       the assignment would happen before  the  BEGIN  block  was
       run.   Applications  came  to  depend on this ``feature.''
       When awk was changed  to  match  its  documentation,  this
       option was added to accommodate applications that depended
       upon the old behavior.  (This feature was agreed  upon  by
       both the AT&T and GNU developers.)
       The -W option for implementation specific features is from
       the POSIX standard.
       When processing arguments, gawk uses  the  special  option
       ``--''  to  signal the end of arguments.  In compatibility
       mode, it will warn about, but otherwise ignore,  undefined
       options.   In  normal operation, such arguments are passed
       on to the AWK program for it to process.
       The AWK book does not define the return value of  srand().
       The POSIX standard has it return the seed it was using, to
       allow keeping track of random number sequences.  Therefore
       srand() in gawk also returns its current seed.
       Other  new  features  are:  The use of multiple -f options
       (from MKS awk); the ENVIRON array; the \a, and  \v  escape
       sequences  (done  originally  in  gawk  and  fed back into
       AT&T's); the tolower() and  toupper()  built-in  functions
       (from  AT&T);  and the ANSI C conversion specifications in
       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  --tradi­
       tional option.
       The  following features of gawk are not available in POSIX
              · The \x escape sequence.  (Disabled with --posix.)
              · The  fflush() function.  (Disabled with --posix.)
              · The systime(),  strftime(),  and  gensub()  func­
              · The special file names available for I/O redirec­
                tion are not recognized.
              · The ARGIND, ERRNO, and RT variables are not  spe­
              · The  IGNORECASE variable and its side-effects are
                not available.
              · The FIELDWIDTHS variable  and  fixed-width  field
              · The use of RS as a regular expression.
              · The  ability  to  split out individual characters
                using the null string as the value of FS, and  as
                the third argument to split().
              · No  path  search is performed for files named via
                the -f option.  Therefore the AWKPATH environment
                variable is not special.
              · The  use of nextfile to abandon processing of the
                current input file.
              · The use of delete array to delete the entire con­
                tents of an array.
       The  AWK  book  does  not  define  the return value of the
       close() function.  Gawk's close() returns the  value  from
       fclose(3),  or  pclose(3),  when  closing  a file or pipe,
       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
       ior also does not occur if --posix has been specified.  To
       really  get  a tab character as the field separator, it is
       best to use quotes: gawk -F'\t' ....


       There are two features of historical  AWK  implementations
       that  gawk  supports.   First,  it is possible to call the
       length() built-in function not only with no argument,  but
       even without parentheses!  Thus,
              a = length     # 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 warning about its  use  if
       --lint is specified on the command line.
       The other feature is the use of either the continue or the
       break statements outside the body of a while, for,  or  do
       loop.   Traditional  AWK implementations have treated such
       usage as equivalent to the next statement.  Gawk will sup­
       port this usage if --traditional has been specified.


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


       The -F option is not  necessary  given  the  command  line
       variable assignment feature; it remains only for backwards
       If your system actually has support for  /dev/fd  and  the
       associated /dev/stdin, /dev/stdout, and /dev/stderr files,
       you may get different output from gawk than you would  get
       on  a  system  without  those files.  When gawk interprets
       these files internally,  it  synchronizes  output  to  the
       standard  output  with  output  to /dev/stdout, while on a
       system with those files, the output is actually to differ­
       ent open files.  Caveat Emptor.
       Syntactically  invalid  single  character programs tend to
       diagnose in the completely general case, and the effort to
       do so really is not worth it.


       This man page documents gawk, version 3.0.4.


       The  original  version of UNIX awk was designed and imple­
       mented  by  Alfred  Aho,  Peter  Weinberger,   and   Brian
       Kernighan  of AT&T Bell Labs. Brian Kernighan continues to
       maintain and enhance it.
       Paul Rubin and Jay Fenlason, of the Free Software  Founda­
       tion,  wrote gawk, to be compatible with the original ver­
       sion of awk distributed in  Seventh  Edition  UNIX.   John
       Woods  contributed  a number of bug fixes.  David Trueman,
       with contributions from Arnold Robbins, made gawk compati­
       ble  with  the new version of UNIX awk.  Arnold Robbins is
       the current maintainer.
       The initial DOS port was done by  Conrad  Kwok  and  Scott
       Garfinkle.   Scott  Deifik  is the current DOS maintainer.
       Pat Rankin did the port to VMS, and Michal Jaegermann  did
       the  port  to  the Atari ST.  The port to OS/2 was done by
       Kai Uwe Rommel, with contributions and  help  from  Darrel
       Hankerson.  Fred Fish supplied support for the Amiga.


       If  you find a bug in gawk, please send electronic mail to,   with    a    carbon    copy    to   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  refer­
       ence  manual carefully to be sure that what you think is a
       bug really is, instead of just a quirk in the language.
       Whatever  you  do,  do  NOT   post   a   bug   report   in
       comp.lang.awk.   While  the  gawk  developers occasionally
       read this newsgroup, posting bug reports there is an unre­
       liable  way  to report bugs. Instead, please use the elec­
       tronic mail addresses given above.


       Brian Kernighan of Bell Labs provided valuable  assistance
       during testing and debugging.  We thank him.
       Copyright  ©) 1996,97,98,99 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 ver­
       sions  of this manual page under the conditions for verba­
       tim 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 permis­
       sion notice may be stated in a translation approved by the


Comments - most recent first
(Please feel free to answer questions posted by others!)

Narges     (14 Aug 2012, 20:56)
Use full page but pls add examples. Takes less time to figure out the codes with examples.
Cialis     (12 Feb 2012, 23:40)
letter of thanks for publishing this entry. It is really essential for me.
afsar     (04 Feb 2011, 04:53)
it is very useful
add some more example long with them
Shashi Kuamr     (29 Mar 2010, 12:31)
This is sufficient and satisfying note on awk prog this is very usefull and thank for this info.

I welcome your comments. However... I am puzzled by many people who say "Please send me the Linux tutorial." This website *is* your Linux Tutorial! Read everything here, learn all you can, ask questions if you like. But don't ask me to send what you already have. :-)

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