Skip site navigation (1)Skip section navigation (2)

FreeBSD Man Pages

Man Page or Keyword Search:
Man Architecture
Apropos Keyword Search (all sections) Output format
home | help
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 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.

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 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.

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 implementations.

       -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, newline 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 intermixing of library functions (used via the -f and
              --file options) with source code entered on the command line.
              It is intended primarily for medium to large AWK programs used
              in shell scripts.

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

       --     Signal the end of options.  This is useful to allow further
              arguments to the AWK program itself to start with a "-".  This
              is mainly for consistency with the argument parsing convention
              used by most other POSIX programs.

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

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

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

       Gawk first reads the program source from the program-file(s) if
       specified, from arguments to --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 programs.

       The environment variable AWKPATH specifies a search path to use when
       finding source files named with the -f option.  If this variable does
       not exist, the default path is ".:/usr/local/share/awk".  (The actual
       directory may vary, depending upon how gawk was built and installed.)
       If a file name given to the -f option contains a "/" character, no path
       search is performed.

       Gawk executes AWK programs in the following order.  First, all variable
       assignments specified via the -v option are performed.  Next, gawk
       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 assignment.  The variable var will be assigned the value
       val.  (This happens after any BEGIN block(s) have been run.)  Command
       line variable assignment is most useful for dynamically assigning
       values to the variables AWK uses to control how input is broken into
       fields and records.  It is also useful for controlling state if
       multiple passes are needed over a single data file.

       If the value of a particular element of ARGV is empty (""), gawk skips
       over it.

       For each 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 executed.  The patterns are tested in the
       order they occur in the program.

       Finally, after all the input is exhausted, gawk executes the code in
       the END block(s) (if any).

VARIABLES, RECORDS AND FIELDS
       AWK variables are dynamic; they come into existence when they are first
       used.  Their values are either floating-point numbers or strings, or
       both, depending upon how they are used.  AWK also has one dimensional
       arrays; arrays with multiple dimensions may be simulated.  Several pre-
       defined variables are set as a program runs; these will be described as
       needed and summarized below.

   Records
       Normally, records are separated by newline characters.  You can control
       how records are separated by assigning values to the built-in variable
       RS.  If RS is any single character, that character separates records.
       Otherwise, RS is a regular expression.  Text in the input that matches
       this regular expression 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.

   Fields
       As each input record is read, gawk splits the record into fields, using
       the value of the FS variable as the field separator.  If FS is a single
       character, fields are separated by that character.  If FS is the null
       string, then each individual character becomes a separate field.
       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 expected 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.  However, assigning to a non-existent field (e.g., $(NF+2)
       = 5) will increase the value of NF, create any intervening fields with
       the null string as their value, and cause the value of $0 to be
       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 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 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 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 variables, the initial value of IGNORECASE is
                  zero, so all regular expression and string operations are
                  normally case-sensitive.  Under Unix, the full ISO 8859-1
                  Latin-1 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 character 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 default "\034".

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

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

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

       An element may be deleted from an array using the delete statement.
       The delete statement may also be used to delete the entire contents of
       an array, just by specifying the array name without a subscript.

   Variable Typing And Conversion
       Variables and fields may be (floating point) numbers, or strings, or
       both.  How the value of a variable is interpreted depends upon its
       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 numerically.  If one value is numeric and the other
       has a string value that is a "numeric string," then comparisons are
       also done numerically.  Otherwise, the numeric value is converted to a
       string and a string comparison is performed.  Two strings are compared,
       of course, as strings.  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).

PATTERNS AND ACTIONS
       AWK is a line-oriented language.  The pattern comes first, and then the
       action.  Action statements are enclosed in { and }.  Either the pattern
       may be missing, or the action may be missing, but, of course, not both.
       If the pattern is missing, the action will be executed for every single
       record of input.  A missing action is equivalent to

              { print }

       which prints the entire record.

       Comments begin with the "#" character, and continue until the end of
       the line.  Blank lines may be used to separate statements.  Normally, a
       statement ends with a newline, however, this is not the case for lines
       ending in a ",", {, ?, :, &&, or ||.  Lines ending in do or else also
       have their statements automatically continued on the following line.
       In other cases, a line can be continued by ending it with a "\", in
       which case the newline will be ignored.

       Multiple statements may be put on one line by separating them with a
       ";".  This applies to both the statements within the action part of a
       pattern-action pair (the usual case), and to the pattern-action
       statements themselves.

   Patterns
       AWK patterns may be one of the following:

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

       BEGIN and END are two special kinds of patterns which are not tested
       against the input.  The action parts of all BEGIN patterns are merged
       as if all the statements had been written in a single BEGIN block.
       They are executed before any of the input is read.  Similarly, all the
       END blocks are merged, and executed when all the input is exhausted (or
       when an exit statement is executed).  BEGIN and END patterns cannot be
       combined with other patterns in pattern expressions.  BEGIN and END
       patterns cannot have missing action parts.

       For /regular expression/ patterns, the associated statement is executed
       for each input record that matches the regular expression.  Regular
       expressions are the same as those in egrep(1), and are summarized
       below.

       A relational expression may use any of the operators defined below in
       the section on actions.  These generally test whether certain fields
       match certain regular expressions.

       The &&, ||, and !  operators are logical AND, logical OR, and logical
       NOT, respectively, as in C.  They do short-circuit evaluation, also as
       in C, and are used for combining more primitive pattern expressions.
       As in most languages, parentheses may be used to change the order of
       evaluation.

       The ?: operator is like the same operator in C.  If the first pattern
       is true then the pattern used for testing is the second pattern,
       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
       expression.

   Regular Expressions
       Regular expressions are the extended kind found in egrep.  They are
       composed of characters as follows:

       c          matches the non-metacharacter c.

       \c         matches the literal character c.

       .          matches any character including newline.

       ^          matches the beginning of a string.

       $          matches the end of a string.

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

       [^abc...]  negated character list, matches any character except abc....

       r1|r2      alternation: matches either r1 or r2.

       r1r2       concatenation: matches r1, and then r2.

       r+         matches one or more r's.

       r*         matches zero or more r's.

       r?         matches zero or one r's.

       (r)        grouping: matches r.

       r{n}
       r{n,}
       r{n,m}     One or two numbers inside braces denote an interval
                  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 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.

       [: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 represented 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, 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 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 instead 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 suppressed.  The %G format uses %E instead
              of %e.

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

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

       %s     A character string.

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

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

       There are optional, additional parameters that may lie between the %
       and the control letter:

       -      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 zeroes instead of spaces.  This applies even to
              non-numeric output formats.  This flag only has an effect when
              the field width is wider than the value to be printed.

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

       .prec  A number that specifies the precision to use when printing.  For
              the %e, %E, and %f formats, this specifies the number of digits
              you want printed to the right of the decimal point.  For the %g,
              and %G formats, it specifies the maximum number of significant
              digits.  For the %d, %o, %i, %u, %x, and %X formats, it
              specifies the minimum 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 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, terminated 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 terminated with a
                  newline.  The fields are separated with spaces.  $1 is the
                  value of the getuid(2) system call, $2 is the value of the
                  geteuid(2) system call, $3 is the value of the getgid(2)
                  system call, and $4 is the value of the getegid(2) system
                  call.  If there are any additional fields, they are the
                  group IDs returned by getgroups(2).  Multiple groups may not
                  be supported on all systems.

       /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 provided, 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
                                 substitutions.  If t is not supplied, use $0.
                                 An & in the replacement text is replaced with
                                 the text that was actually matched.  Use \&
                                 to get a literal &.  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
                                 instead.  The array a is cleared first.
                                 Splitting behaves identically to field
                                 splitting, described above.

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

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

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

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

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

   Time Functions
       Since one of the primary uses of AWK programs is processing log files
       that contain time stamp information, gawk provides the following 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 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 sequence.  (This feature should
            tell us something about language design by committee.)  E.g.,
            "\x1B" is the ASCII ESC (escape) character.

       \ddd The character represented by the 1-, 2-, or 3-digit sequence of
            octal digits.  E.g., "\033" is the ASCII ESC (escape) character.

       \c   The literal character c.

       The escape sequences may also be used inside constant regular
       expressions (e.g., /[ \t\f\n\r\v]/ matches whitespace characters).

       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
       Functions in AWK are defined as follows:

              function name(parameter list) { statements }

       Functions are executed when they are called from within expressions in
       either patterns or actions.  Actual parameters supplied in the function
       call are used to instantiate the formal parameters declared in the
       function.  Arrays are passed by reference, other variables are passed
       by value.

       Since functions were not originally part of the AWK language, the
       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, Addison-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 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 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
       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
       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 option.

       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() returns 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 separator, 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 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 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 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.

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

       If your system actually has support for /dev/fd and the associated
       /dev/stdin, /dev/stdout, and /dev/stderr files, you may get different
       output from gawk than you would get on a system without those files.
       When gawk interprets these files internally, it synchronizes output to
       the standard output with output to /dev/stdout, while on a system with
       those files, the output is actually to different open files.  Caveat
       Emptor.

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

VERSION INFORMATION
       This man page documents gawk, version 3.0.6.

AUTHORS
       The original version of UNIX awk was designed and implemented 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 Foundation, wrote
       gawk, to be compatible with the original version of awk distributed in
       Seventh Edition UNIX.  John Woods contributed a number of bug fixes.
       David Trueman, with contributions from Arnold Robbins, made gawk
       compatible 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.

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

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

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

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)

NAME | SYNOPSIS | DESCRIPTION | OPTION FORMAT | OPTIONS | AWK PROGRAM EXECUTION | VARIABLES, RECORDS AND FIELDS | PATTERNS AND ACTIONS | FUNCTIONS | EXAMPLES | SEE ALSO | POSIX COMPATIBILITY | GNU EXTENSIONS | HISTORICAL FEATURES | ENVIRONMENT VARIABLES | BUGS | VERSION INFORMATION | AUTHORS | BUG REPORTS | ACKNOWLEDGEMENTS | COPYING PERMISSIONS

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=awk&sektion=1&manpath=FreeBSD+4.7-RELEASE>

home | help