7.5.1 Built-in Variables That Control awk

The following is an alphabetical list of variables that you can change to control how awk does certain things.

The variables that are specific to gawk are marked with a pound sign (‘#’). These variables are gawk extensions. In other awk implementations or if gawk is in compatibility mode (see Command-Line Options), they are not special. (Any exceptions are noted in the description of each variable.)


On non-POSIX systems, this variable specifies use of binary mode for all I/O. Numeric values of one, two, or three specify that input files, output files, or all files, respectively, should use binary I/O. A numeric value less than zero is treated as zero, and a numeric value greater than three is treated as three. Alternatively, string values of "r" or "w" specify that input files and output files, respectively, should use binary I/O. A string value of "rw" or "wr" indicates that all files should use binary I/O. Any other string value is treated the same as "rw", but causes gawk to generate a warning message. BINMODE is described in more detail in Using gawk on PC Operating Systems. mawk (see Other Freely Available awk Implementations) also supports this variable, but only using numeric values.


A string that controls the conversion of numbers to strings (see Conversion of Strings and Numbers). It works by being passed, in effect, as the first argument to the sprintf() function (see String-Manipulation Functions). Its default value is "%.6g". CONVFMT was introduced by the POSIX standard.


A space-separated list of columns that tells gawk how to split input with fixed columnar boundaries. Starting in version 4.2, each field width may optionally be preceded by a colon-separated value specifying the number of characters to skip before the field starts. Assigning a value to FIELDWIDTHS overrides the use of FS and FPAT for field splitting. See Reading Fixed-Width Data for more information.


A regular expression (as a string) that tells gawk to create the fields based on text that matches the regular expression. Assigning a value to FPAT overrides the use of FS and FIELDWIDTHS for field splitting. See Defining Fields by Content for more information.


The input field separator (see Specifying How Fields Are Separated). The value is a single-character string or a multicharacter regular expression that matches the separations between fields in an input record. If the value is the null string (""), then each character in the record becomes a separate field. (This behavior is a gawk extension. POSIX awk does not specify the behavior when FS is the null string. Nonetheless, some other versions of awk also treat "" specially.)

The default value is " ", a string consisting of a single space. As a special exception, this value means that any sequence of spaces, TABs, and/or newlines is a single separator. It also causes spaces, TABs, and newlines at the beginning and end of a record to be ignored.

You can set the value of FS on the command line using the -F option:

awk -F, 'program' input-files

If gawk is using FIELDWIDTHS or FPAT for field splitting, assigning a value to FS causes gawk to return to the normal, FS-based field splitting. An easy way to do this is to simply say ‘FS = FS’, perhaps with an explanatory comment.


If IGNORECASE is nonzero or non-null, then all string comparisons and all regular expression matching are case-independent. This applies to regexp matching with ‘~’ and ‘!~’, the gensub(), gsub(), index(), match(), patsplit(), split(), and sub() functions, record termination with RS, and field splitting with FS and FPAT. However, the value of IGNORECASE does not affect array subscripting and it does not affect field splitting when using a single-character field separator. See Case Sensitivity in Matching.


When this variable is true (nonzero or non-null), gawk behaves as if the --lint command-line option is in effect (see Command-Line Options). With a value of "fatal", lint warnings become fatal errors. With a value of "invalid", only warnings about things that are actually invalid are issued. (This is not fully implemented yet.) Any other true value prints nonfatal warnings. Assigning a false value to LINT turns off the lint warnings.

This variable is a gawk extension. It is not special in other awk implementations. Unlike with the other special variables, changing LINT does affect the production of lint warnings, even if gawk is in compatibility mode. Much as the --lint and --traditional options independently control different aspects of gawk’s behavior, the control of lint warnings during program execution is independent of the flavor of awk being executed.


A string that controls conversion of numbers to strings (see Conversion of Strings and Numbers) for printing with the print statement. It works by being passed as the first argument to the sprintf() function (see String-Manipulation Functions). Its default value is "%.6g". Earlier versions of awk used OFMT to specify the format for converting numbers to strings in general expressions; this is now done by CONVFMT.


The output field separator (see Output Separators). It is output between the fields printed by a print statement. Its default value is " ", a string consisting of a single space.


The output record separator. It is output at the end of every print statement. Its default value is "\n", the newline character. (See Output Separators.)


The working precision of arbitrary-precision floating-point numbers, 53 bits by default (see Setting the Precision).


The rounding mode to use for arbitrary-precision arithmetic on numbers, by default "N" (roundTiesToEven in the IEEE 754 standard; see Setting the Rounding Mode).


The input record separator. Its default value is a string containing a single newline character, which means that an input record consists of a single line of text. It can also be the null string, in which case records are separated by runs of blank lines. If it is a regexp, records are separated by matches of the regexp in the input text. (See How Input Is Split into Records.)

The ability for RS to be a regular expression is a gawk extension. In most other awk implementations, or if gawk is in compatibility mode (see Command-Line Options), just the first character of RS’s value is used.


The subscript separator. It has the default value of "\034" and is used to separate the parts of the indices of a multidimensional array. Thus, the expression ‘foo["A", "B"]’ really accesses foo["A\034B"] (see Multidimensional Arrays).


Used for internationalization of programs at the awk level. It sets the default text domain for specially marked string constants in the source text, as well as for the dcgettext(), dcngettext(), and bindtextdomain() functions (see Internationalization with gawk). The default value of TEXTDOMAIN is "messages".