User-modified (The GNU Awk User’s Guide)
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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 section Command-Line Options), they are not special. (Any exceptions are noted in the description of each variable.)
BINMODE #
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 section Other Freely Available awk Implementations) also supports this variable, but only using numeric values.
CONVFMT
A string that controls the conversion of numbers to strings (see section Conversion of Strings and Numbers). It works by being passed, in effect, as the first argument to the sprintf()
function (see section String-Manipulation Functions). Its default value is "%.6g"
. CONVFMT
was introduced by the POSIX standard.
FIELDWIDTHS #
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 section Reading Fixed-Width Data for more information.
FPAT #
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 section Defining Fields by Content for more information.
FS
The input field separator (see section 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 " "
/@w , 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.
IGNORECASE #
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 section Case Sensitivity in Matching.
LINT #
When this variable is true (nonzero or non-null), gawk
behaves as if the --lint
command-line option is in effect (see section 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.
OFMT
A string that controls conversion of numbers to strings (see section 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 section 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
.
OFS
The output field separator (see section Output Separators). It is output between the fields printed by a print
statement. Its default value is " "
/@w , a string consisting of a single space.
ORS
The output record separator. It is output at the end of every print
statement. Its default value is "\n"
, the newline character. (See section Output Separators.)
PREC #
The working precision of arbitrary-precision floating-point numbers, 53 bits by default (see section Setting the Precision).
ROUNDMODE #
The rounding mode to use for arbitrary-precision arithmetic on numbers, by default "N"
(roundTiesToEven
in the IEEE 754 standard; see section Setting the Rounding Mode).
RS
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 section 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 section Command-Line Options), just the first character of RS
’s value is used.
SUBSEP
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 section Multidimensional Arrays).
TEXTDOMAIN #
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 section Internationalization with gawk). The default value of TEXTDOMAIN
is "messages"
.
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