grep: Environment Variables
2.2 Environment Variables
=========================
The behavior of ‘grep’ is affected by the following environment
variables.
The locale for category ‘LC_FOO’ is specified by examining the three
environment variables ‘LC_ALL’, ‘LC_FOO’, and ‘LANG’, in that order.
The first of these variables that is set specifies the locale. For
example, if ‘LC_ALL’ is not set, but ‘LC_COLLATE’ is set to ‘pt_BR’,
then the Brazilian Portuguese locale is used for the ‘LC_COLLATE’
category. As a special case for ‘LC_MESSAGES’ only, the environment
variable ‘LANGUAGE’ can contain a colon-separated list of languages that
overrides the three environment variables that ordinarily specify the
‘LC_MESSAGES’ category. The ‘C’ locale is used if none of these
environment variables are set, if the locale catalog is not installed,
or if ‘grep’ was not compiled with national language support (NLS). The
shell command ‘locale -a’ lists locales that are currently available.
Many of the environment variables in the following list let you
control highlighting using Select Graphic Rendition (SGR) commands
interpreted by the terminal or terminal emulator. (See the section in
the documentation of your text terminal for permitted values and their
meanings as character attributes.) These substring values are integers
in decimal representation and can be concatenated with semicolons.
‘grep’ takes care of assembling the result into a complete SGR sequence
(‘\33[’...‘m’). Common values to concatenate include ‘1’ for bold, ‘4’
for underline, ‘5’ for blink, ‘7’ for inverse, ‘39’ for default
foreground color, ‘30’ to ‘37’ for foreground colors, ‘90’ to ‘97’ for
16-color mode foreground colors, ‘38;5;0’ to ‘38;5;255’ for 88-color and
256-color modes foreground colors, ‘49’ for default background color,
‘40’ to ‘47’ for background colors, ‘100’ to ‘107’ for 16-color mode
background colors, and ‘48;5;0’ to ‘48;5;255’ for 88-color and 256-color
modes background colors.
The two-letter names used in the ‘GREP_COLORS’ environment variable
(and some of the others) refer to terminal “capabilities,” the ability
of a terminal to highlight text, or change its color, and so on. These
capabilities are stored in an online database and accessed by the
‘terminfo’ library.
‘GREP_COLOR’
This variable specifies the color used to highlight matched
(non-empty) text. It is deprecated in favor of ‘GREP_COLORS’, but
still supported. The ‘mt’, ‘ms’, and ‘mc’ capabilities of
‘GREP_COLORS’ have priority over it. It can only specify the color
used to highlight the matching non-empty text in any matching line
(a selected line when the ‘-v’ command-line option is omitted, or a
context line when ‘-v’ is specified). The default is ‘01;31’,
which means a bold red foreground text on the terminal’s default
background.
‘GREP_COLORS’
This variable specifies the colors and other attributes used to
highlight various parts of the output. Its value is a
colon-separated list of ‘terminfo’ capabilities that defaults to
‘ms=01;31:mc=01;31:sl=:cx=:fn=35:ln=32:bn=32:se=36’ with the ‘rv’
and ‘ne’ boolean capabilities omitted (i.e., false). Supported
capabilities are as follows.
‘sl=’
SGR substring for whole selected lines (i.e., matching lines
when the ‘-v’ command-line option is omitted, or non-matching
lines when ‘-v’ is specified). If however the boolean ‘rv’
capability and the ‘-v’ command-line option are both
specified, it applies to context matching lines instead. The
default is empty (i.e., the terminal’s default color pair).
‘cx=’
SGR substring for whole context lines (i.e., non-matching
lines when the ‘-v’ command-line option is omitted, or
matching lines when ‘-v’ is specified). If however the
boolean ‘rv’ capability and the ‘-v’ command-line option are
both specified, it applies to selected non-matching lines
instead. The default is empty (i.e., the terminal’s default
color pair).
‘rv’
Boolean value that reverses (swaps) the meanings of the ‘sl=’
and ‘cx=’ capabilities when the ‘-v’ command-line option is
specified. The default is false (i.e., the capability is
omitted).
‘mt=01;31’
SGR substring for matching non-empty text in any matching line
(i.e., a selected line when the ‘-v’ command-line option is
omitted, or a context line when ‘-v’ is specified). Setting
this is equivalent to setting both ‘ms=’ and ‘mc=’ at once to
the same value. The default is a bold red text foreground
over the current line background.
‘ms=01;31’
SGR substring for matching non-empty text in a selected line.
(This is used only when the ‘-v’ command-line option is
omitted.) The effect of the ‘sl=’ (or ‘cx=’ if ‘rv’)
capability remains active when this takes effect. The default
is a bold red text foreground over the current line
background.
‘mc=01;31’
SGR substring for matching non-empty text in a context line.
(This is used only when the ‘-v’ command-line option is
specified.) The effect of the ‘cx=’ (or ‘sl=’ if ‘rv’)
capability remains active when this takes effect. The default
is a bold red text foreground over the current line
background.
‘fn=35’
SGR substring for file names prefixing any content line. The
default is a magenta text foreground over the terminal’s
default background.
‘ln=32’
SGR substring for line numbers prefixing any content line.
The default is a green text foreground over the terminal’s
default background.
‘bn=32’
SGR substring for byte offsets prefixing any content line.
The default is a green text foreground over the terminal’s
default background.
‘se=36’
SGR substring for separators that are inserted between
selected line fields (‘:’), between context line fields (‘-’),
and between groups of adjacent lines when nonzero context is
specified (‘--’). The default is a cyan text foreground over
the terminal’s default background.
‘ne’
Boolean value that prevents clearing to the end of line using
Erase in Line (EL) to Right (‘\33[K’) each time a colorized
item ends. This is needed on terminals on which EL is not
supported. It is otherwise useful on terminals for which the
‘back_color_erase’ (‘bce’) boolean ‘terminfo’ capability does
not apply, when the chosen highlight colors do not affect the
background, or when EL is too slow or causes too much flicker.
The default is false (i.e., the capability is omitted).
Note that boolean capabilities have no ‘=’... part. They are
omitted (i.e., false) by default and become true when specified.
‘LC_ALL’
‘LC_COLLATE’
‘LANG’
These variables specify the locale for the ‘LC_COLLATE’ category,
which might affect how range expressions like ‘[a-z]’ are
interpreted.
‘LC_ALL’
‘LC_CTYPE’
‘LANG’
These variables specify the locale for the ‘LC_CTYPE’ category,
which determines the type of characters, e.g., which characters are
whitespace. This category also determines the character encoding.
⇒Character Encoding.
‘LANGUAGE’
‘LC_ALL’
‘LC_MESSAGES’
‘LANG’
These variables specify the locale for the ‘LC_MESSAGES’ category,
which determines the language that ‘grep’ uses for messages. The
default ‘C’ locale uses American English messages.
‘POSIXLY_CORRECT’
If set, ‘grep’ behaves as POSIX requires; otherwise, ‘grep’ behaves
more like other GNU programs. POSIX requires that options that
follow file names must be treated as file names; by default, such
options are permuted to the front of the operand list and are
treated as options. Also, ‘POSIXLY_CORRECT’ disables special
handling of an invalid bracket expression. ⇒
invalid-bracket-expr.
‘_N_GNU_nonoption_argv_flags_’
(Here ‘N’ is ‘grep’’s numeric process ID.) If the Ith character of
this environment variable’s value is ‘1’, do not consider the Ith
operand of ‘grep’ to be an option, even if it appears to be one. A
shell can put this variable in the environment for each command it
runs, specifying which operands are the results of file name
wildcard expansion and therefore should not be treated as options.
This behavior is available only with the GNU C library, and only
when ‘POSIXLY_CORRECT’ is not set.
The ‘GREP_OPTIONS’ environment variable of ‘grep’ 2.20 and earlier is
no longer supported, as it caused problems when writing portable
scripts. To make arbitrary changes to how ‘grep’ works, you can use an
alias or script instead. For example, if ‘grep’ is in the directory
‘/usr/bin’ you can prepend ‘$HOME/bin’ to your ‘PATH’ and create an
executable script ‘$HOME/bin/grep’ containing the following:
#! /bin/sh
export PATH=/usr/bin
exec grep --color=auto --devices=skip "$@"
Info Catalog
grep: Command-line Options
grep: Invoking
grep: Exit Status