info grep

File: grep.info, Node: Environment Variables, Next: Exit Status, Prev: Command-line Options, Up: Invoking

2.2 Environment Variables
=========================

The behavior of ‘grep’ is affected by several environment variables, the
most important of which control the locale, which specifies how ‘grep’
interprets characters in its patterns and data.

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.UTF-8’, then a 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.

The following environment variables affect the behavior of ‘grep’.

‘GREP_COLOR’
This obsolescent variable interacts with ‘GREP_COLORS’ confusingly,
and ‘grep’ warns if it is set and is not overridden by
‘GREP_COLORS’. Instead of ‘GREP_COLOR='COLOR'’, you can use
‘GREP_COLORS='mt=COLOR'’.

‘GREP_COLORS’
This variable controls how the ‘--color’ option highlights 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).
The two-letter capability names 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. Non-empty capability values
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.

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.
*Note 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.

‘TERM’
This variable specifies the output terminal type, which can affect
what the ‘--color’ option does. *Note General Output Control::.

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 "$@"