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, 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_MESSAGES is set to
pt_BR, then the Brazilian Portuguese locale is used for 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.
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
Specifies the colors and other attributes used to
highlight various parts of the output. Its value is a
colon-separated list of 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 only used when the -v
command-line option is omitted.) The effect of the
sl= (or cx= if rv) capability remains active when
this kicks in. 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 only used when the -v
command-line option is specified.) The effect of
the cx= (or sl= if rv) capability remains active
when this kicks in. 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.
See the Select Graphic Rendition (SGR) section in the
documentation of the text terminal that is used for
permitted values and their meaning 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.
LC_ALL, LC_COLLATE, LANG
These variables specify the locale for the LC_COLLATE
category, which determines the collating sequence used to
interpret range expressions like [a-z].
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, that is, whether text
is encoded in UTF-8, ASCII, or some other encoding. In
the C or POSIX locale, all characters are encoded as a
single byte and every byte is a valid character.
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,
POSIX requires that unrecognized options be diagnosed as
'illegal', but since they are not really against the law
the default is to diagnose them as 'invalid'.
POSIXLY_CORRECT also disables
_N_GNU_nonoption_argv_flags_, described below.
_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.
