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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_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).

   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_OPTIONS'
     This variable specifies default options to be placed in front of
     any explicit options.  For example, if `GREP_OPTIONS' is
     `--binary-files=without-match --directories=skip', `grep' behaves
     as if the two options `--binary-files=without-match' and
     `--directories=skip' had been specified before any explicit
     options.  Option specifications are separated by whitespace.  A
     backslash escapes the next character, so it can be used to specify
     an option containing whitespace or a backslash.

     The `GREP_OPTIONS' value does not affect whether `grep' without
     file operands searches standard input or the working directory;
     that is affected only by command-line options.  For example, the
     command `grep PAT' searches standard input and the command `grep
     -r PAT' searches the working directory, regardless of whether
     `GREP_OPTIONS' contains `-r'.

`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 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.

`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.  Note:
     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.