Provided by: grep_3.6-1_amd64 bug

NAME

       grep, egrep, fgrep, rgrep - print lines that match patterns

SYNOPSIS

       grep [OPTION...] PATTERNS [FILE...]
       grep [OPTION...] -e PATTERNS ... [FILE...]
       grep [OPTION...] -f PATTERN_FILE ... [FILE...]

DESCRIPTION

       grep  searches  for  PATTERNS in each FILE.  PATTERNS is one or more patterns separated by
       newline characters, and grep prints each line that matches a pattern.  Typically  PATTERNS
       should be quoted when grep is used in a shell command.

       A  FILE of “-” stands for standard input.  If no FILE is given, recursive searches examine
       the working directory, and nonrecursive searches read standard input.

       In addition, the variant programs egrep, fgrep and rgrep are the same as grep -E, grep -F,
       and  grep -r,  respectively.  These variants are deprecated, but are provided for backward
       compatibility.

OPTIONS

   Generic Program Information
       --help Output a usage message and exit.

       -V, --version
              Output the version number of grep and exit.

   Pattern Syntax
       -E, --extended-regexp
              Interpret PATTERNS as extended regular expressions (EREs, see below).

       -F, --fixed-strings
              Interpret PATTERNS as fixed strings, not regular expressions.

       -G, --basic-regexp
              Interpret PATTERNS as basic regular expressions (BREs, see  below).   This  is  the
              default.

       -P, --perl-regexp
              Interpret  PATTERNS as Perl-compatible regular expressions (PCREs).  This option is
              experimental when combined with the -z (--null-data) option, and grep -P  may  warn
              of unimplemented features.

   Matching Control
       -e PATTERNS, --regexp=PATTERNS
              Use PATTERNS as the patterns.  If this option is used multiple times or is combined
              with the -f (--file) option, search for all patterns given.   This  option  can  be
              used to protect a pattern beginning with “-”.

       -f FILE, --file=FILE
              Obtain  patterns from FILE, one per line.  If this option is used multiple times or
              is combined with the -e (--regexp) option, search  for  all  patterns  given.   The
              empty file contains zero patterns, and therefore matches nothing.

       -i, --ignore-case
              Ignore case distinctions in patterns and input data, so that characters that differ
              only in case match each other.

       --no-ignore-case
              Do not ignore case distinctions in patterns and input data.  This is  the  default.
              This  option  is useful for passing to shell scripts that already use -i, to cancel
              its effects because the two options override each other.

       -v, --invert-match
              Invert the sense of matching, to select non-matching lines.

       -w, --word-regexp
              Select only those lines containing matches that form whole words.  The test is that
              the  matching substring must either be at the beginning of the line, or preceded by
              a non-word constituent character.  Similarly, it must be either at the end  of  the
              line  or followed by a non-word constituent character.  Word-constituent characters
              are letters, digits, and the underscore.  This option has no effect if -x  is  also
              specified.

       -x, --line-regexp
              Select  only  those  matches  that  exactly  match  the  whole line.  For a regular
              expression pattern, this is like parenthesizing the pattern and then surrounding it
              with ^ and $.

       -y     Obsolete synonym for -i.

   General Output Control
       -c, --count
              Suppress  normal  output;  instead  print  a count of matching lines for each input
              file.  With the -v, --invert-match option (see below), count non-matching lines.

       --color[=WHEN], --colour[=WHEN]
              Surround the matched (non-empty)  strings,  matching  lines,  context  lines,  file
              names, line numbers, byte offsets, and separators (for fields and groups of context
              lines) with escape sequences to display them in color on the terminal.  The  colors
              are  defined  by  the environment variable GREP_COLORS.  The deprecated environment
              variable GREP_COLOR is still supported, but its setting  does  not  have  priority.
              WHEN is never, always, or auto.

       -L, --files-without-match
              Suppress  normal  output;  instead  print the name of each input file from which no
              output would normally have been printed.  The  scanning  will  stop  on  the  first
              match.

       -l, --files-with-matches
              Suppress normal output; instead print the name of each input file from which output
              would normally have been printed.  The scanning will stop on the first match.

       -m NUM, --max-count=NUM
              Stop reading a file after NUM matching lines.  If the input is standard input  from
              a  regular  file, and NUM matching lines are output, grep ensures that the standard
              input is positioned to just after the last matching line before exiting, regardless
              of  the  presence  of  trailing  context  lines.  This enables a calling process to
              resume a search.  When grep stops after NUM matching lines, it outputs any trailing
              context  lines.  When the -c or --count option is also used, grep does not output a
              count greater than NUM.  When the -v or --invert-match option is  also  used,  grep
              stops after outputting NUM non-matching lines.

       -o, --only-matching
              Print only the matched (non-empty) parts of a matching line, with each such part on
              a separate output line.

       -q, --quiet, --silent
              Quiet; do not write anything to standard output.  Exit immediately with zero status
              if  any  match  is  found,  even  if  an  error  was  detected.  Also see the -s or
              --no-messages option.

       -s, --no-messages
              Suppress error messages about nonexistent or unreadable files.

   Output Line Prefix Control
       -b, --byte-offset
              Print the 0-based byte offset within the input file before each line of output.  If
              -o (--only-matching) is specified, print the offset of the matching part itself.

       -H, --with-filename
              Print  the  file  name for each match.  This is the default when there is more than
              one file to search.

       -h, --no-filename
              Suppress the prefixing of file names on output.  This is the default when there  is
              only one file (or only standard input) to search.

       --label=LABEL
              Display  input actually coming from standard input as input coming from file LABEL.
              This can be useful for commands that transform a file's contents before  searching,
              e.g.,  gzip  -cd  foo.gz  |  grep  --label=foo  -H 'some pattern'.  See also the -H
              option.

       -n, --line-number
              Prefix each line of output with the 1-based line number within its input file.

       -T, --initial-tab
              Make sure that the first character of actual line content lies on a  tab  stop,  so
              that  the  alignment of tabs looks normal.  This is useful with options that prefix
              their output to the actual content:  -H,-n,  and  -b.   In  order  to  improve  the
              probability  that  lines from a single file will all start at the same column, this
              also causes the line number and byte offset (if present) to be printed in a minimum
              size field width.

       -u, --unix-byte-offsets
              Report  Unix-style byte offsets.  This switch causes grep to report byte offsets as
              if the file were a Unix-style text file, i.e., with  CR  characters  stripped  off.
              This will produce results identical to running grep on a Unix machine.  This option
              has no effect unless -b option is also used; it has no effect  on  platforms  other
              than MS-DOS and MS-Windows.

       -Z, --null
              Output a zero byte (the ASCII NUL character) instead of the character that normally
              follows a file name.  For example, grep -lZ outputs a zero  byte  after  each  file
              name  instead of the usual newline.  This option makes the output unambiguous, even
              in the presence of file names containing unusual characters  like  newlines.   This
              option  can be used with commands like find -print0, perl -0, sort -z, and xargs -0
              to process arbitrary file names, even those that contain newline characters.

   Context Line Control
       -A NUM, --after-context=NUM
              Print NUM lines of trailing context after matching lines.  Places a line containing
              a  group  separator  (--)  between  contiguous  groups  of matches.  With the -o or
              --only-matching option, this has no effect and a warning is given.

       -B NUM, --before-context=NUM
              Print NUM lines of leading context before matching lines.  Places a line containing
              a  group  separator  (--)  between  contiguous  groups  of matches.  With the -o or
              --only-matching option, this has no effect and a warning is given.

       -C NUM, -NUM, --context=NUM
              Print NUM lines of output context.  Places a line containing a group separator (--)
              between  contiguous groups of matches.  With the -o or --only-matching option, this
              has no effect and a warning is given.

   File and Directory Selection
       -a, --text
              Process  a  binary  file  as  if  it  were  text;  this  is   equivalent   to   the
              --binary-files=text option.

       --binary-files=TYPE
              If  a  file's  data or metadata indicate that the file contains binary data, assume
              that the file is of type TYPE.  Non-text bytes  indicate  binary  data;  these  are
              either  output  bytes  that  are improperly encoded for the current locale, or null
              input bytes when the -z option is not given.

              By default, TYPE is binary, and grep suppresses output after null input binary data
              is  discovered,  and  suppresses output lines that contain improperly encoded data.
              When some output is suppressed, grep follows any output  with  a  one-line  message
              saying that a binary file matches.

              If  TYPE  is  without-match,  when grep discovers null input binary data it assumes
              that the rest of the file does not match; this is equivalent to the -I option.

              If TYPE is text, grep processes  a  binary  file  as  if  it  were  text;  this  is
              equivalent to the -a option.

              When type is binary, grep may treat non-text bytes as line terminators even without
              the -z option.  This means choosing binary versus text can affect whether a pattern
              matches  a  file.   For  example,  when type is binary the pattern q$ might match q
              immediately followed by a null byte, even though this is not matched when  type  is
              text.   Conversely,  when  type  is binary the pattern . (period) might not match a
              null byte.

              Warning: The -a option might output binary  garbage,  which  can  have  nasty  side
              effects  if  the output is a terminal and if the terminal driver interprets some of
              it as commands.  On the other hand, when reading files  whose  text  encodings  are
              unknown,  it  can  be helpful to use -a or to set LC_ALL='C' in the environment, in
              order to find more matches even if the matches are unsafe for direct display.

       -D ACTION, --devices=ACTION
              If an input file is a device, FIFO  or  socket,  use  ACTION  to  process  it.   By
              default,  ACTION  is  read,  which means that devices are read just as if they were
              ordinary files.  If ACTION is skip, devices are silently skipped.

       -d ACTION, --directories=ACTION
              If an input file is a directory, use ACTION to process it.  By default,  ACTION  is
              read,  i.e.,  read  directories  just as if they were ordinary files.  If ACTION is
              skip, silently skip directories.  If ACTION is recurse, read all files  under  each
              directory,  recursively,  following  symbolic links only if they are on the command
              line.  This is equivalent to the -r option.

       --exclude=GLOB
              Skip any command-line file with a name suffix that matches the pattern GLOB,  using
              wildcard  matching; a name suffix is either the whole name, or a trailing part that
              starts with a non-slash character immediately after a slash (/) in the name.   When
              searching recursively, skip any subfile whose base name matches GLOB; the base name
              is the part after the last slash.  A pattern can use *, ?, and [...] as  wildcards,
              and \ to quote a wildcard or backslash character literally.

       --exclude-from=FILE
              Skip files whose base name matches any of the file-name globs read from FILE (using
              wildcard matching as described under --exclude).

       --exclude-dir=GLOB
              Skip any command-line directory with a name suffix that matches the  pattern  GLOB.
              When  searching  recursively,  skip  any subdirectory whose base name matches GLOB.
              Ignore any redundant trailing slashes in GLOB.

       -I     Process a binary file as if it did not contain matching data; this is equivalent to
              the --binary-files=without-match option.

       --include=GLOB
              Search  only  files  whose  base  name  matches  GLOB  (using  wildcard matching as
              described under --exclude).  If contradictory --include and --exclude  options  are
              given,  the  last matching one wins.  If no --include or --exclude options match, a
              file is included unless the first such option is --include.

       -r, --recursive
              Read all files under each directory, recursively, following symbolic links only  if
              they are on the command line.  Note that if no file operand is given, grep searches
              the working directory.  This is equivalent to the -d recurse option.

       -R, --dereference-recursive
              Read all files under each  directory,  recursively.   Follow  all  symbolic  links,
              unlike -r.

   Other Options
       --line-buffered
              Use line buffering on output.  This can cause a performance penalty.

       -U, --binary
              Treat the file(s) as binary.  By default, under MS-DOS and MS-Windows, grep guesses
              whether a file is text or binary as described for the  --binary-files  option.   If
              grep decides the file is a text file, it strips the CR characters from the original
              file  contents  (to  make  regular  expressions  with  ^  and  $  work  correctly).
              Specifying  -U overrules this guesswork, causing all files to be read and passed to
              the matching mechanism verbatim; if the file is a text file with CR/LF pairs at the
              end  of  each  line, this will cause some regular expressions to fail.  This option
              has no effect on platforms other than MS-DOS and MS-Windows.

       -z, --null-data
              Treat input and output data as sequences of lines, each terminated by a  zero  byte
              (the ASCII NUL character) instead of a newline.  Like the -Z or --null option, this
              option can be used with commands like sort -z to process arbitrary file names.

REGULAR EXPRESSIONS

       A regular expression is a pattern that describes a set of  strings.   Regular  expressions
       are  constructed  analogously  to  arithmetic  expressions,  by using various operators to
       combine smaller expressions.

       grep understands three different versions of regular  expression  syntax:  “basic”  (BRE),
       “extended”  (ERE)  and  “perl”  (PCRE).   In  GNU grep there is no difference in available
       functionality between basic  and  extended  syntaxes.   In  other  implementations,  basic
       regular  expressions  are  less  powerful.   The following description applies to extended
       regular expressions; differences for basic regular expressions are summarized  afterwards.
       Perl-compatible  regular  expressions give additional functionality, and are documented in
       pcresyntax(3) and pcrepattern(3), but work only if PCRE is available in the system.

       The fundamental building blocks are the regular expressions that match a single character.
       Most  characters,  including  all  letters  and digits, are regular expressions that match
       themselves.  Any meta-character with special meaning may be quoted by preceding it with  a
       backslash.

       The  period  .  matches  any  single  character.   It is unspecified whether it matches an
       encoding error.

   Character Classes and Bracket Expressions
       A bracket expression is a list of characters enclosed by [ and ].  It matches  any  single
       character in that list.  If the first character of the list is the caret ^ then it matches
       any character not in the list; it is unspecified whether it  matches  an  encoding  error.
       For example, the regular expression [0123456789] matches any single digit.

       Within  a bracket expression, a range expression consists of two characters separated by a
       hyphen.  It matches any single character that sorts between the two characters, inclusive,
       using  the  locale's  collating sequence and character set.  For example, in the default C
       locale, [a-d] is equivalent to [abcd].  Many locales sort characters in dictionary  order,
       and  in  these locales [a-d] is typically not equivalent to [abcd]; it might be equivalent
       to  [aBbCcDd],  for  example.   To  obtain  the  traditional  interpretation  of   bracket
       expressions,  you  can  use the C locale by setting the LC_ALL environment variable to the
       value C.

       Finally, certain named classes of characters are predefined within bracket expressions, as
       follows.   Their names are self explanatory, and they are [:alnum:], [:alpha:], [:blank:],
       [:cntrl:], [:digit:], [:graph:], [:lower:], [:print:],  [:punct:],  [:space:],  [:upper:],
       and [:xdigit:].  For example, [[:alnum:]] means the character class of numbers and letters
       in the current locale.  In the C locale and ASCII character set encoding, this is the same
       as  [0-9A-Za-z].   (Note  that  the brackets in these class names are part of the symbolic
       names,  and  must  be  included  in  addition  to  the  brackets  delimiting  the  bracket
       expression.)   Most meta-characters lose their special meaning inside bracket expressions.
       To include a literal ] place it first in the list.  Similarly,  to  include  a  literal  ^
       place it anywhere but first.  Finally, to include a literal - place it last.

   Anchoring
       The  caret  ^  and the dollar sign $ are meta-characters that respectively match the empty
       string at the beginning and end of a line.

   The Backslash Character and Special Expressions
       The symbols \< and \> respectively match the empty string at the beginning and  end  of  a
       word.   The  symbol  \b matches the empty string at the edge of a word, and \B matches the
       empty string provided it's not at the edge of a word.  The symbol  \w  is  a  synonym  for
       [_[:alnum:]] and \W is a synonym for [^_[:alnum:]].

   Repetition
       A regular expression may be followed by one of several repetition operators:
       ?      The preceding item is optional and matched at most once.
       *      The preceding item will be matched zero or more times.
       +      The preceding item will be matched one or more times.
       {n}    The preceding item is matched exactly n times.
       {n,}   The preceding item is matched n or more times.
       {,m}   The preceding item is matched at most m times.  This is a GNU extension.
       {n,m}  The preceding item is matched at least n times, but not more than m times.

   Concatenation
       Two  regular expressions may be concatenated; the resulting regular expression matches any
       string formed by concatenating two substrings that  respectively  match  the  concatenated
       expressions.

   Alternation
       Two  regular  expressions  may  be  joined  by the infix operator |; the resulting regular
       expression matches any string matching either alternate expression.

   Precedence
       Repetition takes precedence over  concatenation,  which  in  turn  takes  precedence  over
       alternation.   A  whole  expression  may  be  enclosed  in  parentheses  to override these
       precedence rules and form a subexpression.

   Back-references and Subexpressions
       The back-reference \n, where n is a single digit, matches the substring previously matched
       by the nth parenthesized subexpression of the regular expression.

   Basic vs Extended Regular Expressions
       In  basic  regular expressions the meta-characters ?, +, {, |, (, and ) lose their special
       meaning; instead use the backslashed versions \?, \+, \{, \|, \(, and \).

EXIT STATUS

       Normally the exit status is 0 if a line is selected, 1 if no lines were selected, and 2 if
       an  error  occurred.   However,  if  the  -q  or --quiet or --silent is used and a line is
       selected, the exit status is 0 even if an error occurred.

ENVIRONMENT

       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.

NOTES

       This man page is maintained only fitfully; the full documentation  is  often  more  up-to-
       date.

COPYRIGHT

       Copyright 1998-2000, 2002, 2005-2020 Free Software Foundation, Inc.

       This  is  free software; see the source for copying conditions.  There is NO warranty; not
       even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

BUGS

   Reporting Bugs
       Email bug reports to the  bug-reporting  address  ⟨bug-grep@gnu.org⟩.   An  email  archive
       ⟨https://lists.gnu.org/mailman/listinfo/bug-grep⟩       and       a       bug      tracker
       ⟨https://debbugs.gnu.org/cgi/pkgreport.cgi?package=grep⟩ are available.

   Known Bugs
       Large repetition counts in the {n,m} construct may cause grep to use lots of  memory.   In
       addition,  certain  other  obscure regular expressions require exponential time and space,
       and may cause grep to run out of memory.

       Back-references are very slow, and may require exponential time.

EXAMPLE

       The following example outputs the location and contents of any  line  containing  “f”  and
       ending  in “.c”, within all files in the current directory whose names contain “g” and end
       in “.h”.  The -n option outputs line numbers, the -- argument treats expansions of “*g*.h”
       starting  with  “-”  as  file  names not options, and the empty file /dev/null causes file
       names to be output even if only one file name happens to be of the form “*g*.h”.

         $ grep -n -- 'f.*\.c$' *g*.h /dev/null
         argmatch.h:1:/* definitions and prototypes for argmatch.c

       The only line that matches is line 1 of argmatch.h.   Note  that  the  regular  expression
       syntax  used  in the pattern differs from the globbing syntax that the shell uses to match
       file names.

SEE ALSO

   Regular Manual Pages
       awk(1), cmp(1), diff(1), find(1), perl(1), sed(1), sort(1),  xargs(1),  read(2),  pcre(3),
       pcresyntax(3), pcrepattern(3), terminfo(5), glob(7), regex(7).

   Full Documentation
       A  complete  manual ⟨https://www.gnu.org/software/grep/manual/⟩ is available.  If the info
       and grep programs are properly installed at your site, the command

              info grep

       should give you access to the complete manual.