Provided by: grep_3.7-0ubuntu1_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  I<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.

       -l, --files-with-matches
              Suppress normal output; instead print the name of each input file from which output
              would normally have been printed.  Scanning each input file stops upon 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.  This is a GNU extension.

       -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.

       -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.

       --group-separator=SEP
              When -A, -B, or -C are in use, print SEP instead of -- between groups of lines.

       --no-group-separator
              When -A, -B, or -C are in use, do not print a separator between groups of lines.

   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,  B<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
       B<pcresyntax>(3) and B<pcrepattern>(3), but work only if PCRE support is enabled.

       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, 2005-2021 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.