Ubuntu Manpage: grep, egrep, fgrep, rgrep - print lines that match patterns

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.