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How to use the grep command

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grep


     grep, egrep, fgrep - print lines matching a pattern

SYNOPSIS

      grep [options] PATTERN [FILE...]
      grep [options] [-e PATTERN | -f FILE] [FILE...]

DESCRIPTION

      Grep  searches the named input FILEs (or standard input if no files are
      named, or the file name - is given) for lines containing a match to the
      given PATTERN.  By default, grep prints the matching lines.
      In addition, two variant programs egrep and fgrep are available.  Egrep
      is the same as grep -E.  Fgrep is the same as grep -F.

OPTIONS

      -A NUM, --after-context=NUM
             Print NUM  lines  of  trailing  context  after  matching  lines.
             Places  a  line  containing—between  contiguous  groups  of
             matches.
      -a, --text
             Process a binary file as if it were text; this is equivalent  to
             the—binary-files=text option.
      -B NUM, --before-context=NUM
             Print  NUM  lines  of  leading  context  before  matching lines.
             Places  a  line  containing—between  contiguous  groups  of
             matches.
      -C NUM, --context=NUM
             Print  NUM lines of output context.  Places a line containing—between contiguous groups of matches.
      -b, --byte-offset
             Print the byte offset within the input file before each line  of
             output.
      --binary-files=TYPE
             If the first few bytes of a file indicate that the file contains
             binary data, assume that the file is of type TYPE.  By  default,
             TYPE is binary, and grep normally outputs either a one-line mes-
             sage saying that a binary file matches, or no message  if  there
             is  no  match.   If  TYPE  is without-match, grep assumes that a
             binary 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.   Warning:  grep—binary-files=text  might output binary garbage, which can have
             nasty side effects if the output is a terminal and if the termi-
             nal driver interprets some of it as commands.
      --colour[=WHEN], --color[=WHEN]
             Surround  the matching string with the marker find in GREP_COLOR
             environment variable. WHEN may be `never', `always', or `auto'
      -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.
      -D ACTION, --devices=ACTION
             If an input file is a device, FIFO or socket, use ACTION to pro-
             cess  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, which means that directories  are  read
             just  as if they were ordinary files.  If ACTION is skip, direc-
             tories are silently skipped.  If ACTION is recurse,  grep  reads
             all  files under each directory, recursively; this is equivalent
             to the -r option.
      -E, --extended-regexp
             Interpret PATTERN as an extended regular expression (see below).
      -e PATTERN, --regexp=PATTERN
             Use PATTERN as the pattern; useful to protect patterns beginning
             with -.
      -F, --fixed-strings
             Interpret PATTERN as a list of fixed strings, separated by  new-
             lines,  any of which is to be matched.  -P, --perl-regexp Inter-
             pret PATTERN as a Perl regular expression.
      -f FILE, --file=FILE
             Obtain patterns from FILE, one per line.  The  empty  file  con-
             tains zero patterns, and therefore matches nothing.
      -G, --basic-regexp
             Interpret  PATTERN  as  a  basic regular expression (see below).
             This is the default.
      -H, --with-filename
             Print the filename for each match.
      -h, --no-filename
             Suppress the prefixing of  filenames  on  output  when  multiple
             files are searched.
      --help Output a brief help message.
      -I     Process  a  binary  file as if it did not contain matching data;
             this is equivalent to the—binary-files=without-match option.
      -i, --ignore-case
             Ignore case distinctions in  both  the  PATTERN  and  the  input
             files.
      -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.
      --mmap If possible, use the mmap(2) system call to read input,  instead
             of  the default read(2) system call.  In some situations, --mmap
             yields better performance.  However, --mmap can cause  undefined
             behavior  (including  core dumps) if an input file shrinks while
             grep is operating, or if an I/O error occurs.
      -n, --line-number
             Prefix each line of output with the line number within its input
             file.
      -o, --only-matching
             Show only the part of a matching line that matches PATTERN.
      --label=LABEL
             Displays input actually coming from standard input as input com-
             ing from file LABEL.  This is especially useful for  tools  like
             zgrep, e.g.  gzip -cd foo.gz |grep—label=foo something—line-buffering
             Use line buffering, it can be a performance penalty.
      -q, --quiet, --silent
             Quiet;  do  not write anything to standard output.  Exit immedi-
             ately with zero status if any match is found, even if  an  error
             was detected.  Also see the -s or—no-messages option.
      -R, -r, --recursive
             Read all files under each directory, recursively; this is equiv-
             alent to the -d recurse option.
        --include=PATTERN
             Recurse in directories only searching file matching PATTERN.
        --exclude=PATTERN
             Recurse in directories skip file matching PATTERN.
      -s, --no-messages
             Suppress error messages about nonexistent or  unreadable  files.
             Portability note: unlike GNU grep, traditional grep did not con-
             form to POSIX.2, because traditional grep lacked a -q option and
             its  -s option behaved like GNU grep's -q option.  Shell scripts
             intended to be portable to traditional grep should avoid both -q
             and -s and should redirect output to /dev/null instead.
      -U, --binary
             Treat  the  file(s) as binary.  By default, under MS-DOS and MS-Windows,
grep guesses the file type by looking at  the  contents
             of  the first 32KB read from the file.  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-Win-
             dows.
      -u, --unix-byte-offsets
             Report  Unix-style  byte  offsets.   This  switch causes grep to
             report byte offsets as if the file were  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 plat-
             forms other than MS-DOS and MS-Windows.
      -V, --version
             Print the version number of grep to standard error.   This  ver-
             sion number should be included in all bug reports (see below).
      -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 con-
             stituent 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.
      -x, --line-regexp
             Select only those matches that exactly match the whole line.
      -y     Obsolete synonym for -i.
      -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.

REGULAR EXPRESSIONS

      A regular expression is a pattern that  describes  a  set  of  strings.
      Regular  expressions  are constructed analogously to arithmetic express-
      sions, by using various operators to combine smaller expressions.
      Grep understands two different versions of regular  expression  syntax:
      "basic"  and "extended."  In GNU grep, there is no difference in avail-
      able functionality using  either  syntax.   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.
      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 metacharacter with
      special meaning may be quoted by preceding it with a backslash.
      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.
      For  example,  the  regular  expression [0123456789] matches any single
      digit.
      Within a bracket expression, a range expression consists of two charac-
      ters 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 dictio-
      nary  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:],  [:cntrl:],   [:digit:],   [:graph:],
      [:lower:],  [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:].
      For example, alnum: means  [0-9A-Za-z],  except  the  latter  form
      depends upon the C locale and the ASCII character encoding, whereas the
      former is independent of locale and  character  set.   (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  list.)
      Most  metacharacters  lose  their  special  meaning  inside  lists.  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.
      The period .  matches any single character.  The symbol \w is a synonym
      for alnum: and \W is a synonym for [^[:alnum]].
      The  caret ^ and the dollar sign $ are metacharacters that respectively
      match the empty string at the beginning and end of a line.  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.
      A regular expression may be followed by one of several repetition oper-
      ators:
      ?      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.
      {n,m}  The  preceding  item  is  matched at least n times, but not more
             than m times.
      Two regular expressions may  be  concatenated;  the  resulting  regular
      expression  matches  any  string formed by concatenating two substrings
      that respectively match the concatenated subexpressions.
      Two regular expressions may be joined by  the  infix  operator  |;  the
      resulting  regular expression matches any string matching either subex-
      pression.
      Repetition takes precedence over concatenation,  which  in  turn  takes
      precedence  over alternation.  A whole subexpression may be enclosed in
      parentheses to override these precedence rules.
      The backreference \n, where n is a single digit, matches the  substring
      previously  matched by the nth parenthesized subexpression of the regu-
      lar expression.
      In basic regular expressions the metacharacters ?, +, {, |,  (,  and  )
      lose  their  special  meaning; instead use the backslashed versions \?,
      \+, \{, \|, \(, and \).
      Traditional egrep did not support the { metacharacter, and  some  egrep
      implementations  support \{ instead, so portable scripts should avoid {
      in egrep patterns and should use [{] to match a literal {.
      GNU egrep attempts to support traditional usage by assuming that  {  is
      not  special if it would be the start of an invalid interval specifica-
      tion.  For example, the shell command egrep '{1' searches for the  two-
      character  string {1 instead of reporting a syntax error in the regular
      expression.  POSIX.2 allows this behavior as an extension, but portable
      scripts should avoid it.

ENVIRONMENT VARIABLES

      Grep's behavior is affected by the following environment variables.
      A  locale  LC_foo is specified by examining the three environment vari-
      ables LC_ALL, LC_foo, LANG, in that order.  The first  of  these  vari-
      ables  that is set specifies the locale.  For example, if LC_ALL is not
      set, but LC_MESSAGES is set to pt_BR, then Brazilian Portuguese is used
      for  the  LC_MESSAGES  locale.   The  C locale is used if none of these
      environment variables  are  set,  or  if  the  locale  catalog  is  not
      installed,  or  if grep was not compiled with national language support
      (NLS).
      GREP_OPTIONS
             This variable specifies default options to be placed in front of
             any   explicit   options.    For  example,  if  GREP_OPTIONS  is
             '--binary-files=without-match—directories=skip', grep  behaves
             as  if the two options—binary-files=without-match and—direc-
             tories=skip had been  specified  before  any  explicit  options.
             Option  specifications are separated by whitespace.  A backslash
             escapes the next character, so it can  be  used  to  specify  an
             option containing whitespace or a backslash.
      GREP_COLOR
             Specifies the marker for highlighting.
      LC_ALL, LC_COLLATE, LANG
             These  variables specify the LC_COLLATE locale, which determines
             tories=skip had been  specified  before  any  explicit  options.
             Option  specifications are separated by whitespace.  A backslash
             escapes the next character, so it can  be  used  to  specify  an
             option containing whitespace or a backslash.
      GREP_COLOR
             Specifies the marker for highlighting.
      LC_ALL, LC_COLLATE, LANG
             These  variables specify the LC_COLLATE locale, which determines
             the collating sequence used to interpret range expressions  like
             [a-z].
      LC_ALL, LC_CTYPE, LANG
             These  variables  specify  the LC_CTYPE locale, which determines
             the type of characters, e.g., which characters are whitespace.
      LC_ALL, LC_MESSAGES, LANG
             These variables specify the LC_MESSAGES locale, 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.2  requires;  otherwise,  grep
             behaves  more  like  other  GNU programs.  POSIX.2 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.2  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_nonop-
             tion_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 com-
             mand 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.

DIAGNOSTICS

      Normally, exit status is 0 if selected lines are found and 1 otherwise.
      But the exit status is 2 if an error occurred, unless the -q or—quiet
      or—silent option is used and a selected line is found.

BUGS

      Email bug reports to bug-grep@gnu.org.
      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.
      Backreferences are very slow, and may require exponential time.
|}


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