grep(1)


NAME
     grep, egrep, fgrep - print lines matching a pattern

SYNOPOSIS
     grep [ -[[AB] ]num ] [ -[CEFGVBchilnsvwx] ] [ -e ] pattern | -ffile  ]  [
     files... ]

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.

     There are three major variants  of  grep,  controlled  by  the  following
     options.
     -G   Interpret pattern as a basic regular expression (see  below).   This
          is the default.
     -E   Interpret pattern as an extended regular expression (see below).
     -F   Interpret pattern as a list of fixed strings, separated by newlines,
          any of which is to be matched.
     In addition, two variant programs egrep and fgrep are  available.   Egrep
     is  similiar  (but  not identical) to grep -E, and is compatible with the
     historical Unix egrep.  Fgrep is the same as grep -F.

     All variants of grep understand the following options:
     -num Matches will be printed with  num  lines  of  leading  and  trailing
          context.   However,  grep  will never print any given line more than
          once.
     -A num
          Print num lines of trailing context after matching lines.
     -B num
          Print num lines of leading context before matching lines.
     -C   Equivalent to -2.
     -V   Print the version number of grep to standard  error.   This  version
          number should be included in all bug reports (see below).
     -b   Print the byte offset within the input  file  before  each  line  of
          output.
     -c   Suppress normal output; instead print a count of matching lines  for
          each input file.  With the -v option (see below), count non-matching
          lines.
     -e pattern
          Use pattern as the pattern; useful  to  protect  patterns  beginning
          with -.
     -f file
          Obtain the pattern from file.
     -h   Suppress the prefixing of filenames on output  when  multiple  files
          are searched.



     -i   Ignore case distinctions in both the pattern and the input files.
     -L   Suppress normal output; instead print the name of  each  input  file
          from which no output would normally have been printed.
     -l   Suppress normal output; instead print the name of  each  input  file
          from which output would normally have been printed.
     -n   Prefix each line of output with the line  number  within  its  input
          file.
     -q   Quiet; suppress normal output.
     -s   Suppress error messages about nonexistent or unreadable files.
     -v   Invert the sense of matching, to select non-matching lines.
     -w   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.
     -x   Select only those matches that exactly match the whole line.

REGULAR EXPRESSIONS

     A regular expression is a  pattern  that  describes  a  set  of  strings.
     Regular   expressions   are   constructed   analagously   to   arithmetic
     expressions, 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
     available 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 list of characters enclosed by [ and ] 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.   A range of ASCII
     characters may be specified by giving  the  first  and  last  characters,
     separated  by a hyphen.  Finally, certain named classes of characters are
     predefined.  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 is dependent upon
     the ASCII character encoding, whereas the former is portable.  (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 matching a single character 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 optional and is matched at most m 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
     subexpression.

     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 regular
     expression.

     In basic regular expressions the metacharacters ?, +, {, |, (, and ) lose
     their  special  meaning; instead use the backslashed versions \?, \+, \{,
     \|, \(, and \).

     In egrep the metacharacter { loses its special meaning; instead use \{.




DIAGNOSTICS

     Normally, exit status is 0 if matches were found, and  1  if  no  matches
     were  found.  (The -v option inverts the sense of the exit status.)  Exit
     status is 2 if there were syntax  errors  in  the  pattern,  inaccessible
     input files, or other system errors.

BUGS

     Email bug reports to bug-gnu-utils@prep.ai.mit.edu.  Be sure  to  include
     the word ``grep'' somewhere in the ``Subject:'' field.

     Large repetition counts in the {m,n} 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.