GREP(1)                                                   GREP(1)


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



SYNOPSIS
       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, sepa-
              rated 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 pat-
              terns 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



GNU Project             1992 September 10                       1





GREP(1)                                                   GREP(1)


              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.
       -o     Always print filenames with output lines.
       -q     Quiet; suppress normal output.
       -s     Suppress   error   messages  about  nonexistent  or
              unreadable files.
       -v     "Versus" mode. 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 charac-
              ter.   Similarly,  it  must be either at the end of
              the line or  followed  by  a  non-word  constituent
              character.   Word-constituent  characters  are let-
              ters, 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 expres-
       sion  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  expres-
       sions  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  sin-
       gle  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



GNU Project             1992 September 10                       2





GREP(1)                                                   GREP(1)


       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 lit-
       eral - 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 concate-
       nating two substrings that respectively match the concate-
       nated subexpressions.

       Two  regular expressions may be joined by the infix opera-
       tor |; the resulting regular expression matches any string
       matching either subexpression.

       Repetition  takes  precedence over concatenation, which in
       turn takes precedence over alternation.   A  whole  subex-
       pression  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



GNU Project             1992 September 10                       3





GREP(1)                                                   GREP(1)


       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 syn-
       tax 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  ``Sub-
       ject:'' 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.

       Files  which  have  extremely long sequences of characters
       without newlines may cause grep to run out of memory.   An
       example  is  sparse  files,  which can read as arbritarily
       long sequences of nul characters.
























GNU Project             1992 September 10                       4