grep command help

 grep, egrep, fgrep - print lines matching a pattern
 

SYNOPSIS

 grep [-[ABC] NUM] [-EFGHLUVZabchilnqrsuvwxyz] [-e PATTERN
 | -f FILE] [-d ACTION] [--directories=ACTION] [--extended-
 regexp] [--fixed-strings] [--basic-regexp] [--regexp=PATュ
 TERN] [--file=FILE] [--ignore-case] [--word-regexp]
 [--line-regexp] [--line-regexp] [--no-messages] [--invert-
 match] [--version] [--help] [--byte-offset] [--line-numュ
 ber] [--with-filename] [--no-filename] [--quiet]
 [--silent] [--text] [--files-without-match] [--files-with-
 matches] [--count] [--before-context=NUM] [--after-conュ
 text=NUM] [--context[=NUM]] [--binary] [--unix-byte-offュ
 sets] [--mmap] [--null] [--recursive] [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.
 
 There are three major variants of grep, controlled by the
 following options.
 -G, --basic-regexp
 Interpret pattern as a basic regular expression
 (see below). This is the default.
 -E, --extended-regexp
 Interpret pattern as an extended regular expression
 (see below).
 -F, --fixed-strings
 Interpret pattern as a list of fixed strings, sepaュ
 rated by newlines, any of which is to be matched.
 In addition, two variant programs egrep and fgrep are
 available. Egrep is the same as grep -E. Fgrep is the
 same as grep -F.
 
 All variants of grep understand the following options:
 -A NUM, --after-context=NUM
 Print NUM lines of trailing context after matching
 lines.
 -B NUM, --before-context=NUM
 Print NUM lines of leading context before matching
 lines.
 -C [NUM], --context[=NUM]
 Print NUM lines (default 2) of output context.
 -NUM Same as --context=NUM lines of leading and trailing
 context. However, grep will never print any given
 line more than once.
 -V, --version
 Print the version number of grep to standard error.
 This version number should be included in all bug
 reports (see below).
 Print the byte offset within the input file before
 each line of output.
 -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-matchュ
 ing lines.
 -d ACTION, --directories=ACTION
 If an input file is a directory, use ACTION to proュ
 cess it. By default, ACTION is read, which means
 that directories are read just as if they were
 ordinary files. If ACTION is skip, directories are
 silently skipped. If ACTION is recurse, grep reads
 all files under each directory, recursively; this
 is equivalent to the -r option.
 -e PATTERN, --regexp=PATTERN
 Use PATTERN as the pattern; useful to protect patュ
 terns beginning with -.
 -f FILE, --file=FILE
 Obtain patterns from FILE, one per line. The empty
 file contains zero patterns, and therfore matches
 nothing.
 -H, --with-filename
 Print the filename for each match.
 -h, --no-filename
 Suppress the prefixing of filenames on output when
 multiple files are searched.
 -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.
 -n, --line-number
 Prefix each line of output with the line number
 within its input file.
 -q, --quiet, --silent
 Quiet; suppress normal output. The scanning will
 stop on the first match. Also see the -s or --no-
 messages option below.
 -r, --recursive
 Read all files under each directory, recursively;
 this is equivalent to the -d recurse option.
 -s, --no-messages
 Suppress error messages about nonexistent or
 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.
 -a, --text
 Do not suppress output lines that contain binary
 data. Normally, if the first few bytes of a file
 indicate that the file contains binary data, grep
 outputs only a message saying that the file matches
 the pattern. This option causes grep to act as if
 the file is a text file, even if it would otherwise
 be treated as binary.
 -v, --invert-match
 Invert the sense of matching, to select non-matchュ
 ing 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 characュ
 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ュ
 ters, digits, and the underscore.
 -x, --line-regexp
 Select only those matches that exactly match the
 whole line.
 -y Obsolete synonym for -i.
 -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-Windows.
 -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 platforms other than MS-DOS and MS-Winュ
 dows.
 In some situations, --mmap yields better perforュ
 mance. However, --mmap can cause undefined behavュ
 ior (including core dumps) if an input file shrinks
 while grep is operating, or if an I/O error occurs.
 -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 newュ
 line. 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 expressions, by using various operators to
 combine smaller expressions.
 
 Grep understands two different versions of regular expresュ
 sion syntax: "basic" and "extended." In GNU grep, there
 is no difference in available functionality using either
 syntax. In other implementations, basic regular expresュ
 sions 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ュ
 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ュ
 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
 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
 first in the list. Similarly, to include a literal ^
 place it anywhere but first. Finally, to include a litュ
 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 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.
 {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ュ
 nating two substrings that respectively match the concateュ
 nated subexpressions.
 
 Two regular expressions may be joined by the infix operaュ
 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ュ
 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
 subexpression of the regular 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
 [{] to match a literal {.
 
 GNU egrep attempts to support traditional usage by assumュ
 ing that { is not special if it would be the start of an
 invalid interval specification. 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.
 

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ュ
 tax errors in the pattern, inaccessible input files, or
 other system errors.
 

BUGS

 Email bug reports to bug-gnu-utils@gnu.org. 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.