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Manual page for grep

Here is the UNIX manual page for the grep command as it would appear on a Linux machine:

GREP(1)                              GREP(1)

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

SYNOPSIS
   grep  [-[AB] NUM] [-CEFGVbchiLlnqsvwxyUu] 
   [-e PATTERN | -f FILE] [--extended-regexp]
   [--fixed-strings]  [--basic-reg-exp]   
   [--regexp=PATTERN]  [--file=FILE]  
   [--ignore-case] [--word-regexp] [--line-regexp]
   [--line-regexp] [--no-messages] [--revert-match]
   [--version] [--help] [--byte-offset]  
   [--line-number]  [--with-filename]  
   [--no-filename] [--quiet]  [--silent]
   [--files-without-match] [--files-with-matches] 
   [--count] [--before-context=NUM] [--after-
   context=NUM] [--context] [--binary] 
   [--unix-byte-offsets]  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, --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, separated by newlines, any of 
         which is to be matched.
     
   In  addition, two variant programs egrep and 
   fgrep are available. Egrep is similar (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, --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, --context
         Equivalent to -2.
   -V, --version
         Print the version number of grep to 
         standard error. This version number 
         should be included in all bug reports 
         (see below).
   -b, --byte-offset
         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, --revert-match option 
         (see below), count non-matching lines.
   -e PATTERN, 
       --regexp=PATTERN
         Use PATTERN as the pattern; 
         useful to protect patterns 
         beginning with -.
   -f FILE, 
       --file=FILE
         Obtain patterns from FILE, one per 
         line. The empty file contains zero 
         patterns, 
         and therefore matches nothing.
   -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
         Quiet; suppress normal output. The 
         scanning will stop on the first match.
   -s, --silent
         Suppress  error  messages about 
         nonexistent or unreadable files.
   -v, --revert-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.
   -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 is only supported on 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 is only supported on 
         MS-DOS and MS-Windows.

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 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 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 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 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.