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],
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.