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-mes-
sages] [--revert-match] [--version] [--help] [--byte-off-
set] [--line-number] [--with-filename] [--no-filename]
[--quiet] [--silent] [--files-without-match] [--files-
with-matcces] [--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, sepa-
rated 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-match-
ing lines.
-e PATTERN, --regexp=PATTERN
Use PATTERN as the pattern; useful to protect pat-
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, --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-match-
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-
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, --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 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
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 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
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@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.