NAME
grep, egrep, fgrep - print lines matching a pattern
SYNOPSIS
grep [-AB] num] [-CEFGVbchiLlnqsvwxyUu] [-e pattern | -f
file] [--extended-regexp] [--fixed-strings] [--basic-regexp]
[--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-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 con-
taining 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 avail-
able. 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 match-
ing 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 the pattern from file.
-h, --no-filename
Suppress the prefixing of filenames on output when mul-
tiple 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 pre-
ceded 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 com-
bine 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 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 explana-
tory, 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. Simi-
larly, 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 matching a single character may be fol-
lowed 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 concatenat-
ing 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 subexpres-
sion may be enclosed in parentheses to override these pre-
cedence 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.
BUGS
Email bug reports to bug-gnu-utils@prep.ai.mit.edu. 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.
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