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.Id $Id: grep.1,v 1.7 2003/04/25 21:09:43 deraadt Exp $
.TH GREP 1 \*(Dt "GNU Project"
.SH NAME
grep, egrep, fgrep \- print lines matching a pattern
.SH SYNOPSIS
.B grep
.RI [ options ]
.I PATTERN
.RI [ FILE .\|.\|.]
.br
.B grep
.RI [ options ]
.RB [ \-e
.I PATTERN
|
.B \-f
.IR FILE ]
.RI [ FILE .\|.\|.]
.SH DESCRIPTION
.PP
.B Grep
searches the named input
.IR FILE s
(or standard input if no files are named, or
the file name
.B \-
is given)
for lines containing a match to the given
.IR PATTERN .
By default,
.B grep
prints the matching lines.
.PP
In addition, two variant programs
.B egrep
and
.B fgrep
are available.
.B Egrep
is the same as
.BR "grep\ \-E" .
.B Fgrep
is the same as
.BR "grep\ \-F" .
.SH OPTIONS
.TP
.BI \-A " NUM" "\fR,\fP \-\^\-after-context=" NUM
Print
.I NUM
lines of trailing context after matching lines.
.TP
.BR \-a ", " \-\^\-text
Process a binary file as if it were text; this is equivalent to the
.B \-\^\-binary-files=text
option.
.TP
.BI \-B " NUM" "\fR,\fP \-\^\-before-context=" NUM
Print
.I NUM
lines of leading context before matching lines.
.TP
\fB\-C\fP [\fINUM\fP], \fB\-\fP\fINUM\fP, \fB\-\^\-context\fP[\fB=\fP\fINUM\fP]
Print
.I NUM
lines (default 2) of output context.
.TP
.BR \-b ", " \-\^\-byte-offset
Print the byte offset within the input file before
each line of output.
.TP
.BI \-\^\-binary-files= TYPE
If the first few bytes of a file indicate that the file contains binary
data, assume that the file is of type
.IR TYPE .
By default,
.I TYPE
is
.BR binary ,
and
.B grep
normally outputs either
a one-line message saying that a binary file matches, or no message if
there is no match.
If
.I TYPE
is
.BR without-match ,
.B grep
assumes that a binary file does not match; this is equivalent to the
.B \-I
option.
If
.I TYPE
is
.BR text ,
.B grep
processes a binary file as if it were text; this is equivalent to the
.B \-a
option.
.I Warning:
.B "grep \-\^\-binary-files=text"
might output binary garbage,
which can have nasty side effects if the output is a terminal and if the
terminal driver interprets some of it as commands.
.TP
.BR \-c ", " \-\^\-count
Suppress normal output; instead print a count of
matching lines for each input file.
With the
.BR \-v ", " \-\^\-invert-match
option (see below), count non-matching lines.
.TP
.BI \-d " ACTION" "\fR,\fP \-\^\-directories=" ACTION
If an input file is a directory, use
.I ACTION
to process it.  By default,
.I ACTION
is
.BR read ,
which means that directories are read just as if they were ordinary files.
If
.I ACTION
is
.BR skip ,
directories are silently skipped.
If
.I ACTION
is
.BR recurse ,
.B grep
reads all files under each directory, recursively;
this is equivalent to the
.B \-r
option.
.TP
.BR \-E ", " \-\^\-extended-regexp
Interpret
.I PATTERN
as an extended regular expression (see below).
.TP
.BI \-e " PATTERN" "\fR,\fP \-\^\-regexp=" PATTERN
Use
.I PATTERN
as the pattern; useful to protect patterns beginning with
.BR \- .
.TP
.BR \-F ", " \-\^\-fixed-strings
Interpret
.I PATTERN
as a list of fixed strings, separated by newlines,
any of which is to be matched.
.TP
.BI \-f " FILE" "\fR,\fP \-\^\-file=" FILE
Obtain patterns from
.IR FILE ,
one per line.
The empty file contains zero patterns, and therefore matches nothing.
.TP
.BR \-G ", " \-\^\-basic-regexp
Interpret
.I PATTERN
as a basic regular expression (see below).  This is the default.
.TP
.BR \-H ", " \-\^\-with-filename
Print the filename for each match.
.TP
.BR \-h ", " \-\^\-no-filename
Suppress the prefixing of filenames on output
when multiple files are searched.
.TP
.B \-\^\-help
Output a brief help message.
.TP
.BR \-I
Process a binary file as if it did not contain matching data; this is
equivalent to the
.B \-\^\-binary-files=without-match
option.
.TP
.BR \-i ", " \-\^\-ignore-case
Ignore case distinctions in both the
.I PATTERN
and the input files.
.TP
.BR \-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.
.TP
.BR \-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.
.TP
.B \-\^\-mmap
If possible, use the
.BR mmap (2)
system call to read input, instead of
the default
.BR read (2)
system call.  In some situations,
.B \-\^\-mmap
yields better performance.  However,
.B \-\^\-mmap
can cause undefined behavior (including core dumps)
if an input file shrinks while
.B grep
is operating, or if an I/O error occurs.
.TP
.BR \-n ", " \-\^\-line-number
Prefix each line of output with the line number
within its input file.
.TP
.BR \-q ", " \-\^\-quiet ", " \-\^\-silent
Quiet; suppress normal output.  The scanning will stop
on the first match.
Also see the
.B \-s
or
.B \-\^\-no-messages
option below.
.TP
.BR \-r ", " \-\^\-recursive
Read all files under each directory, recursively;
this is equivalent to the
.B "\-d recurse"
option.
.TP
.BR \-s ", " \-\^\-no-messages
Suppress error messages about nonexistent or unreadable files.
Portability note: unlike \s-1GNU\s0
.BR grep ,
traditional
.B grep
did not conform to \s-1POSIX.2\s0, because traditional
.B grep
lacked a
.B \-q
option and its
.B \-s
option behaved like \s-1GNU\s0
.BR grep 's
.B \-q
option.
Shell scripts intended to be portable to traditional
.B grep
should avoid both
.B \-q
and
.B \-s
and should redirect output to /dev/null instead.
.TP
.BR \-U ", " \-\^\-binary
Treat the file(s) as binary.  By default, under MS-DOS and MS-Windows,
.BR grep
guesses the file type by looking at the contents of the first 32KB
read from the file.  If
.BR grep
decides the file is a text file, it strips the CR characters from the
original file contents (to make regular expressions with
.B ^
and
.B $
work correctly).  Specifying
.B \-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.
.TP
.BR \-u ", " \-\^\-unix-byte-offsets
Report Unix-style byte offsets.  This switch causes
.B 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
.B grep
on a Unix machine.  This option has no effect unless
.B \-b
option is also used;
it has no effect on platforms other than MS-DOS and MS-Windows.
.TP
.BR \-V ", " \-\^\-version
Print the version number of
.B grep
to standard error.  This version number should
be included in all bug reports (see below).
.TP
.BR \-v ", " \-\^\-invert-match
Invert the sense of matching, to select non-matching lines.
.TP
.BR \-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.
.TP
.BR \-x ", " \-\^\-line-regexp
Select only those matches that exactly match the whole line.
.TP
.B \-y
Obsolete synonym for
.BR \-i .
.TP
.BR \-Z ", " \-\^\-null
Output a zero byte (the \s-1ASCII\s0
.B NUL
character) instead of the character that normally follows a file name.
For example,
.B "grep \-lZ"
outputs a zero byte after each file name instead of the usual newline.
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
.BR "find \-print0" ,
.BR "perl \-0" ,
.BR "sort \-z" ,
and
.B "xargs \-0"
to process arbitrary file names,
even those that contain newline characters.
.SH "REGULAR EXPRESSIONS"
.PP
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.
.PP
.B Grep
understands two different versions of regular expression syntax:
\*(lqbasic\*(rq and \*(lqextended.\*(rq  In
.RB "\s-1GNU\s0\ " 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.
.PP
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.
.PP
A list of characters enclosed by
.B [
and
.B ]
matches any single
character in that list; if the first character of the list
is the caret
.B ^
then it matches any character
.I not
in the list.
For example, the regular expression
.B [0123456789]
matches any single digit.  A range of 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
.BR [:alnum:] ,
.BR [:alpha:] ,
.BR [:cntrl:] ,
.BR [:digit:] ,
.BR [:graph:] ,
.BR [:lower:] ,
.BR [:print:] ,
.BR [:punct:] ,
.BR [:space:] ,
.BR [:upper:] ,
and
.BR [:xdigit:].
For example,
.B [[:alnum:]]
means
.BR [0-9A-Za-z] ,
except the latter form depends upon the \s-1POSIX\s0 locale and the
\s-1ASCII\s0 character encoding, whereas the former is independent
of locale and character set.
(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
.B ]
place it first in the list.  Similarly, to include a literal
.B ^
place it anywhere but first.  Finally, to include a literal
.B \-
place it last.
.PP
The period
.B .
matches any single character.
The symbol
.B \ew
is a synonym for
.B [[:alnum:]]
and
.B \eW
is a synonym for
.BR [^[:alnum\:]] .
.PP
The caret
.B ^
and the dollar sign
.B $
are metacharacters that respectively match the empty string at the
beginning and end of a line.
The symbols
.B \e<
and
.B \e>
respectively match the empty string at the beginning and end of a word.
The symbol
.B \eb
matches the empty string at the edge of a word,
and
.B \eB
matches the empty string provided it's
.I not
at the edge of a word.
.PP
A regular expression may be followed by one of several repetition operators:
.PD 0
.TP
.B ?
The preceding item is optional and matched at most once.
.TP
.B *
The preceding item will be matched zero or more times.
.TP
.B +
The preceding item will be matched one or more times.
.TP
.BI { n }
The preceding item is matched exactly
.I n
times.
.TP
.BI { n ,}
The preceding item is matched
.I n
or more times.
.TP
.BI { n , m }
The preceding item is matched at least
.I n
times, but not more than
.I m
times.
.PD
.PP
Two regular expressions may be concatenated; the resulting
regular expression matches any string formed by concatenating
two substrings that respectively match the concatenated
subexpressions.
.PP
Two regular expressions may be joined by the infix operator
.BR | ;
the resulting regular expression matches any string matching
either subexpression.
.PP
Repetition takes precedence over concatenation, which in turn
takes precedence over alternation.  A whole subexpression may be
enclosed in parentheses to override these precedence rules.
.PP
The backreference
.BI \e n\c
\&, where
.I n
is a single digit, matches the substring
previously matched by the
.IR n th
parenthesized subexpression of the regular expression.
.PP
In basic regular expressions the metacharacters
.BR ? ,
.BR + ,
.BR { ,
.BR | ,
.BR ( ,
and
.BR )
lose their special meaning; instead use the backslashed
versions
.BR \e? ,
.BR \e+ ,
.BR \e{ ,
.BR \e| ,
.BR \e( ,
and
.BR \e) .
.PP
Traditional
.B egrep
did not support the
.B {
metacharacter, and some
.B egrep
implementations support
.B \e{
instead, so portable scripts should avoid
.B {
in
.B egrep
patterns and should use
.B [{]
to match a literal
.BR { .
.PP
\s-1GNU\s0
.B egrep
attempts to support traditional usage by assuming that
.B {
is not special if it would be the start of an invalid interval
specification.  For example, the shell command
.B "egrep '{1'"
searches for the two-character string
.B {1
instead of reporting a syntax error in the regular expression.
\s-1POSIX.2\s0 allows this behavior as an extension, but portable scripts
should avoid it.
.SH "ENVIRONMENT VARIABLES"
.TP
.B GREP_OPTIONS
This variable specifies default options to be placed in front of any
explicit options.  For example, if
.B GREP_OPTIONS
is
.BR "'\-\^\-binary-files=without-match \-\^\-directories=skip'" ,
.B grep
behaves as if the two options
.B \-\^\-binary-files=without-match
and
.B \-\^\-directories=skip
had been specified before any explicit options.
Option specifications are separated by whitespace.
A backslash escapes the next character,
so it can be used to specify an option containing whitespace or a backslash.
.TP
\fBLC_ALL\fP, \fBLC_MESSAGES\fP, \fBLANG\fP
These variables specify the
.B LC_MESSAGES
locale, which determines the language that
.B grep
uses for messages.
The locale is determined by the first of these variables that is set.
American English is used if none of these environment variables are set,
or if the message catalog is not installed, or if
.B grep
was not compiled with national language support (\s-1NLS\s0).
.TP
\fBLC_ALL\fP, \fBLC_CTYPE\fP, \fBLANG\fP
These variables specify the
.B LC_CTYPE
locale, which determines the type of characters, e.g., which
characters are whitespace.
The locale is determined by the first of these variables that is set.
The \s-1POSIX\s0 locale is used if none of these environment variables
are set, or if the locale catalog is not installed, or if
.B grep
was not compiled with national language support (\s-1NLS\s0).
.TP
.B POSIXLY_CORRECT
If set,
.B grep
behaves as \s-1POSIX.2\s0 requires; otherwise,
.B grep
behaves more like other \s-1GNU\s0 programs.
\s-1POSIX.2\s0 requires that options that follow file names must be
treated as file names; by default, such options are permuted to the
front of the operand list and are treated as options.
Also, \s-1POSIX.2\s0 requires that unrecognized options be diagnosed as
\*(lqillegal\*(rq, but since they are not really against the law the default
is to diagnose them as \*(lqinvalid\*(rq.
.B POSIXLY_CORRECT
also disables \fB_\fP\fIN\fP\fB_GNU_nonoption_argv_flags_\fP,
described below.
.TP
\fB_\fP\fIN\fP\fB_GNU_nonoption_argv_flags_\fP
(Here
.I N
is
.BR grep 's
numeric process ID.)  If the
.IR i th
character of this environment variable's value is
.BR 1 ,
do not consider the
.IR i th
operand of
.B grep
to be an option, even if it appears to be one.
A shell can put this variable in the environment for each command it runs,
specifying which operands are the results of file name wildcard
expansion and therefore should not be treated as options.
This behavior is available only with the \s-1GNU\s0 C library, and only
when
.B POSIXLY_CORRECT
is not set.
.SH DIAGNOSTICS
.PP
Normally, exit status is 0 if matches were found,
and 1 if no matches were found.  (The
.B \-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.
.SH BUGS
.PP
Email bug reports to
.BR bug-gnu-utils@gnu.org .
Be sure to include the word \*(lqgrep\*(rq somewhere in the
\*(lqSubject:\*(rq field.
.PP
Large repetition counts in the
.BI { 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
.B grep
to run out of memory.
.PP
Backreferences are very slow, and may require exponential time.
.\" Work around problems with some troff -man implementations.
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