400 lines
8.6 KiB
Groff
400 lines
8.6 KiB
Groff
.TH GREP 1 "1992 September 10" "GNU Project"
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.SH NAME
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grep, egrep, fgrep \- print lines matching a pattern
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.SH SYNOPOSIS
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.B grep
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[\-[AB] num]
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[\-HRPS]
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[\-CEFGLVabchilnqsvwx]
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[\-e expr]
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[\-f file]
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files...
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.SH DESCRIPTION
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.PP
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.B Grep
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searches the named input
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.I files
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(or standard input if no files are named, or
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the file name
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.B \-
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is given)
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for lines containing a match to the given
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.IR pattern .
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By default,
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.B grep
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prints the matching lines.
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.PP
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There are three major variants of
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.BR grep ,
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controlled by the following options.
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.PD 0
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.TP
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.B \-G
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Interpret
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.I pattern
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as a basic regular expression (see below). This is the default.
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.TP
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.B \-E
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Interpret
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.I pattern
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as an extended regular expression (see below).
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.TP
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.B \-F
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Interpret
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.I pattern
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as a list of fixed strings, separated by newlines,
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any of which is to be matched.
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.LP
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In addition, two variant programs
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.B egrep
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and
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.B fgrep
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are available.
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.B Egrep
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is similiar (but not identical) to
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.BR "grep\ \-E" ,
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and is compatible with the historical Unix
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.BR egrep .
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.B Fgrep
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is the same as
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.BR "grep\ \-F" .
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.PD
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.LP
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All variants of
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.B grep
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understand the following options:
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.PD 0
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.TP
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.BI \- num
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Matches will be printed with
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.I num
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lines of leading and trailing context. However,
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.B grep
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will never print any given line more than once.
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.TP
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.BI \-A " num"
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Print
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.I num
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lines of trailing context after matching lines.
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.TP
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.BI \-B " num"
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Print
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.I num
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lines of leading context before matching lines.
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.TP
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.B \-C
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Equivalent to
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.BR \-2 .
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.TP
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.B \-V
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Print the version number of
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.B grep
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to standard error. This version number should
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be included in all bug reports (see below).
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.TP
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.B \-a
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Don't search in binary files.
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.TP
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.B \-b
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Print the byte offset within the input file before
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each line of output.
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.TP
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.B \-c
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Suppress normal output; instead print a count of
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matching lines for each input file.
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With the
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.B \-v
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option (see below), count non-matching lines.
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.TP
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.BI \-e " pattern"
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Use
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.I pattern
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as the pattern; useful to protect patterns beginning with
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.BR \- .
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.TP
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.BI \-f " file"
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Obtain the pattern from
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.IR file .
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.TP
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.B \-h
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Suppress the prefixing of filenames on output
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when multiple files are searched.
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.TP
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.B \-i
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Ignore case distinctions in both the
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.I pattern
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and the input files.
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.TP
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.B \-L
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Suppress normal output; instead print the name
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of each input file from which no output would
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normally have been printed.
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.TP
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.B \-l
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Suppress normal output; instead print
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the name of each input file from which output
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would normally have been printed.
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.TP
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.B \-n
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Prefix each line of output with the line number
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within its input file.
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.TP
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.B \-q
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Quiet; suppress normal output.
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.TP
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.B \-s
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Suppress error messages about nonexistent or unreadable files.
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.TP
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.B \-v
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Invert the sense of matching, to select non-matching lines.
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.TP
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.B \-w
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Select only those lines containing matches that form whole words.
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The test is that the matching substring must either be at the
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beginning of the line, or preceded by a non-word constituent
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character. Similarly, it must be either at the end of the line
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or followed by a non-word constituent character. Word-constituent
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characters are letters, digits, and the underscore.
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.TP
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.B \-x
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Select only those matches that exactly match the whole line.
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.PP
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Following options only avaible if compiled with FTS library:
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.PD 0
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.TP
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.BI \-H
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If the
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.I \-R
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option is specified, symbolic links on the command line
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are followed. (Symbolic links encountered in the tree traversal
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are not followed.)
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.TP
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.BI \-L
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If the
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.I \-R
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option is specified, all symbolic links are followed.
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.TP
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.BI \-P
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If the
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.I \-R
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option is specified, no symbolic links are followed.
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.TP
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.BI \-R
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Search in the file hierarchies
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rooted in the files instead of just the files themselves.
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.TP
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.PD
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.SH "REGULAR EXPRESSIONS"
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.PP
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A regular expression is a pattern that describes a set of strings.
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Regular expressions are constructed analagously to arithmetic
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expressions, by using various operators to combine smaller expressions.
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.PP
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.B Grep
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understands two different versions of regular expression syntax:
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``basic'' and ``extended.'' In
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.RB "GNU\ " grep ,
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there is no difference in available functionality using either syntax.
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In other implementations, basic regular expressions are less powerful.
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The following description applies to extended regular expressions;
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differences for basic regular expressions are summarized afterwards.
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.PP
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The fundamental building blocks are the regular expressions that match
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a single character. Most characters, including all letters and digits,
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are regular expressions that match themselves. Any metacharacter with
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special meaning may be quoted by preceding it with a backslash.
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.PP
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A list of characters enclosed by
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.B [
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and
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.B ]
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matches any single
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character in that list; if the first character of the list
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is the caret
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.B ^
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then it matches any character
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.I not
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in the list.
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For example, the regular expression
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.B [0123456789]
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matches any single digit. A range of ASCII characters
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may be specified by giving the first and last characters, separated
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by a hyphen.
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Finally, certain named classes of characters are predefined.
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Their names are self explanatory, and they are
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.BR [:alnum:] ,
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.BR [:alpha:] ,
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.BR [:cntrl:] ,
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.BR [:digit:] ,
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.BR [:graph:] ,
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.BR [:lower:] ,
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.BR [:print:] ,
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.BR [:punct:] ,
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.BR [:space:] ,
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.BR [:upper:] ,
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and
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.BR [:xdigit:].
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For example,
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.B [[:alnum:]]
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means
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.BR [0-9A-Za-z] ,
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except the latter form is dependent upon the ASCII character encoding,
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whereas the former is portable.
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(Note that the brackets in these class names are part of the symbolic
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names, and must be included in addition to the brackets delimiting
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the bracket list.) Most metacharacters lose their special meaning
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inside lists. To include a literal
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.B ]
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place it first in the list. Similarly, to include a literal
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.B ^
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place it anywhere but first. Finally, to include a literal
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.B \-
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place it last.
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.PP
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The period
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.B .
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matches any single character.
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The symbol
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.B \ew
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is a synonym for
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.B [[:alnum:]]
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and
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.B \eW
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is a synonym for
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.BR [^[:alnum]] .
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.PP
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The caret
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.B ^
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and the dollar sign
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.B $
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are metacharacters that respectively match the empty string at the
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beginning and end of a line.
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The symbols
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.B \e<
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and
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.B \e>
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respectively match the empty string at the beginning and end of a word.
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The symbol
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.B \eb
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matches the empty string at the edge of a word,
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and
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.B \eB
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matches the empty string provided it's
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.I not
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at the edge of a word.
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.PP
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A regular expression matching a single character may be followed
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by one of several repetition operators:
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.PD 0
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.TP
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.B ?
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The preceding item is optional and matched at most once.
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.TP
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.B *
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The preceding item will be matched zero or more times.
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.TP
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.B +
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The preceding item will be matched one or more times.
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.TP
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.BI { n }
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The preceding item is matched exactly
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.I n
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times.
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.TP
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.BI { n ,}
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The preceding item is matched
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.I n
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or more times.
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.TP
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.BI {, m }
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The preceding item is optional and is matched at most
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.I m
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times.
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.TP
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.BI { n , m }
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The preceding item is matched at least
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.I n
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times, but not more than
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.I m
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times.
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.PD
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.PP
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Two regular expressions may be concatenated; the resulting
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regular expression matches any string formed by concatenating
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two substrings that respectively match the concatenated
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subexpressions.
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.PP
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Two regular expressions may be joined by the infix operator
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.BR | ;
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the resulting regular expression matches any string matching
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either subexpression.
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.PP
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Repetition takes precedence over concatenation, which in turn
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takes precedence over alternation. A whole subexpression may be
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enclosed in parentheses to override these precedence rules.
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.PP
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The backreference
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.BI \e n\c
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\&, where
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.I n
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is a single digit, matches the substring
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previously matched by the
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.IR n th
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parenthesized subexpression of the regular expression.
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.PP
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In basic regular expressions the metacharacters
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.BR ? ,
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.BR + ,
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.BR { ,
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.BR | ,
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.BR ( ,
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and
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.BR )
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lose their special meaning; instead use the backslashed
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versions
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.BR \e? ,
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.BR \e+ ,
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.BR \e{ ,
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.BR \e| ,
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.BR \e( ,
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and
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.BR \e) .
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.PP
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In
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.B egrep
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the metacharacter
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.B {
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loses its special meaning; instead use
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.BR \e{ .
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.SH DIAGNOSTICS
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.PP
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Normally, exit status is 0 if matches were found,
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and 1 if no matches were found. (The
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.B \-v
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option inverts the sense of the exit status.)
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Exit status is 2 if there were syntax errors
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in the pattern, inaccessible input files, or
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other system errors.
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.SH BUGS
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.PP
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Email bug reports to
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.BR bug-gnu-utils@prep.ai.mit.edu .
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Be sure to include the word ``grep'' somewhere in the ``Subject:'' field.
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.PP
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Large repetition counts in the
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.BI { m , n }
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construct may cause grep to use lots of memory.
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In addition,
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certain other obscure regular expressions require exponential time
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and space, and may cause
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.B grep
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to run out of memory.
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.PP
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Backreferences are very slow, and may require exponential time.
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