grep, searching for a pattern
version 2.3, 10 February 1999
Alain Magloire et al.
Table of Contents
GREP searches the input files for lines containing a match to a given
pattern list. When it finds a match in a line, it copies the line to standard
output (by default), or does whatever other sort of output you have requested
with options. GREP expects to do the matching on text.
Since newline is also a separator for the list of patterns, there
is no way to match newline characters in a text.
GREP comes with a rich set of options from POSIX.2 and GNU extensions.
- `-c'
-
- `--count'
-
Suppress normal output; instead print a count of matching
lines for each input file. With the `-v', `--revert-match' option,
count non-matching lines.
- `-e pattern'
-
- `--regexp=pattern'
-
Use pattern as the pattern; useful to protect patterns
beginning with a `-'.
- `-f file'
-
- `--file=file'
-
Obtain patterns from file, one per line. The empty
file contains zero patterns, and therefore matches nothing.
- `-i'
-
- `--ignore-case'
-
Ignore case distinctions in both the pattern and the input files.
- `-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 of every file will stop on the first match.
- `-n'
-
- `--line-number'
-
Prefix each line of output with the line number within its input file.
- `-q'
-
- `--quiet'
-
- `--silent'
-
Quiet; suppress normal output. The scanning of every file will stop on
the first match. Also see the `-s' or `--no-messages' option.
- `-s'
-
- `--no-messages'
-
Suppress error messages about nonexistent or unreadable files.
Portability note: unlike GNU GREP, BSD GREP does not comply
with POSIX.2, because BSD GREP lacks a `-q' option and its
`-s' option behaves like GNU GREP's `-q' option. Shell
scripts intended to be portable to BSD GREP should avoid both
`-q' and `-s' and should redirect
output to `/dev/null' instead.
- `-v'
-
- `--revert-match'
-
Invert the sense of matching, to select non-matching lines.
- `-x'
-
- `--line-regexp'
-
Select only those matches that exactly match the whole line.
- `-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[=num]'
-
Print num lines (default 2) of output context.
- `-NUM'
-
Same as `--context=num' lines of leading and trailing
context. However, grep will never print any given line more than once.
- `-V'
-
- `--version'
-
Print the version number of GREP to the standard output stream.
This version number should be included in all bug reports.
- `--help'
-
Print a usage message briefly summarizing these command-line options
and the bug-reporting address, then exit.
- `-b'
-
- `--byte-offset'
-
Print the byte offset within the input file before each line of output.
When GREP runs on MS-DOS or MS-Windows, the printed byte offsets
depend on whether the `-u' (`--unix-byte-offsets') option is
used; see below.
- `-d action'
-
- `--directories=action'
-
If an input file is a directory, use action to process it.
By default, action is `read', which means that directories are
read just as if they were ordinary files (some operating systems
and filesystems disallow this, and will cause GREP to print error
messages for every directory). If action is `skip',
directories are silently skipped. If action is `recurse',
GREP reads all files under each directory, recursively; this is
equivalent to the `-r' option.
- `-h'
-
- `--no-filename'
-
Suppress the prefixing of filenames on output when multiple files are searched.
- `-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 of every file will stop on the first match.
- `-a'
-
- `--text'
-
Do not suppress output lines that contain binary data.
Normally, if the first few bytes of a file indicate
that the file contains binary data, grep outputs only a
message saying that the file matches the pattern. This
option causes grep to act as if the file is a text
file, even if it would otherwise be treated as binary.
Warning: the result might be binary garbage
printed to the terminal, which can have nasty
side-effects if the terminal driver interprets some of
it as commands.
- `-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.
- `-r'
-
- `--recursive'
-
For each directory mentioned in the command line, read and process all
files in that directory, recursively. This is the same as the `-d
recurse' option.
- `-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. the byte offsets ignore the CR characters which were
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.
Several additional options control which variant of the GREP
matching engine is used. See section GREP programs.
GREP uses the environment variable LANG to
provide internationalization support, if compiled with this feature.
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.
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. This is the default.
- `-E'
-
- `--extended-regexp'
-
Interpret pattern as an extended regular expression.
- `-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'.
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:]'
-
Any of [:digit:] or [:alpha:]
- `[:alpha:]'
-
Any local-specific or one of the ASCII letters:
a b c d e f g h i j k l m n o p q r s t u v w x y z
,
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
.
- `[:cntrl:]'
-
Any of
BEL
, BS
, CR
, FF
, HT
,
NL
, or VT
.
- `[:digit:]'
-
Any one of
0 1 2 3 4 5 6 7 8 9
.
- `[:graph:]'
-
Anything that is not a `[:alphanum:]' or `[:punct:]'.
- `[:lower:]'
-
Any one of
a b c d e f g h i j k l m n o p q r s t u v w x y z
.
- `[:print:]'
-
Any character from the `[:space:]' class, and any character that is
not in the `[:isgraph:]' class.
- `[:punct:]'
-
Any one of
! " #% & ' ( ) ; < = > ? [ \ ] * + , - . / : ^ _ { | }
.
- `[:space:]'
-
Any one of
CR FF HT NL VT SPACE
.
- `[:upper:]'
-
Any one of
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
.
- `[:xdigit:]'
-
Any one of
a b c d e f A B C D E F 0 1 2 3 4 5 6 7 8 9
.
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 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 may be followed by one of several
repetition operators:
- `?'
-
The preceding item is optional and will be 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 subexpression 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 `\{'. This not true for `grep -E'.
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.
This is a general index of all issues discussed in this manual, with the
exception of the GREP commands and command-line options.
Jump to:
a
-
b
-
c
-
d
-
f
-
g
-
h
-
l
-
m
-
n
-
p
-
q
-
r
-
s
-
u
-
v
-
w
-
x
after context
alphabetic characters
alphanumeric characters
asterisk
basic regular expressions
before context
binary files
binary files, DOS/Windows
braces, first argument omitted
braces, one argument
braces, second argument omitted
braces, two arguments
Bugs, reporting
byte offset
byte offsets, on DOS/Windows
case insensitive search
case insensitive search, obsolete option
character classes
classes of characters
context
context lines, after match
context lines, before match
control characters
counting lines
digit characters
directory search
DOS byte offsets
DOS/Windows binary files
files which don't match
graphic characters
hexadecimal digits
line numbering
lower-case alphabetic characters
match sub-expression at most m times
match sub-expression at most once
match sub-expression n or more times
match sub-expression n times
match sub-expression zero or more times
match the whole line
matching basic regular expressions
matching extended regular expressions
matching fixed strings
matching whole words
names of matching files
no filename prefix
numeric characters
pattern from file
pattern list
plus sign
print non-matching lines
printable characters
punctuation characters
question mark
quiet, silent
recursive search
regular expressions
revert matching
searching directory trees
Searching for a pattern.
space characters
suppress binary data
suppress error messages
upper-case alphabetic characters
Usage summary, printing
Version, printing
whitespace characters
xdigit class
This is an alphabetical list of all GREP commands and command-line
options.
Jump to:
This document was generated on 7 April 1999 using the
texi2html
translator version 1.52.