grep.texi

来自「linux平台中」· TEXI 代码 · 共 1,814 行 · 第 1/5 页

@cindex dot
@cindex period
The period @samp{.} matches any single character.

@item ?
@opindex ?
@cindex question mark
@cindex match sub-expression at most once
The preceding item is optional and will be matched at most once.

@item *
@opindex *
@cindex asterisk
@cindex match sub-expression zero or more times
The preceding item will be matched zero or more times.

@item +
@opindex +
@cindex plus sign
The preceding item will be matched one or more times.

@item @{@var{n}@}
@opindex @{n@}
@cindex braces, one argument
@cindex match sub-expression n times
The preceding item is matched exactly @var{n} times.

@item @{@var{n},@}
@opindex @{n,@}
@cindex braces, second argument omitted
@cindex match sub-expression n or more times
The preceding item is matched n or more times.

@item @{@var{n},@var{m}@}
@opindex @{n,m@}
@cindex braces, two arguments
The preceding item is matched at least @var{n} times, but not more than
@var{m} times.

@end table

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 @samp{|}; 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.

@section Character Class

@cindex bracket expression
@cindex character class
A @dfn{bracket expression} is a list of characters enclosed by @samp{[} and
@samp{]}.  It matches any single character in that list; if the first
character of the list is the caret @samp{^}, then it matches any character
@strong{not} in the list.  For example, the regular expression
@samp{[0123456789]} matches any single digit.

@cindex range expression
Within a bracket expression, a @dfn{range expression} consists of two
characters separated by a hyphen.  It matches any single character that
sorts between the two characters, inclusive, using the locale's
collating sequence and character set.  For example, in the default C
locale, @samp{[a-d]} is equivalent to @samp{[abcd]}.  Many locales sort
characters in dictionary order, and in these locales @samp{[a-d]} is
typically not equivalent to @samp{[abcd]}; it might be equivalent to
@samp{[aBbCcDd]}, for example.  To obtain the traditional interpretation
of bracket expressions, you can use the C locale by setting the
@env{LC_ALL} environment variable to the value @samp{C}.

Finally, certain named classes of characters are predefined within
bracket expressions, as follows.
Their interpretation depends on the @code{LC_CTYPE} locale; the
interpretation below is that of the C locale, which is the default
if no @code{LC_CTYPE} locale is specified.

@cindex classes of characters
@cindex character classes
@table @samp

@item [:alnum:]
@opindex alnum
@cindex alphanumeric characters
Alphanumeric characters:
@samp{[:alpha:]} and @samp{[:digit:]}.

@item [:alpha:]
@opindex alpha
@cindex alphabetic characters
Alphabetic characters:
@samp{[:lower:]} and @samp{[:upper:]}.

@item [:blank:]
@opindex blank
@cindex blank characters
Blank characters:
space and tab.

@item [:cntrl:]
@opindex cntrl
@cindex control characters
Control characters.  In @sc{ascii}, these characters have octal codes 000
through 037, and 177 (@code{DEL}).  In other character sets, these are
the equivalent characters, if any.

@item [:digit:]
@opindex digit
@cindex digit characters
@cindex numeric characters
Digits: @code{0 1 2 3 4 5 6 7 8 9}.

@item [:graph:]
@opindex graph
@cindex graphic characters
Graphical characters:
@samp{[:alnum:]} and @samp{[:punct:]}.

@item [:lower:]
@opindex lower
@cindex lower-case letters
Lower-case letters:
@code{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}.

@item [:print:]
@opindex print
@cindex printable characters
Printable characters:
@samp{[:alnum:]}, @samp{[:punct:]}, and space.

@item [:punct:]
@opindex punct
@cindex punctuation characters
Punctuation characters:
@code{!@: " # $ % & ' ( ) * + , - .@: / : ; < = > ?@: @@ [ \ ] ^ _ ` @{ | @} ~}.

@item [:space:]
@opindex space
@cindex space characters
@cindex whitespace characters
Space characters:
tab, newline, vertical tab, form feed, carriage return, and space.

@item [:upper:]
@opindex upper
@cindex upper-case letters
Upper-case letters:
@code{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}.

@item [:xdigit:]
@opindex xdigit
@cindex xdigit class
@cindex hexadecimal digits
Hexadecimal digits:
@code{0 1 2 3 4 5 6 7 8 9 A B C D E F a b c d e f}.

@end table
For example, @samp{[[:alnum:]]} means @samp{[0-9A-Za-z]}, except the latter
depends upon the C locale and the @sc{ascii} 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.

@table @samp
@item ]
ends the list if it's not the first list item.  So, if you want to make
the @samp{]} character a list item, you must put it first.

@item [.
represents the open collating symbol.

@item .]
represents the close collating symbol.

@item [=
represents the open equivalence class.

@item =]
represents the close equivalence class.

@item [:
represents the open character class followed by a valid character class name.

@item :]
represents the close character class followed by a valid character class name.

@item -
represents the range if it's not first or last in a list or the ending point
of a range.

@item ^
represents the characters not in the list.  If you want to make the @samp{^}
character a list item, place it anywhere but first.

@end table

@section Backslash Character
@cindex backslash

The @samp{\} when followed by certain ordinary characters take a special
meaning :

@table @samp

@item @samp{\b}
Match the empty string at the edge of a word.

@item @samp{\B}
Match the empty string provided it's not at the edge of a word.

@item @samp{\<}
Match the empty string at the beginning of word.

@item @samp{\>}
Match the empty string at the end of word.

@item @samp{\w}
Match word constituent, it is a synonym for @samp{[[:alnum:]]}.

@item @samp{\W}
Match non word constituent, it is a synonym for @samp{[^[:alnum:]]}.

@end table

For example , @samp{\brat\b} matches the separate word @samp{rat},
@samp{c\Brat\Be} matches @samp{crate}, but @samp{dirty \Brat} doesn't
match @samp{dirty rat}.

@section Anchoring
@cindex anchoring

The caret @samp{^} and the dollar sign @samp{$} are metacharacters that
respectively match the empty string at the beginning and end of a line.

@section Back-reference
@cindex back-reference

The back-reference @samp{\@var{n}}, where @var{n} is a single digit, matches
the substring previously matched by the @var{n}th parenthesized subexpression
of the regular expression. For example, @samp{(a)\1} matches @samp{aa}.
When use with alternation if the group does not participate in the match, then
the back-reference makes the whole match fail.  For example, @samp{a(.)|b\1}
will not match @samp{ba}.  When multiple regular expressions are given with
@samp{-e} or from a file @samp{-f file}, the back-referecences are local to
each expression.

@section Basic vs Extended
@cindex basic regular expressions

In basic regular expressions the metacharacters @samp{?}, @samp{+},
@samp{@{}, @samp{|}, @samp{(}, and @samp{)} lose their special meaning;
instead use the backslashed versions @samp{\?}, @samp{\+}, @samp{\@{},
@samp{\|}, @samp{\(}, and @samp{\)}.

@cindex interval specifications
Traditional @command{egrep} did not support the @samp{@{} metacharacter,
and some @command{egrep} implementations support @samp{\@{} instead, so
portable scripts should avoid @samp{@{} in @samp{egrep} patterns and
should use @samp{[@{]} to match a literal @samp{@{}.

@sc{gnu} @command{egrep} attempts to support traditional usage by
assuming that @samp{@{} is not special if it would be the start of an
invalid interval specification.  For example, the shell command
@samp{egrep '@{1'} searches for the two-character string @samp{@{1}
instead of reporting a syntax error in the regular expression.
@sc{posix.2} allows this behavior as an extension, but portable scripts
should avoid it.

@node Usage
@chapter Usage

@cindex Usage, examples
Here is an example shell command that invokes @sc{gnu} @command{grep}:

@example
grep -i 'hello.*world' menu.h main.c
@end example

@noindent
This lists all lines in the files @file{menu.h} and @file{main.c} that
contain the string @samp{hello} followed by the string @samp{world};
this is because @samp{.*} matches zero or more characters within a line.
@xref{Regular Expressions}.  The @samp{-i} option causes @command{grep}
to ignore case, causing it to match the line @samp{Hello, world!}, which
it would not otherwise match.  @xref{Invoking}, for more details about
how to invoke @command{grep}.

@cindex Using @command{grep}, Q&A
@cindex FAQ about @command{grep} usage
Here are some common questions and answers about @command{grep} usage.

@enumerate

@item
How can I list just the names of matching files?

@example
grep -l 'main' *.c
@end example

@noindent
lists the names of all C files in the current directory whose contents
mention @samp{main}.

@item
How do I search directories recursively?

@example
grep -r 'hello' /home/gigi
@end example

@noindent
searches for @samp{hello} in all files under the directory
@file{/home/gigi}.  For more control of which files are searched, use
@command{find}, @command{grep} and @command{xargs}.  For example,
the following command searches only C files:

@smallexample
find /home/gigi -name '*.c' -print | xargs grep 'hello' /dev/null
@end smallexample

This differs from the command:

@example
grep -r 'hello' *.c
@end example

which merely looks for @samp{hello} in all files in the current
directory whose names end in @samp{.c}.  Here the @option{-r} is
probably unnecessary, as recursion occurs only in the unlikely event
that one of @samp{.c} files is a directory.

@item
What if a pattern has a leading @samp{-}?

@example
grep -e '--cut here--' *
@end example

@noindent
searches for all lines matching @samp{--cut here--}.  Without @samp{-e},
@command{grep} would attempt to parse @samp{--cut here--} as a list of
options.

@item
Suppose I want to search for a whole word, not a part of a word?

@example
grep -w 'hello' *
@end example

@noindent
searches only for instances of @samp{hello} that are entire words; it
does not match @samp{Othello}.  For more control, use @samp{\<} and
@samp{\>} to match the start and end of words.  For example:

@example