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9.2. Metacharacters, Listed by Linux Program

Some metacharacters are valid for one program but not for another. Those that are available to a given program are marked by a bullet () in the following table. Notes are provided after the table, and full descriptions of metacharacters are in the following section.

Symbol ed vi sed awk grep egrep Action
.

Match any character (can match newline in gawk).

*

Match zero or more preceding.

^

Match beginning of line or string.

$

Match end of line or string.

\

Escape character following.

[]

Match one from a list or range.

\(\)

Store pattern for later replay.

\n

Reuse matched text stored in nth \( \).

{}

Match a range of instances.

\{\}

Match a range of instances.

\<\>

Match word's beginning or end.

+

Match one or more preceding.

?

Match zero or one preceding.

|

Separate choices to match.

()

Group expressions to match.

On some Linux systems, grep is a link to egrep, so whenever you run grep you actually get egrep behavior.

In ed, vi, and sed, when you perform a search-and-replace (substitute) operation, the metacharacters in this table apply to the pattern you are searching for but not to the string replacing it.

In awk, {} is specified in the POSIX standard and is supported by gawk if you run it with the -Wre-interval option.

In ed, vi, and sed, the following additional metacharacters are valid only in a replacement pattern:

Symbol ex sed ed Action
\ Escape character following.
\n Reuse matched text stored in nth \( \).
& Reuse previous search pattern.
~ Reuse previous replacement pattern.
\e Turn off previous \L or \U.
\E Turn off previous /L or /U.
\l Change single following character to lowercase.
\L

Change following characters to lowercase until /E encountered.

\u Change single following character to uppercase.
\U

Change following characters to uppercase until \E encountered.



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