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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.


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.

Change following characters to lowercase until /E encountered.

\u Change single following character to uppercase.

Change following characters to uppercase until \E encountered.

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