Linux in a Nutshell, Fifth Edition

Metacharacters | 699

Pattern

Matching

This is the Title of the Book, eMatter Edition

Copyright © 2006 O’Reilly & Associates, Inc. All rights reserved.

Linux allows the use of POSIX “character classes” within the square brackets that

enclose a group of characters. They are typed enclosed in

[: and :]. For example,

[[:alnum:]] matches a single alphanumeric character.

Finally, the GNU utilities on Linux accept additional escape sequences that act

like metacharacters. (Because \b can also be interpreted as the sequence for the

ASCII Backspace character, different utilities treat it differently. Check each

utility’s documentation.)

Replacement Patterns

The characters in the following table have special meaning only in replacement

patterns.

? Match zero or one instances of preceding regular expression.

| Match the regular expression specified before or after the vertical bar (alternation).

( ) Apply a match to the enclosed group of regular expressions.

Class Characters matched Class Characters matched

alnum Alphanumeric characters lower Lowercase characters

alpha Alphabetic characters print Printable characters

blank Space or Tab punct Punctuation characters

cntrl Control characters space Whitespace characters

digit Decimal digits upper Uppercase characters

graph Non-space characters xdigit Hexadecimal digits

Sequence Meaning

\b Word boundary, either beginning or end of a word, as for the \< and \> metacharacters ...