Bracket Expressions and Character Classes

In addition to matching any character at a given position in our regular expression, we can also match a single character from a specified set of characters by using bracket expressions. With bracket expressions, we can specify a set of characters (including characters that would otherwise be interpreted as metacharacters) to be matched. In this example, using a two-character set, we match any line that contains the string bzip or gzip:

[me@linuxbox ˜]$ grep -h '[bg]zip' dirlist*.txt
bzip2
bzip2recover
gzip

A set may contain any number of characters, and metacharacters lose their special meaning when placed within brackets. However, there are two cases in which metacharacters are used within bracket expressions ...

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