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<table align="right"><tr valign="top"><td>[[Image:re-1.png|thumb|right|350px|Filename expansion symbols allow the Linux shell to expand filenames as arguments (referred to as “globbing”).]]</td><td>[[Image:re-2.png|thumb|right|250px|A regular expression is a combination of two types of characters: literals and special characters. In combination, these characters define a logical pattern. ''' command to display directory structure.]]</td></table>In a previous lesson, you learned that filename expansion symbols allow the Linux shell to expand filenames as arguments (referred to as “globbing”) for file management commands. This is very useful for managing multiple files sharing similar characteristics such as the same file extension.

[[Image:re-2.png|thumb|right|250px|A regular expression is a combination of two types of characters: literals and special characters. In combination, these characters define a logical pattern. ''' command to display directory structure.]]A '''regular expression''' is a combination of two types of characters: '''literals''' and '''special characters'''. In combination, these characters define a logical pattern. Strings of text can be compared to this pattern to see if they fit the pattern defined by the expression.