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<span style="color:blue;font-weight:bold;font-family:courier;">grep Linux document.txt</span><br><br>

The problem with using literals or simple regular expressions is that only <u>simple</u> or <u>general</u> patterns are matched.

<table align="left"><tr valign="top"><td>[[Image:re-4.png|thumb|right|200px|Example of using '''anchors'''.]]</td><td>[[Image:re-5.png|thumb|right|175px|Example of matching by '''character(s)'''.]]</td><td>[[Image:re-6.png|thumb|right|220px|Example of using '''character class'''.]]</td><td>[[Image:re-7.png|thumb|right|200px|Example of matching '''zero or more occurrence of preceding character'''.]]</td></tr></table>

===Extended Regular Expressions===