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Regular Expression Tutorial
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Optional Quantifier

The optional quantifier, "?", matches the character it's modifying zero or one times. This basically provides a mechanism to have a character be optional.

re-May_07

This will match "May 07" and "May 7".

This will find military time formats.

re-militarytime

Finds "04:33", "21:15", "12:00", "00:00". The optional quantifier allows matches with non-military time such as "8:45" and "2:30". This also means that "0:15" is matched. It will also incorrectly match string such as "27:45". It does not find "30:00", "12:82", etc.

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Chris X. Edwards ~ December 2003