Common Regular Expression Mistakes

1. Forgetting to enclose the regular expression in ' '.
2. Including spaces in the regular expressions (other than spaces you want).
3. Not escaping special characters you want treated literally: e.g. '()' instead of '\(\)'.
4. Forgetting the ^ and $ when you want an entire line to match a regular expression rather than some substring of the line.
5. Forgetting that something * includes the null string. For example, the regular expression (aaa|bbb)* matches every line!