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    copied!<p>I use them quite frequently, probably because I'm mostly in a linux environment and have easy access to them.</p> <ul> <li>Searching for things in an editor, especially when I know two parts on a line but not what is inbetween (please excuse the extraneous whitespace) <ul> <li>Where is the reval function that takes a widget? "<code>reval.*\&lt;widget\&lt;</code>"</li> <li>Where is my_obj assigned to? "<code>\&lt;my_obj\&gt;.*=</code>"</li> </ul></li> <li>To search and replace in order to produce a modification of a data file: i.e., set all the delivery volumes to one "<code>#&lt;volume&gt;[-0-9.]+&lt;/volume&gt;#&lt;volume&gt;1.0&lt;/volume&gt;</code>#g"</li> <li>To munge output to fit on the screen (removing whitespace or uninteresting fields).</li> <li>To munge data files into another format, such as taking log files and producing a file for gnuplot which graphs performance data.</li> <li>For programmatic uses, such as pattern matching a data value's name in order to handle it differently if it matches certain criteria most easily expressed with a regular expression.</li> </ul> <p>After using regexes I hate the windows "Find" box because it is so limited.</p> <p>As another user answered, regular expressions are essentially more powerful globbing, but they go way beyond that. You don't need to read <a href="http://oreilly.com/catalog/9781565922570/" rel="nofollow noreferrer">"Master Regular Expressions"</a> to use them, but I do recommend the book. I'm sure there are plenty of resources on the internet, such as <a href="http://www.regular-expressions.info/" rel="nofollow noreferrer">here</a>, although I can't vouch for any of them.</p> <p>Another advantage to using regular expressions (whether in code or on the command line) is that they have been heavily optimized. Grep and <a href="http://en.wikipedia.org/wiki/21st_Century_Compilers" rel="nofollow noreferrer">DFA parsers</a> in particular are almost certainly faster than what you would write on your own... and more likely to be correct the first time. Don't reinvent the wheel when you have such a nice one handy.</p>
 

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