208: Regular Expressions

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Regular Expressions

Title text: Wait, forgot to escape a space. Wheeeeee[taptaptap]eeeeee.

Explanation

In computing, a regular expression provides a concise and flexible means to "match" (specify and recognize) strings of text, such as particular characters, words, or patterns of characters.

Looking for a specific pattern on 200MB of text is an equivalent to "looking for a needle in a haystack" (Considering UTF-32 (32bits per character), this would be over 5 million characters. This task can be made easy by using "regexes", since they can find "match" a specific string pattern on the text.

Perl is a popular scripting language, and is especially well known for the flexible and simple regular expression features that it offers.

Trivia

This comic is featured on one of the T-shirts sold at the xkcd store

Transcript

Narrator: Whenever I learn a new skill I concoct elaborate fantasy scenarios where it lets me save the day.

Megan: Oh no! The killer must have followed her on vacation!

[Megan points to computer]

Megan: But to find them we'd need to search through 200MB of emails looking for something formatted like an address!

Cueball: It's hopeless!

Offpanel voice: Everybody stand back.

Offpanel voice: I know regular expressions.

[A man swings in on a rope, toward the computer]

tap tap

PERL!

[The man swings away, and the other characters cheer]

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Discussion

Hi, sorry about the previous "poor explanation". This one is pretty straight-forward (I think), given enough information about "regex"es and Perl. On a side-note, how did you find out the date for the comic? -- NariOx

The explanation was mostly accurate, my gripe was with the fact that a number of fields were empty - the transcript, date and categories weren't done. You can find the date in the "all comics" page, accessible from the sidebar. Davidy²²[talk] 23:26, 29 November 2012 (UTC)