Download - The Bastards Book of Regular Expressions

Anchors: A way to trim emptinessIn a [previous chapter]{#plus-operator}, we learned how to match consecutive newline characters.This is handy when we want to remove blank lines from a text file.Another annoying whitespace problem occurs when there is padding between the beginning of theline and the first actual text character. For example, given these haikus¹⁶:do what you feel like since the work is abandoned the law doesn’t careif you use this code you and your children’s children must make your source freeI want them to be formatted so that the leading whitespace is removed and the lines are flush againstthe left-margin:do what you feel like since the work is abandoned the law doesn’t careif you use this code you and your children’s children must make your source freeThese “license haikus” are courtesy of Aaron Swartz¹⁷The caret as starting anchorWe need a way to match the beginning of the line. Think of it as a word-boundary ‐ remember\b? – except that we want a boundary for the entire line.To have a regex include the beginning of the line, use the caret: ˆThe following regex:^hello– will match the word hello if hellooccurs at the beginning of the line, as in the following example:hello goodbyeHowever, ˆhelloˆ will not match the hello in the following line:goodbye hello¹⁶http://www.aaronsw.com/weblog/000360¹⁷http://www.aaronsw.com/weblog/00036056