Commonly used regular expressions - Cheatsheet

You can write regular expressions some different ways, e.g. /regex/ and %r{regex}. For examples, look here.

Remember that it is always a good idea [to matc...

When you repeat a subpattern with a *, + or {...} operator, you may choose between greedy, lazy and possessive modes.

Switching modes may affect the result and performance of your regular expressions. In the worst case, an ill-s...

The following two hints are taken from Github's Ruby style guide:

If your regular expression mentions a lot of forward slashes, you can use the alternative delimiters %r(...), %r[...] or %r{...} instead...

When you have many changes, and you want to spread them across different commits, here is a way to stage all changes matching a given regular expression for a single commit.

Example

Consider the following git diff output.

diff --gi...

Regular expressions in Javascript are represented by a RegExp object. There also is a regex literal as in many other languages: /regex/. However, they are used slightly differently.

Regex literal

• Usage: /foo+/
• Shorthand for creat...

Matching the "space" character class

For matching whitespaces in a regular expression, the most common and best-known shorthand expression is probably \s.
It matches the following whitespace characters:

• " " (space)
• \n (newline)
• \r (...

Regular expressions can have something called "zero-width look-behind assertions". This means that you want a pattern to be preceded by another pattern, but not include the preceding pattern in your match or search cursor. E.g. (?<=x)y matches `...

Developing complex regular expressions quickly blows my mind. Here are some online regex editors that help you by highlighting matching text and capture groups:

• Ruby:
  • Rubular
• Javascript:
  • [RegExr](http:/...

Ruby's regular expressions can be represented differently.
When serializing them, you probably want to use inspect instead of to_s.

For the examples below, consider the following Regexp object.

regexp = /^f(o+)!/mi

to_s

Using ...

A little-known feature of modern Regexp engines that help when optimizing a pattern that will be matched against long strings:

An atomic group is a group that, when the regex engine exits from it, automatically throws away all backtracking posi...