#  ____  _____ ____ _______  ______
# |  _ \| ____/ ___| ____\ \/ /  _ \
# | |_) |  _|| |  _|  _|  \  /| |_) |
# |  _ <| |__| |_| | |___ /  \|  __/
# |_| \_\_____\____|_____/_/\_\_|

Regular Expressions

It was debated whether to include this section under programming languages, or create a section for itself outside of the programming language tree, and it was decided the importance of understanding regular expressions entitled it to a section all to itself.

So, what is REGEXP? REGEXP, also abbreviated REGEX (preferred), is an acronym for “Regular Expressions”. REGEX can be summarized in one word, “matching”. IF you wanted to be more technical, “Pattern Matching”. Using REGEX allows the user to match complex patterns and search text with a realtively high precision. It is distinct from globbing, due to it’s extensiveness and complexity. Where globbing primarily relies on wildcard symbols/characters, the forumulation of a regular expression is very technical and can incorporate any number and/or combination of characters and symbols.

REGEX also comes in many forms, and nearly every programming language has it’s own REGEX syntax. The Perl Common Regular Expressions is the most commonly accepted REGEX syntax, but it is not universally accepted, not by a long shot. Although REGEX has many variations, there are some symbols that are almost always the same regardless of what language the syntax is in. These are referred to as wildcards, and wildcards includes symbols like *, +, and .. Furthermore, regex often is indicated by it’s inclusion in backslashes, sometimes begins with a ^ and ends with a $.

This was supposed to be a closing sentence, but unfortunately I can’t think of what else to write. So, I will leave a regex here for you to match yourself.

/^[-a-zA-Z0-9\ \.]*$/

Javascript REGEX

In JS a regex expression is placed between two backslashes followed by a flag to indicate what the REGEX is supposed to be used for, or what is the language supposed to do with it. A table of JS regex flags is found below.

So taking what we already know, a regex to match any character one or more times would look like: \.+\g.

A noncapturing group, referred to as a fixed string in other languages, is written like so: \(?:string)\g

Sources

• Regexer
• Regex and Globbing