Regular expressions

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Regular Expressions (regex) are essentially a search engine for finding patterns in a text. While the syntax is a bit tricky to learn, regex will save tons of time and effort in the long run. Many of you are probably familiar with regex, even if only through the use of wildcards. Wildcard notation, such as *.html, matches to all html files in the given search directory. Regex takes this idea and expands on it dramatically, allowing for very complicated search patterns. A regular expression to find all html files in a given directory would be .*\.html$

Syntax

Characters

Literals

The most basic regex is a literal character. A literal character, such as a matches a in the string alex. However, in a string such as adam, it will only match the first a, before the 'd', unless you tell the regex engine otherwise. Most text editors that have a 'find' function, also have a 'find next' function.

Similarly, a regex search for hat in the string Blackhat Academy will return 'hat' from the end of the first word. This is merely a string of literal characters, and the regex engine handles it the same way as it handles a single literal character.

Tools

Utilities

• grep
• grepWin
• RegexPal

Programming Languages

• Gnulib
• Java
• JavaScript
• .NET
• Perl
• PHP
• PowerShell
• Python
• Ruby

Databases

• MySQL
• Oracle
• PostgreSQL