Regular expressions are string expressions which are used to identify matching patterns in other strings. Many languages and environments implement regular expressions, often with small differences. Regular expressions first gained large-scale use on unix systems in conjunction with tools such as grep, awk, and sed.

Simple Examples Edit

Example 1. literal (no special characters used) Edit

hello

Matches the string "hello" only.

Example 2. any character. Edit

the "." character matches any character except newline (\n).

an.

Matches "an!", "and"

Example 3. zero-or-more characters. Edit

the "*" character matches any string zero or more of the character immediately preceding it.

hel*

Matches "hel", "hellll"

External Links Edit

• Regular Expressions on Wikipedia
• Java Trail: Regular Expressions
• perlretut
• "Regular-Expressions.info - Regex Tutorial, Examples and Reference - Regexp Patterns" for many languages

See Also Edit

• Parsing
• Perl/Regular expressions
• PHP/Regular expressions
• Java/Regular expressions