Perl language structure: Difference between revisions

Revision as of 09:03, 27 March 2014

Revision as of 09:39, 5 April 2014

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The Perl language includes a specialized syntax for writing [[regular expression]]s (RE, or regexes), and the interpreter contains an engine for matching strings to regular expressions. The regular-expression engine uses a [[backtracking]] algorithm, extending its capabilities from simple pattern matching to string capture and substitution. The regular-expression engine is derived from regex written by [[Henry Spencer]].

The Perl regular-expression syntax was originally taken from Unix Version 8 regular expressions. However, it diverged before the first release of Perl and has since grown to include far more features. Many other languages and applications are now adopting [[PCRE|Perl compatibleCompatible regularRegular expressionsExpressions]] over [[POSIX]] regular expressions, such as [[PHP]], [[Ruby programming language|Ruby]], [[Java (programming language)|Java]], Microsoft's [[.NET Framework]],<ref>Microsoft Corp., ".NET Framework Regular Expressions", ''.NET Framework Developer's Guide'', [http://msdn2.microsoft.com/en-us/library/hs600312(VS.71).aspx]</ref> and the [[Apache HTTP server]].

Regular-expression syntax is extremely compact, owing to history. The first regular-expression dialects were only slightly more expressive than [[Glob (programming)|globs]], and the syntax was designed so that an expression would resemble the text that it matches.{{Citation needed|date=June 2007}} This meant using no more than a single punctuation character or a pair of delimiting characters to express the few supported assertions. Over time, the expressiveness of regular expressions grew tremendously, but the syntax design was never revised and continues to rely on punctuation. As a result, regular expressions can be cryptic and extremely dense.