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Regular Expressions and You

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James Armes

This document discusses regular expressions and provides examples. It introduces regular expressions and their uses for validating email addresses. It then outlines the main types of regular expressions, including simple, POSIX basic, POSIX extended, and Perl regular expressions. POSIX basic regular expressions are described as creating a standard for Unix tools.

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Regular Expressions and You An introduction to regular expressions. James I. Armes Web Developer, AllPlayers.com @jamesiarmes
Email Validation Examples ^[w.%+-]+@[w.-]+.[A-Za-z]{2,4}$
Email Validation Examples (?:(?:rn)?[ t])*(?:(?:(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?: [^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[ ["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*|(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?: (?:rn)?[ t])*)*<(?:(?:rn)?[ t])*(?:@(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*(?:,@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+ (?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[ ["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*)*:(?:(?:rn)?[ t])*)?(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?: (?:rn)?[ t]))*"(?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?: (?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?: [^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*>(?:(?:rn)?[ t])*)|(?:[^()<>@,;:".[] 000-031]+(?:(?: (?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)*:(?:(?:rn)?[ t])*(?:(?:(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(? =[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?: [^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)? [ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*|(?:[^()<>@,;:".[] 000-031]+ (?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)*<(?:(?:rn)?[ t])*(?:@(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t]) +|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^ []r]|.)*](?:(?:rn)?[ t])*))*(?:,@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?: (?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*)*:(?:(?:rn)?[ t])*)?(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?: (?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[ ["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?: (?:rn)?[ t])*))*>(?:(?:rn)?[ t])*)(?:,s*(?:(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*) (?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?: [^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?: (?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*|(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?: (?:rn)?[ t]))*"(?:(?:rn)?[ t])*)*<(?:(?:rn)?[ t])*(?:@(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:. (?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*(?:,@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[ ["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*)*:(?:(?:rn)?[ t])*)?(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?: (?:rn)?[ t]))*"(?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?: (?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?: [^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*>(?:(?:rn)?[ t])*))*)?;s*)
Types of Regular Expressions ● Simple Regular Expressions ● POSIX Basic Regular Expressions ● POSIX Extended Regular Expressions ● Perl Regular Expressions
Simple Regular Expressions ● Traditional regular expressions. ● Not a standard. ● Support by some applications for backwards compatibility. ● Deprecated.
POSIX Basic Regular Expressions ● Created to provide a common standard for Unix tools. ● Designed to be backwards compatible with traditional regular expressions. ● Adopted as the default syntax of many Unix tools. ● Some metacharacters require escaping.
POSIX Extended Regular Expressions ● Adds some new metacharacters. ● Metacharacters do not require escaping. ● Dropped support for back references (n). ● Many Unix tools provide support with a command line argument (usually -E).
Perl Regular Expressions ● Adds lazy quantification, named capture groups and recursive patterns. ● Adopted by many programming languages due to its power. ● Requires non-alphanumeric delimiters around expression. ● Other languages only implement a subset, so implementations vary.
Syntax
Basic Metacharacters . Match any single character. ^ Matches beginning of a string. $ Matches end of a string. | Matches the expression before or after (think ||).
Character Classes [] Match any characters within the group. [^ ] Match any characters NOT within the group. [n-m] Match a range of characters. Examples: [A-Za-z0-9] [^G-Zg-z _]
Shorthand Character Classes s Any whitespace character such as space, tab and newlines. Same as [nrt ] w Any word character. Same as [A-Za-z0-9_] d Any digit character. Same as [0-9] S, W, D Negated version of the above. Can be used inside character classes but could be confusing.
Quantifiers * Match the preceding expression 0 or more times. + Match the preceding expression 1 or more times. ? Match the preceding expression 0 or 1 time. {m,n} Match the preceding expression at least m times but no more than n times. {m,} Match the preceding expression at least m times with no maximum. {,n} Match the preceding expression no more than n times with no minimum. {n} Match the preceding expression exactly n times.
Lazy Quantifiers Standard Quantifiers are greedy. Example: Many programming courses start with a "Hello World" example. That would be "Hallo Welt" in German. "Hello .*" Many programming courses start with a "Hello World" example. That would be "Hallo Welt" in German.
Lazy Quantifiers Use ? to make a quantifier lazy. Example: Many programming courses start with a "Hello World" example. That would be "Hallo Welt" in German. "Hello .*?" Many programming courses start with a "Hello World" example. That would be "Hallo Welt" in German.
Grouping () Group the expression and capture the text. (?: ) Group the expression but DO NOT capture the text.
Backreferences 1 through 9 reference previously captured text. Example: Many programming courses start with a "Hello World" example. 'Hello World' examples are extremely simple, especially when they just output "Hello World'. ('|")Hello World(1) Many programming courses start with a "Hello World" example. 'Hello World' examples are extremely simple, especially when they just output "Hello World'.
Word Boundaries b matches the position between a word character (w) and a non-word character (W). Example: Hello World ob Hello| World
Word Boundaries B matches the position between two word characters (ww). Example: Hello World oB Hello Wo|rld
Lookaheads (?= ) matches the position directly before the expression is matched. Example: Hello World sounds better than "Hello Earth". Hello(?= World) Hello World sounds better than "Hello Earth".
Lookbehinds (?<= ) matches the position directly after the expression is matched. Example: Hello World sounds better than "Hello Earth". (?<=")Hello Hello World sounds better than "Hello Earth".
Lookaheads (?! ) matches the position directly before the expression is NOT matched. Example: Hello World sounds better than "Hello Earth". Hello(?! World) Hello World sounds better than "Hello Earth".
Lookbehinds (?<! ) matches the position directly after the expression is NOT matched. Example: Hello World sounds better than "Hello Earth". (?<!")Hello Hello World sounds better than "Hello Earth".
Conditionals (?(condition)then|else) ● condition must be a lookahead or a lookbehind. ● If condition is matched, then must match for the expression to pass. ● If condition is not matched, else must match for the expression to pass.
Conditionals Example: Hello World sounds better than "Hello Earth". Hello (?(?<=World)World|Earth) Hello World sounds better than "Hello Earth". Hello (?(?<=People)People|Earth) Hello World sounds better than "Hello Earth".
Modifiers i Case insensitive matching. s . matches newline characters. m ^ and $ match after and before newlines (respectively). x Whitespace within the expression is ignored unless escaped. g Match globally.
Modifiers ● (?a) to turn modifiers on. ●(?-a) to turn modifiers off. Examples: (?i)WORLD(?-i) (?i-s)WORLD.(?s-i) (?i:WORLD)
Language Implementations
JavaScript ● RegExp object. – var expression = new RegExp('World', 'g'); – var expression = /World/g; ● String.match() ● String.replace() ● String.split()
Perl ● if ($string =~ /regex/) ● $string =~ s/regex/replacement/ ● Regexp::Common – http://search.cpan.org/dist/Regexp-Common/ – Provides common expressions. – Examples: ● IP Address ● Credit Card Number ● Profanity
PHP ● ereg vs. preg – preg uses Perl syntax. – ereg uses POSIX Extended syntax. – preg is much faster. – ereg has been deprecated as of PHP 5.3.
PHP ● preg_match() ● preg_match_all() ● preg_replace() ● preg_split() ● preg_quote() ● http://www.php.net/manual/en/book.pcre.php ● http://php.net/manual/reference.pcre.pattern.modifiers.php
Tools and Resources ● txt2regex - http://aurelio.net/txt2regex/ ● Reggy (mac) - http://reggyapp.com/ ● Patterns (mac) - http://krillapps.com/patterns/ ● Web based - http://regex.larsolavtorvik.com/ ● Regular-Expressions.info (reference) - http://www.regular-expressions.info/
Thanks! http://xkcd.com/208/

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Regular Expressions and You

  • 1. Regular Expressions and You An introduction to regular expressions. James I. Armes Web Developer, AllPlayers.com @jamesiarmes
  • 2. Email Validation Examples ^[w.%+-]+@[w.-]+.[A-Za-z]{2,4}$
  • 3. Email Validation Examples (?:(?:rn)?[ t])*(?:(?:(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?: [^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[ ["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*|(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?: (?:rn)?[ t])*)*<(?:(?:rn)?[ t])*(?:@(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*(?:,@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+ (?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[ ["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*)*:(?:(?:rn)?[ t])*)?(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?: (?:rn)?[ t]))*"(?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?: (?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?: [^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*>(?:(?:rn)?[ t])*)|(?:[^()<>@,;:".[] 000-031]+(?:(?: (?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)*:(?:(?:rn)?[ t])*(?:(?:(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(? =[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?: [^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)? [ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*|(?:[^()<>@,;:".[] 000-031]+ (?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)*<(?:(?:rn)?[ t])*(?:@(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t]) +|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^ []r]|.)*](?:(?:rn)?[ t])*))*(?:,@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?: (?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*)*:(?:(?:rn)?[ t])*)?(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?: (?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[ ["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?: (?:rn)?[ t])*))*>(?:(?:rn)?[ t])*)(?:,s*(?:(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*) (?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?: [^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?: (?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*|(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?: (?:rn)?[ t]))*"(?:(?:rn)?[ t])*)*<(?:(?:rn)?[ t])*(?:@(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:. (?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*(?:,@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[ ["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*)*:(?:(?:rn)?[ t])*)?(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?: (?:rn)?[ t]))*"(?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?: (?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?: [^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*>(?:(?:rn)?[ t])*))*)?;s*)
  • 4. Types of Regular Expressions ● Simple Regular Expressions ● POSIX Basic Regular Expressions ● POSIX Extended Regular Expressions ● Perl Regular Expressions
  • 5. Simple Regular Expressions ● Traditional regular expressions. ● Not a standard. ● Support by some applications for backwards compatibility. ● Deprecated.
  • 6. POSIX Basic Regular Expressions ● Created to provide a common standard for Unix tools. ● Designed to be backwards compatible with traditional regular expressions. ● Adopted as the default syntax of many Unix tools. ● Some metacharacters require escaping.
  • 7. POSIX Extended Regular Expressions ● Adds some new metacharacters. ● Metacharacters do not require escaping. ● Dropped support for back references (n). ● Many Unix tools provide support with a command line argument (usually -E).
  • 8. Perl Regular Expressions ● Adds lazy quantification, named capture groups and recursive patterns. ● Adopted by many programming languages due to its power. ● Requires non-alphanumeric delimiters around expression. ● Other languages only implement a subset, so implementations vary.
  • 10. Basic Metacharacters . Match any single character. ^ Matches beginning of a string. $ Matches end of a string. | Matches the expression before or after (think ||).
  • 11. Character Classes [] Match any characters within the group. [^ ] Match any characters NOT within the group. [n-m] Match a range of characters. Examples: [A-Za-z0-9] [^G-Zg-z _]
  • 12. Shorthand Character Classes s Any whitespace character such as space, tab and newlines. Same as [nrt ] w Any word character. Same as [A-Za-z0-9_] d Any digit character. Same as [0-9] S, W, D Negated version of the above. Can be used inside character classes but could be confusing.
  • 13. Quantifiers * Match the preceding expression 0 or more times. + Match the preceding expression 1 or more times. ? Match the preceding expression 0 or 1 time. {m,n} Match the preceding expression at least m times but no more than n times. {m,} Match the preceding expression at least m times with no maximum. {,n} Match the preceding expression no more than n times with no minimum. {n} Match the preceding expression exactly n times.
  • 14. Lazy Quantifiers Standard Quantifiers are greedy. Example: Many programming courses start with a "Hello World" example. That would be "Hallo Welt" in German. "Hello .*" Many programming courses start with a "Hello World" example. That would be "Hallo Welt" in German.
  • 15. Lazy Quantifiers Use ? to make a quantifier lazy. Example: Many programming courses start with a "Hello World" example. That would be "Hallo Welt" in German. "Hello .*?" Many programming courses start with a "Hello World" example. That would be "Hallo Welt" in German.
  • 16. Grouping () Group the expression and capture the text. (?: ) Group the expression but DO NOT capture the text.
  • 17. Backreferences 1 through 9 reference previously captured text. Example: Many programming courses start with a "Hello World" example. 'Hello World' examples are extremely simple, especially when they just output "Hello World'. ('|")Hello World(1) Many programming courses start with a "Hello World" example. 'Hello World' examples are extremely simple, especially when they just output "Hello World'.
  • 18. Word Boundaries b matches the position between a word character (w) and a non-word character (W). Example: Hello World ob Hello| World
  • 19. Word Boundaries B matches the position between two word characters (ww). Example: Hello World oB Hello Wo|rld
  • 20. Lookaheads (?= ) matches the position directly before the expression is matched. Example: Hello World sounds better than "Hello Earth". Hello(?= World) Hello World sounds better than "Hello Earth".
  • 21. Lookbehinds (?<= ) matches the position directly after the expression is matched. Example: Hello World sounds better than "Hello Earth". (?<=")Hello Hello World sounds better than "Hello Earth".
  • 22. Lookaheads (?! ) matches the position directly before the expression is NOT matched. Example: Hello World sounds better than "Hello Earth". Hello(?! World) Hello World sounds better than "Hello Earth".
  • 23. Lookbehinds (?<! ) matches the position directly after the expression is NOT matched. Example: Hello World sounds better than "Hello Earth". (?<!")Hello Hello World sounds better than "Hello Earth".
  • 24. Conditionals (?(condition)then|else) ● condition must be a lookahead or a lookbehind. ● If condition is matched, then must match for the expression to pass. ● If condition is not matched, else must match for the expression to pass.
  • 25. Conditionals Example: Hello World sounds better than "Hello Earth". Hello (?(?<=World)World|Earth) Hello World sounds better than "Hello Earth". Hello (?(?<=People)People|Earth) Hello World sounds better than "Hello Earth".
  • 26. Modifiers i Case insensitive matching. s . matches newline characters. m ^ and $ match after and before newlines (respectively). x Whitespace within the expression is ignored unless escaped. g Match globally.
  • 27. Modifiers ● (?a) to turn modifiers on. ●(?-a) to turn modifiers off. Examples: (?i)WORLD(?-i) (?i-s)WORLD.(?s-i) (?i:WORLD)
  • 29. JavaScript ● RegExp object. – var expression = new RegExp('World', 'g'); – var expression = /World/g; ● String.match() ● String.replace() ● String.split()
  • 30. Perl ● if ($string =~ /regex/) ● $string =~ s/regex/replacement/ ● Regexp::Common – http://search.cpan.org/dist/Regexp-Common/ – Provides common expressions. – Examples: ● IP Address ● Credit Card Number ● Profanity
  • 31. PHP ● ereg vs. preg – preg uses Perl syntax. – ereg uses POSIX Extended syntax. – preg is much faster. – ereg has been deprecated as of PHP 5.3.
  • 32. PHP ● preg_match() ● preg_match_all() ● preg_replace() ● preg_split() ● preg_quote() ● http://www.php.net/manual/en/book.pcre.php ● http://php.net/manual/reference.pcre.pattern.modifiers.php
  • 33. Tools and Resources ● txt2regex - http://aurelio.net/txt2regex/ ● Reggy (mac) - http://reggyapp.com/ ● Patterns (mac) - http://krillapps.com/patterns/ ● Web based - http://regex.larsolavtorvik.com/ ● Regular-Expressions.info (reference) - http://www.regular-expressions.info/