The document provides an overview of regular expressions (regex), explaining their role in matching and manipulating textual data. It covers key concepts such as literals, anchors, character classes, alternation, quantifiers, grouping, and delimiters, along with examples of usage in PHP. Additionally, it illustrates how to perform matches and replacements using various regex functions.

1. Regular Expression Basics PHPNW 2008 Ciarán Walsh

2. What are regular expressions? Regular expressions allow matching and manipulation of textual data. Abbreviated as regex or regexp , or alternatively just “patterns”.

3. Regular Expression Basics Literals bus Matches a ‘ b ’, followed by a ‘ u ’, followed by an ‘ s ’

4. Regular Expression Basics Anchors ^ Matches at the beginning of a line $ Matches at the end of a line

5. Regular Expression Basics Character Classes [abc] Matches one of ‘ a ’, ‘ b ’ or ‘ c ’ [a-c] Same as above (character range) [^abc] Matches one character that is not listed . Matches any single character

6. Regular Expression Basics Alternation a|b Matches one of ‘ a ’ or ‘ b ’ dog|cat Matches one of “dog” or “cat”

7. Regular Expression Basics Quantifiers (repetition) {x,y} Matches minimum of x and a maximum of y occurrences; either can be omitted * Matches zero or more occurrences (any amount). Same as {0,} + Matches one or more occurrences. Same as {1,} ? Matches zero or one occurrences. Same as {0,1}

8. Regular Expression Basics Grouping (…) Groups the contents of the parentheses. Affects alternation and quantifiers. Allows parts of the match to be captured for|backward “ for” or “backward” (for|back)ward “ forward” or “backward”

9. Regular Expression Basics Delimiters pattern / modifiers / /i Makes match case-insensitive

10. Performing a Match Returns number of matches (0 or 1) $matches will contain captured groups preg_match ( '/Te(.)f?/i' , 'text' , $ matches );

11. Performing a Replacement Returns string after replacement Can use backreferences with \0-9 preg_replace ( '/some(text)/' , '\1' , $ text )

12. (?:(?:\r\n)?[ \t])*(?:(?:(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|&quot;(?:[^\&quot;\r\\]|\\.|(?:(?:\r\n)?[ \t]))*&quot;(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?: (?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|&quot;(?:[^\&quot;\r\\]|\\.|(?:(?:\r\n)?[ \t]))*&quot;(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\ ]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*|(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n )?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|&quot;(?:[^\&quot;\r\\]|\\.|(?:(?:\r\n)?[ \t]))*&quot;(?:(?:\r\n)?[ \t])*)*\<(?:(?:\r\n)?[ \t])*(?:@(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.) *\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*(?:,@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\0 31]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\ ](?:(?:\r\n)?[ \t])*))*)*:(?:(?:\r\n)?[ \t])*)?(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|&quot;(?:[^\&quot;\r\\]|\\.|(?:(?:\r\n)?[ \t]))*&quot;(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\ \&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|&quot;(?:[^\&quot;\r\\]|\\.|(?:(?:\r\n)?[ \t]))*&quot;(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot; .\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*\>(?:(?:\r\n)?[ \t])*)|(? :[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|&quot;(?:[^\&quot;\r\\]|\\.|(?:(?:\r\n)?[ \t]))*&quot;(?:(?:\r\n)?[ \t])*)*:(?:(?:\r\n)?[ \t])*(?:(?:(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|( ?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|&quot;(?:[^\&quot;\r\\]|\\.|(?:(?:\r\n)?[ \t]))*&quot;(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|&quot;(?:[^\&quot;\r\\]|\\.|(?:(?:\r\n)?[ \t] ))*&quot;(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031] +(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*|(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|&quot;(?:[^\&quot;\r\\]|\\.|(?:(?:\r\n)?[ \t]))*&quot;(?:(?: \r\n)?[ \t])*)*\<(?:(?:\r\n)?[ \t])*(?:@(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(? :(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*(?:,@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?: \r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*)*:(?:(?:\r\n)?[ \t])*)?(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(? :(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|&quot;(?:[^\&quot;\r\\]|\\.|(?:(?:\r\n)?[ \t]))*&quot;(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|&quot;(?:[^\&quot;\r\\] |\\.|(?:(?:\r\n)?[ \t]))*&quot;(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@ ,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*\>(?:(?:\r\n)?[ \t])*)(?:,\s*(?:(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;. \[\]]))|&quot;(?:[^\&quot;\r\\]|\\.|(?:(?:\r\n)?[ \t]))*&quot;(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|&quot;(?:[^\&quot;\r\\]|\\.|(?:(?:\r\n)?[ \t]))*&quot;(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*|(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|&quot;(?:[^\&quot;\r\\]|\\.|(?:(?:\r\n)?[ \t]))*&quot;(?:(?:\r\n)?[ \t])*)*\<( ?:(?:\r\n)?[ \t])*(?:@(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+| \Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*(?:,@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\ .(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*)*:(?:(?:\r\n)?[ \t])*)?(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+| \Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|&quot;(?:[^\&quot;\r\\]|\\.|(?:(?:\r\n)?[ \t]))*&quot;(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|&quot;(?:[^\&quot;\r\\]|\\.|(?:(?:\r\n)?[ \t]))*&quot;(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\&quot;.\[\] \000-\ 031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[&quot;()<>@,;:\\&quot;.\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*\>(?:(?:\r\n)?[ \t])*))*)?;\s*) Don’t Use Regular Expressions! Don’t Abuse Regular Expressions! Some people, when confronted with a problem, think “ I know, I'll use regular expressions.” Now they have two problems. — Jamie Zawinski

13. Testing for a Substring if ( preg_match ( '/foo/' , $ var )) if ( strpos ( $ var , 'foo' ) !== false ) if ( preg_match ( '/foo/i' , $ var )) if ( stripos ( $ var , 'foo' ) !== false )

14. Validating an Integer Intention is not immediately obvious Not efficient if ( preg_match ( '/ ^ \d +$ /' , $ value )) { // $value is a positive integer } Regular Expression

15. Validating an Integer Native C library (fast) Makes the intention obvious ctype (Character Type) if ( ctype_digit ( $ value )) { // $value is a positive integer }

16. Validating an Integer Intention is fairly clear Casting is safe practice Any invalid values will result in zero $ casted_value = intval ( $ value ); if ( $ casted_value > 0 ) { // $casted_value is a positive (non-zero) integer } Casting

17. HTML Parsing

18. Using Regular Expressions

19. Using Regular Expressions Postcodes /[A-Z]{1,2}[0-9R][0-9A-Z]? [0-9][A-Z]{2}/ IP Addresses @^(\d{1,2})/(\d{1,2})/(\d{4})$@

20. Constructing Patterns Writing patterns is a balance between matching what you do want, against not matching what you don’t want.

21. You don’t need to use /…/ to denote a pattern! /…/ to denote a pattern! preg_match ( '/<b><s> .+ < \/ s> .+ < \/ b>/' , $ html ) preg_match ( '@<b><s> .+ </s> .+ </b>@' , $ html )

22. Greediness $ html = <<< HTML <span> some text </span><span> some more text! </span> HTML ; preg_match ( &quot;@<span>(.+)</span>@&quot; , $ html , $ matches ); echo $ matches [ 0 ]; preg_match ( &quot;@<span>(.+?)</span>@&quot; , $ html , $ matches ); echo $ matches [ 0 ];

23. You can make your pattern readable! preg_match ( '`^(\w+)://(?:(.+?):(.+?)@)?(.+?)\.(\w+)$`' , $ s , $ matches ) preg_match ( '` ^ (\w+):// # Protocol (?: (.+?) # Username : # : (.+?) # Password @ # @ )? # Username/password are optional (.+?) # Hostname \.(\w+) # Top-level domain $ `x' , $ s , $ matches );

24. Extracting Captures preg_match ( '`^ (?P<protocol>\w+):// (?: (?P<user>.+?) : (?P<pass>.+?) @ )? (?P<host>.+?) \.(?P<tld>\w+) $`x' , $ s , $ matches ); Array( [0] => http://foo:bar@baz.example.com [protocol] => http [1] => http [user] => foo [2] => foo [pass] => bar [3] => bar [host] => baz.example [4] => baz.example [tld] => com [5] => com) preg_match ( '`^ (?P<protocol>\w+):// (?: (?P<user>.+?) : (?P<pass>.+?) @ )? (?P<host>.+?) \.(?P<tld>\w+) $`x' , $ s , $ matches );

25. Variable Data if ( preg_match ( &quot;!> $ value </(?:div|span)>!&quot; , $ text )) $ value = preg_quote ( $ value , '!' );

26. Performing Logic on Replacements preg_replace ( '/\w + /e' , 'strtoupper(&quot;\0&quot;)' , 'foo bar baz' ) function upper_case_match ( $ matches ) { return strtoupper ( $ matches [ 0 ]); } preg_replace_callback ( '/\w + /' , 'upper_case_match' , 'foo bar baz' )

27. Testing Tools RegexBuddy Reggy http://rubular.com

28. Any Questions?