Regular Expression Basics PHPNW 2008 Ciarán Walsh

PHPNW 2008

Ciarán Walsh

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

Regular expressions allow matching and manipulation of textual data.

Abbreviated as regex or regexp , or alternatively just “patterns”.

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

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

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

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

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}

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”

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

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

Returns number of matches (0 or 1)

$matches will contain captured groups

preg_match (

'/Te(.)f?/i' ,

'text' ,

$ matches

);

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

Returns string after replacement

Can use backreferences with -9

preg_replace (

'/some(text)/' ,

'1' ,

$ text

)

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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 )

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

Intention is not immediately obvious

Not efficient

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

Native C library (fast)

Makes the intention obvious

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

Intention is fairly clear

Casting is safe practice

Any invalid values will result in zero

HTML Parsing

Using Regular Expressions

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})$@

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

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

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 )

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 ];

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 );

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 );

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

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

function upper_case_match ( $ matches ) {

return strtoupper ( $ matches [ 0 ]);

}

preg_replace_callback (

'/w + /' ,

'upper_case_match' ,

'foo bar baz'

)

Testing Tools RegexBuddy Reggy http://rubular.com

RegexBuddy

Reggy

http://rubular.com

Any Questions?