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Regular expressions and php

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David Stockton

The document discusses regular expressions (regex) in PHP. It begins with a brief introduction to regex, then provides examples of common PHP functions for using regex like preg_match(), preg_replace(), and preg_quote(). The document also shares a very long regex pattern that is intended to match all valid email addresses. It notes that accurately matching email addresses with a regex is challenging.

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Regular Expressions in PHP/(?:dave@davidstockton\.com)/Front Range PHP User GroupDavid Stockton
What is a regular expression?A pattern used to describe a part of some text“Regular” has some implications to how it can be built, but that’s not really part of this presentationExtremely powerful and useful(And often abused)
Regex JokeA programmer says, “I have a problem that I can solve with regular expressions.”Now, he has two problems…
How to use regex in PHP The preg_* functionsPerl compatible regular expressions.Probably the most common regex syntaxThe ereg_* functionsPOSIX style regular expressionsI am not covering these functions.Don’t use the ereg ones. They are deprecated in PHP 5.3.
How can we use regex in PHP?preg_match( ) – Searches a subject for a matchpreg_match_all( ) – Searches a subject for all matchespreg_replace( ) – Searches a subject for a pattern and replaces it with something elsepreg_split( ) – Split a string into an array based on a regex delimiterpreg_filter( ) – Identical to preg_replace except it returns only the matchespreg_replace_callback( ) – Like preg_replace, but replacement is defined in a callbackpreg_grep( ) – Returns an array of array elements that match a pattern
How can we use regex in PHP?preg_quote( ) – Quotes regular expression characterspreg_last_error( ) – Returns the error code of the last PCRE (Perl Compatible Regular Expression) function execution
How can we use regex in PHP?Those are the function calls, and we’ll play with the later.First, we need to learn how to create regex patterns since we need those for any function call.
Starting Pattern/[A-Z0-9\._+=]+@[A-Z0-9\.-]\.[A-Z]{2,4}/iThis matches a series of letters, numbers, plus, dash, dots, underscores and equals, followed by an “AT” (@) sign, followed by a series of letters, numbers, dots and dashes, followed by a dot, followed by 2 to 4 letters.In other words… It matches an email address… Or rather some email addresses.
Matching Email AddressesWhat about james@smithsonian.museum?What about freddie@wherecanI.travel?Both of those are valid email addresses, but they fail because our patter only allows 2-4 character TLD parts for the email address.How can we match all valid email addresses and only valid email addresses?
The “real” email address regex(?:(?:\r\n)?[ \t])*(?:(?:(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t] )+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?: \r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:( ?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\0 31]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\ ](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+ (?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?: (?:\r\n)?[ \t])*))*|(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z |(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n) ?[ \t])*)*\<(?:(?:\r\n)?[ \t])*(?:@(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\ r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n) ?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t] )*))*(?:,@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])* )(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t] )+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*) *:(?:(?:\r\n)?[ \t])*)?(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+ |\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r \n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?: \r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t ]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031 ]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\]( ?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(? :(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(? :\r\n)?[ \t])*))*\>(?:(?:\r\n)?[ \t])*)|(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(? :(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)? [ \t]))*"(?:(?:\r\n)?[ \t])*)*:(?:(?:\r\n)?[ \t])*(?:(?:(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]| \\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<> @,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|" (?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t] )*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\ ".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(? :[^()<>@,;:\\".\[\] \000-
The “real” email address regex cont.\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[ \]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*|(?:[^()<>@,;:\\".\[\] \000- \031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|( ?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)*\<(?:(?:\r\n)?[ \t])*(?:@(?:[^()<>@,; :\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([ ^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\" .\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\ ]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*(?:,@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\ [\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\ r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\] |\\.)*\](?:(?:\r\n)?[ \t])*))*)*:(?:(?:\r\n)?[ \t])*)?(?:[^()<>@,;:\\".\[\] \0 00-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\ .|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@, ;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(? :[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])* (?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\". \[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[ ^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\] ]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*\>(?:(?:\r\n)?[ \t])*)(?:,\s*( ?:(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\ ".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:( ?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[ \["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t ])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t ])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(? :\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+| \Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*|(?: [^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\ ]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)*\<(?:(?:\r\n) ?[ \t])*(?:@(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[" ()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n) ?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<> @,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*(?:,@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@, ;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t] )*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\ ".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*)*:(?:(?:\r\n)?[ \t])*)? (?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\". \[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:(?: \r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[ "()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t]) *))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t]) +|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\ .(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z |(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*\>(?:( ?:\r\n)?[ \t])*))*)?;\s*)
So… How do we write this?Don’t. Other much more simple patterns have been written and will match 99.9% of valid email addresses.Use something like Zend_Validate_EmailAddress
So now the real learnin’…Letters and numbers match… letters and numbers/a/ - Matches a string that contains an “a”/7/ - Matches a string that contains a 7.
More learnin’Match a word/regex/ - Matches a string with the word “regex” in itYou can use a pipe character to give a choice/pizza|steak|cheeseburger/ - Matches a string with any of these foods
DelimitersThe examples so far have started with / and ended with /.These are delimiters and let the regex engine know where the pattern starts and ends.You can choose another delimiter if you’d like or if it’s more convenientMatch namespace:#/My/PHP/Namespace#If I used “/” in that example, I’d need to escape each of the forward slashes to differentiate them from the delimiter
Character Matching ContinuedYou can match a selection of characters/[Pp][Hh][Pp]/ - Matches PHP in any mixture of upper and lowercaseRanges can be defined/[abcdefghijklmnopqrstuvwxyz]/ - Matches any lowercase alpha character/[a-z]/ - Matches any lowercase alpha character
Character Selection RangesRanges can be combined/[A-Za-z0-9]/ - Matches an alphanumeric character/[A-Fa-f0-9]/ - Matches any hex characterCharacter Selection can be inversed/[^0-9]/ - Matches any non-digit character/[^ ]/ - Matches any non space character/[.!@#$%^*]/ - Matches some punctuation
Special CharactersDot (.) matches any character/.//../ - Matches any two charactersTo match an actual dot character, you must escape/\./ - Matches a single dot characterUnless it’s a character selection/[.]/ - Matches a single dot character
Character classes\d means [0-9]\D means non-digits - [^0-9]\w means word characters - [A-Za-z0-9_]\W means non word characters – [^A-Za-z0-9_]\s means a whitespace character [ \t\n\r]\S means non white space characters
Repeating Character ClassesMatch two digits in a row/\d\d//[0-9][0-9]//\d{2}//[0-9]{2}/Match at least one digit (but as many as it can)/\d+/Match 0 to infinite digits/\d*/
Repeating Character Classes cont.* means match 0 or more+ means match 1 or more{x} where x is a number means match exactly x of the preceding selection{x,} means match at least x{x,y} means match between x and y{,y} means match up to y
More special characters? Means the preceding selection is optionalPutting it togetherTelephone Number/\(?(\d{3})\)?[\s-]?(\d{3})[\s-]?(\d{4})/Matches 720-675-7471 or (720)675-7471 or (720) 675-7471 or 7206757471 or 720 675 7471Find a misspelled word (and get great deals on EBay)/la[bp]topcomputer[s]?/
Regex AnchorsAnchors allow you to specify a position, like before, after or in between characters/^ab/ matches abcdefg but not cabNotice that it’s the caret character… It means start of the string in this context, but means the opposite of a character class inside the square brackets/ab$/ matches cab but not abcdefg/^[a-z]+$/ will match a string that consists only of lowercase characters
Word Boundaries\b means word boundariesBefore first character if first character is a word characterAfter last character if last character is a word characterBetween two characters if one is a word character and the other is not/\bfish\b/ matches fish, but not fisherman or catfish./fish\b/ matches fish and catfish
Alternation/cow|boy/ - Matches cow, or boy or cowboy or coward, etc/\b(cow|boy)\b/ - Matches cow or boy but not cowboy or cowardThe above example also captures the matching word due to the parens. More on this later.
Greedy vs LazyBy default, regular expressions are greedy… That is, they will match as much as they canGrab a starting html tag:/<.+>/ Matches in bold: <h1>Welcome to FRPUG</h1>Not what we wantMake it lazy: /<.+?>/Now it matches <h1>Welcome to FRPUG</h1>
Another tag matching solution/<[^>]+>/Literally match a less than character followed by one or more non-greater than characters followed by a greater than characterThis way eliminates the need for the engine to backtrack (almost certainly faster than the last example).
Capturing part of regex (backreference)/__(construct|destruct)/Backreference will contain either construct or destruct so you can use it later/([a-z]+)\1/Matches groups of repeated characters that repeat an even number of times.Matches aa but not a. Matches aaaaa/([a-z]{3})\1/Matches words like booboo or bambam
Backreference Continued…Very useful when performing regex search and replacepreg_replace('/\(?(\d{3})\)?[\s-]?(\d{3})[\s-]?(\d{4})/', '(\1) \2-\3', $phone)The above example will take any phone number from the previous example and return it formatted in (xxx) xxx-xxxx format
More backreferences…Replace duplicated words that that have been inadvertently left in
Non-capturing groupsMatch an IPv4 address/((?:\d{1,3}\.){3}\d{1,3})/We’re matching 1 to 3 digits followed by a dot 3 times. We don’t care (right now) about the octets, we just want to repeat the match, so ?: says to not capture the group.
Pattern Modifiers Modifiers go after the last delimiter (now you know why there are delimiters) and affect how the regex engine worksi – case insensitive matching (matches are case-sensitive by default)m – multiline matchings - dot matches all characters, including \nx – ignore all whitespace characters except if escaped or in a character class
Pattern Modifiers Continued…D – Anchor for the end of the string only, otherwise $ matches \n charactersAllow username to be alphabetic only/^[A-Za-z]$/ - This will match dave\nextra stuffHowever, /^[A-Za-z]$/D will not matchU – Invert the meaning of the greediness. With this on by default matches are lazy and ? makes it greedy.There are lots of other modifiers and you can see them at http://us2.php.net/manual/en/reference.pcre.pattern.modifiers.php
Named Capture GroupsRather than get back a numbered array of matches, get back an associative array.If you add a new capture group, you don’t have to renumber where you use the capture group
Named Capture Groups cont…Use (?P<named_group>pattern)
Named Capture Groups cont…Combined numbered and associative arrayCapture group 0 is the wholepattern that is matched.If our string to match against was abcde720-675 7471foobar, $matches[0] will contain720-675 7471
Positive Look Ahead MatchesLook for a pattern follow by another pattern/p(?=h)/ - Match a “p” followed by an “h” but don’t include the “h”
Negative Look AheadLook for a pattern which is not followed by some other pattern/p(?=!h)/ - pnot followed by h.
Look AheadsPositive and negative look aheads do not capture anything. They just determine if the pattern match is possibleThey are zero-width/p[^h]/ is not the same as /p(?!h)//ph/ is not the same as /p(?=h)/
Look behindsPositive look behind/(?<=oo)d/ - d which is preceded by ooMatches “food”, “mood”, match only contains the “d”Negative look behind/(?<!oo)d/ - d which is not preceded by ooMatches “dude”, “crude”, and “d”
With great power…Test your regular expressions before they go to productionIt’s much easier to get them wrong than to get themright if you don’t test
When to not use regexWhenever they aren’t needed.If you can use strstr or strpos or str_replace to do the job, do that. They are much faster, much simpler and easier to do correctly.However, if you cannot use those functions, regex may be your best bet.Don’t use regex when you really need a parser
Resourceshttp://regular-expressions.infohttp://us2.php.net/manual/en/ref.pcre.phpSpider Man from http://www.onlineseats.com/
Questions?dave@frontrangephp.org

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Regular expressions and php

  • 1. Regular Expressions in PHP/(?:dave@davidstockton\.com)/Front Range PHP User GroupDavid Stockton
  • 2. What is a regular expression?A pattern used to describe a part of some text“Regular” has some implications to how it can be built, but that’s not really part of this presentationExtremely powerful and useful(And often abused)
  • 3. Regex JokeA programmer says, “I have a problem that I can solve with regular expressions.”Now, he has two problems…
  • 4. How to use regex in PHP The preg_* functionsPerl compatible regular expressions.Probably the most common regex syntaxThe ereg_* functionsPOSIX style regular expressionsI am not covering these functions.Don’t use the ereg ones. They are deprecated in PHP 5.3.
  • 5. How can we use regex in PHP?preg_match( ) – Searches a subject for a matchpreg_match_all( ) – Searches a subject for all matchespreg_replace( ) – Searches a subject for a pattern and replaces it with something elsepreg_split( ) – Split a string into an array based on a regex delimiterpreg_filter( ) – Identical to preg_replace except it returns only the matchespreg_replace_callback( ) – Like preg_replace, but replacement is defined in a callbackpreg_grep( ) – Returns an array of array elements that match a pattern
  • 6. How can we use regex in PHP?preg_quote( ) – Quotes regular expression characterspreg_last_error( ) – Returns the error code of the last PCRE (Perl Compatible Regular Expression) function execution
  • 7. How can we use regex in PHP?Those are the function calls, and we’ll play with the later.First, we need to learn how to create regex patterns since we need those for any function call.
  • 8. Starting Pattern/[A-Z0-9\._+=]+@[A-Z0-9\.-]\.[A-Z]{2,4}/iThis matches a series of letters, numbers, plus, dash, dots, underscores and equals, followed by an “AT” (@) sign, followed by a series of letters, numbers, dots and dashes, followed by a dot, followed by 2 to 4 letters.In other words… It matches an email address… Or rather some email addresses.
  • 9. Matching Email AddressesWhat about [email protected]?What about [email protected]?Both of those are valid email addresses, but they fail because our patter only allows 2-4 character TLD parts for the email address.How can we match all valid email addresses and only valid email addresses?
  • 10. The “real” email address regex(?:(?:\r\n)?[ \t])*(?:(?:(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t] )+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?: \r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:( ?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\0 31]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\ ](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+ (?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?: (?:\r\n)?[ \t])*))*|(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z |(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n) ?[ \t])*)*\<(?:(?:\r\n)?[ \t])*(?:@(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\ r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n) ?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t] )*))*(?:,@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])* )(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t] )+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*) *:(?:(?:\r\n)?[ \t])*)?(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+ |\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r \n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?: \r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t ]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031 ]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\]( ?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(? :(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(? :\r\n)?[ \t])*))*\>(?:(?:\r\n)?[ \t])*)|(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(? :(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)? [ \t]))*"(?:(?:\r\n)?[ \t])*)*:(?:(?:\r\n)?[ \t])*(?:(?:(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]| \\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<> @,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|" (?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t] )*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\ ".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(? :[^()<>@,;:\\".\[\] \000-
  • 11. The “real” email address regex cont.\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[ \]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*|(?:[^()<>@,;:\\".\[\] \000- \031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|( ?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)*\<(?:(?:\r\n)?[ \t])*(?:@(?:[^()<>@,; :\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([ ^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\" .\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\ ]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*(?:,@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\ [\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\ r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\] |\\.)*\](?:(?:\r\n)?[ \t])*))*)*:(?:(?:\r\n)?[ \t])*)?(?:[^()<>@,;:\\".\[\] \0 00-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\ .|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@, ;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(? :[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])* (?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\". \[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[ ^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\] ]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*\>(?:(?:\r\n)?[ \t])*)(?:,\s*( ?:(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\ ".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:( ?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[ \["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t ])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t ])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(? :\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+| \Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*|(?: [^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\ ]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)*\<(?:(?:\r\n) ?[ \t])*(?:@(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[" ()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n) ?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<> @,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*(?:,@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@, ;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t] )*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\ ".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*)*:(?:(?:\r\n)?[ \t])*)? (?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\". \[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:(?: \r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[ "()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t]) *))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t]) +|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\ .(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z |(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*\>(?:( ?:\r\n)?[ \t])*))*)?;\s*)
  • 12. So… How do we write this?Don’t. Other much more simple patterns have been written and will match 99.9% of valid email addresses.Use something like Zend_Validate_EmailAddress
  • 13. So now the real learnin’…Letters and numbers match… letters and numbers/a/ - Matches a string that contains an “a”/7/ - Matches a string that contains a 7.
  • 14. More learnin’Match a word/regex/ - Matches a string with the word “regex” in itYou can use a pipe character to give a choice/pizza|steak|cheeseburger/ - Matches a string with any of these foods
  • 15. DelimitersThe examples so far have started with / and ended with /.These are delimiters and let the regex engine know where the pattern starts and ends.You can choose another delimiter if you’d like or if it’s more convenientMatch namespace:#/My/PHP/Namespace#If I used “/” in that example, I’d need to escape each of the forward slashes to differentiate them from the delimiter
  • 16. Character Matching ContinuedYou can match a selection of characters/[Pp][Hh][Pp]/ - Matches PHP in any mixture of upper and lowercaseRanges can be defined/[abcdefghijklmnopqrstuvwxyz]/ - Matches any lowercase alpha character/[a-z]/ - Matches any lowercase alpha character
  • 17. Character Selection RangesRanges can be combined/[A-Za-z0-9]/ - Matches an alphanumeric character/[A-Fa-f0-9]/ - Matches any hex characterCharacter Selection can be inversed/[^0-9]/ - Matches any non-digit character/[^ ]/ - Matches any non space character/[.!@#$%^*]/ - Matches some punctuation
  • 18. Special CharactersDot (.) matches any character/.//../ - Matches any two charactersTo match an actual dot character, you must escape/\./ - Matches a single dot characterUnless it’s a character selection/[.]/ - Matches a single dot character
  • 19. Character classes\d means [0-9]\D means non-digits - [^0-9]\w means word characters - [A-Za-z0-9_]\W means non word characters – [^A-Za-z0-9_]\s means a whitespace character [ \t\n\r]\S means non white space characters
  • 20. Repeating Character ClassesMatch two digits in a row/\d\d//[0-9][0-9]//\d{2}//[0-9]{2}/Match at least one digit (but as many as it can)/\d+/Match 0 to infinite digits/\d*/
  • 21. Repeating Character Classes cont.* means match 0 or more+ means match 1 or more{x} where x is a number means match exactly x of the preceding selection{x,} means match at least x{x,y} means match between x and y{,y} means match up to y
  • 22. More special characters? Means the preceding selection is optionalPutting it togetherTelephone Number/\(?(\d{3})\)?[\s-]?(\d{3})[\s-]?(\d{4})/Matches 720-675-7471 or (720)675-7471 or (720) 675-7471 or 7206757471 or 720 675 7471Find a misspelled word (and get great deals on EBay)/la[bp]topcomputer[s]?/
  • 23. Regex AnchorsAnchors allow you to specify a position, like before, after or in between characters/^ab/ matches abcdefg but not cabNotice that it’s the caret character… It means start of the string in this context, but means the opposite of a character class inside the square brackets/ab$/ matches cab but not abcdefg/^[a-z]+$/ will match a string that consists only of lowercase characters
  • 24. Word Boundaries\b means word boundariesBefore first character if first character is a word characterAfter last character if last character is a word characterBetween two characters if one is a word character and the other is not/\bfish\b/ matches fish, but not fisherman or catfish./fish\b/ matches fish and catfish
  • 25. Alternation/cow|boy/ - Matches cow, or boy or cowboy or coward, etc/\b(cow|boy)\b/ - Matches cow or boy but not cowboy or cowardThe above example also captures the matching word due to the parens. More on this later.
  • 26. Greedy vs LazyBy default, regular expressions are greedy… That is, they will match as much as they canGrab a starting html tag:/<.+>/ Matches in bold: <h1>Welcome to FRPUG</h1>Not what we wantMake it lazy: /<.+?>/Now it matches <h1>Welcome to FRPUG</h1>
  • 27. Another tag matching solution/<[^>]+>/Literally match a less than character followed by one or more non-greater than characters followed by a greater than characterThis way eliminates the need for the engine to backtrack (almost certainly faster than the last example).
  • 28. Capturing part of regex (backreference)/__(construct|destruct)/Backreference will contain either construct or destruct so you can use it later/([a-z]+)\1/Matches groups of repeated characters that repeat an even number of times.Matches aa but not a. Matches aaaaa/([a-z]{3})\1/Matches words like booboo or bambam
  • 29. Backreference Continued…Very useful when performing regex search and replacepreg_replace('/\(?(\d{3})\)?[\s-]?(\d{3})[\s-]?(\d{4})/', '(\1) \2-\3', $phone)The above example will take any phone number from the previous example and return it formatted in (xxx) xxx-xxxx format
  • 30. More backreferences…Replace duplicated words that that have been inadvertently left in
  • 31. Non-capturing groupsMatch an IPv4 address/((?:\d{1,3}\.){3}\d{1,3})/We’re matching 1 to 3 digits followed by a dot 3 times. We don’t care (right now) about the octets, we just want to repeat the match, so ?: says to not capture the group.
  • 32. Pattern Modifiers Modifiers go after the last delimiter (now you know why there are delimiters) and affect how the regex engine worksi – case insensitive matching (matches are case-sensitive by default)m – multiline matchings - dot matches all characters, including \nx – ignore all whitespace characters except if escaped or in a character class
  • 33. Pattern Modifiers Continued…D – Anchor for the end of the string only, otherwise $ matches \n charactersAllow username to be alphabetic only/^[A-Za-z]$/ - This will match dave\nextra stuffHowever, /^[A-Za-z]$/D will not matchU – Invert the meaning of the greediness. With this on by default matches are lazy and ? makes it greedy.There are lots of other modifiers and you can see them at http://us2.php.net/manual/en/reference.pcre.pattern.modifiers.php
  • 34. Named Capture GroupsRather than get back a numbered array of matches, get back an associative array.If you add a new capture group, you don’t have to renumber where you use the capture group
  • 35. Named Capture Groups cont…Use (?P<named_group>pattern)
  • 36. Named Capture Groups cont…Combined numbered and associative arrayCapture group 0 is the wholepattern that is matched.If our string to match against was abcde720-675 7471foobar, $matches[0] will contain720-675 7471
  • 37. Positive Look Ahead MatchesLook for a pattern follow by another pattern/p(?=h)/ - Match a “p” followed by an “h” but don’t include the “h”
  • 38. Negative Look AheadLook for a pattern which is not followed by some other pattern/p(?=!h)/ - pnot followed by h.
  • 39. Look AheadsPositive and negative look aheads do not capture anything. They just determine if the pattern match is possibleThey are zero-width/p[^h]/ is not the same as /p(?!h)//ph/ is not the same as /p(?=h)/
  • 40. Look behindsPositive look behind/(?<=oo)d/ - d which is preceded by ooMatches “food”, “mood”, match only contains the “d”Negative look behind/(?<!oo)d/ - d which is not preceded by ooMatches “dude”, “crude”, and “d”
  • 41. With great power…Test your regular expressions before they go to productionIt’s much easier to get them wrong than to get themright if you don’t test
  • 42. When to not use regexWhenever they aren’t needed.If you can use strstr or strpos or str_replace to do the job, do that. They are much faster, much simpler and easier to do correctly.However, if you cannot use those functions, regex may be your best bet.Don’t use regex when you really need a parser