1. REGULAR EXPRESSIONS CHAPTER 14

2. REGULAR EXPRESSIONS A coded pattern used to search for matching patterns in text strings Commonly used for data validation Patterns are strings inside single quotation marks and delimiters, usually /

3. REGULAR EXPRESSIONS Example pattern: $pattern = '/NC/'; The pattern is then sent with the string to a built-in PHP function.

4. REGULAR EXPRESSIONS preg_match(pattern, subject); returns 1 if the pattern is found, 0 if not, FALSE if there is an error in the pattern stops after the first match preg_match_all(); will find all matches

5. REGULAR EXPRESSIONS Create a regular expression: $pattern = '/Larry/'; Two strings to test: $author = 'Larry Ullman'; $editor = 'Rebecca Gulick'; Search for the pattern: $author_match = preg_match($pattern, $author); // $author_match is 1 $author_match = preg_match($pattern, $editor); // $author_match is 0

6. REGULAR EXPRESSIONS if ($author_match === false) { echo 'Error testing author name.'; } else if ($author_match === 0) { echo 'Author name does not contain Larry.'; } else { echo 'Author name contains Larry.'; }

7. DEFINING PATTERNS In addition to the literal characters being matched, meta-characters have other meanings: CharacterMeaning \Escape ^Beginning of a string $End of a string.Any single character except for newline |Or [ ]Beginning/ending of a class ( )Beginning/ending of a sub-pattern { }Beginning/ending of a quantifier

8. EXAMPLES Single character. $pattern = '/1.99/'; matches: 1.99, 1B99 or 1299 To match a period in a string, it must be escaped: $pattern = '/1\.99/'; matches: 1.99 only

9. EXAMPLES Specifying where characters are found: ^ at the beginning $ at the end $pattern = '/^a/'; matches any string beginning with the letter a $pattern = '/a$/'; matches any string ending with the letter a

10. EXAMPLES Pipe operator: | => or yes|no Grouping subpatterns: () (even|heavy) handed col(o|ou)r

11. CASE SENSITIVITY By default, a search is case sensitive. To perform a case-insensitive search, include a lowercase i after the closing / : $pattern = '/cat/i';

12. QUANTIFIERS CharacterMeaning ? 0 or 1 *0 or more +1 or more {x}Exactly x occurrences {x,y}Between x and y occurrences (inclusive) {x,}At least x occurrences Apply to the preceding character/group a{3} matches aaa a? matches 0 or 1 a's (ab)? matches 0 or 1 ab's

13. EXAMPLE Pattern for a five-digit number: $pattern = '/(0|1|2|3|4|5|6|7|8|9){5}/'; This will match 28403 but also will match 28403 contained within any other string. Use ^ and $ to match exactly: $pattern = '/^(0|1|2|3|4|5|6|7|8|9){5}$/';

14. CHARACTER CLASSES Square brackets define a set with an implied | or – for a range: [aeiou] matches a vowel (the | is implied) [a-z] matches any single lowercase letter [0-9] matches any single digit [A-Za-z] matches any character in the alphabet

15. CHARACTER CLASSES EXAMPLE A 3-letter, lowercase word: [a-z]{3} 5-digit zip code: ^[0-9]{5}$

16. CHARACTER CLASSES EXAMPLE $string = 'The product code is MBT-3461.'; preg_match('/MB[TF]/', $string); // Matches MBT and returns 1 preg_match('/[.]/', $string); // Matches. and returns 1 // Equivalent to preg_match('/\./', $string); preg_match('/[13579]/', $string); // Matches 3 and returns 1

17. METACHARACTERS characters which have special meanings in patterns such as / \. [ ] $ ^ ( ) – most metacharacters lose their special meanings inside a character class the exceptions: ^ (caret) negation: match any character except those in the class - (dash): represents a range of characters between the ones on either side to find a dash as part of a character class, the dash must be at the end.

18. METACHARACTERS Usage: $string = 'The product code is MBT-3461.'; preg_match('/MB[^FT]/', $string); // Matches nothing and returns 0 preg_match('/MBT[^^]/', $string); // Matches MBT- and returns 1 preg_match('/MBT-[1-5]/', $string); // Matches MBT-3 and returns 1 preg_match('/MBT[_*-]/', $string); // Matches MBT- and returns 1

19. CHARACTER CLASS SHORTCUTS ClassShortcutMeaning [0-9]\dAny digit [\f\r\t\n\v]\sAny white space [A-Za-z0-9]\wAny alphanumeric character [^0-9]\DNot a digit [^\f\r\t\n\v]\SNot white space [^A-Za-z0-9]\WNot an alphanumeric character

20. MORE DETAILED RESULTS Recall that the default for preg_match() is to stop and return 1 when the first occurrence of the pattern is found. To find out what, exactly, was found that matched the pattern include an optional 3 rd parameter: preg_match($pattern, $subject, $matches);

21. FINDING ALL MATCHES To find out how many matches were found, use preg_match_all() and include an optional 3 rd parameter: preg_match_all($pattern, $subject, $matches); This will return an integer or FALSE if there is an error in the pattern.

22. FINDING ALL MATCHES Additionally, preg_match_all($pattern, $subject, $matches); will put all of the found results into a multidimensional array assigned to $matches

23. USING MODIFIERS Pattern modifiers are parts of regular expressions, but these are placed after the ending delimiter. CharacterResult AAnchors the pattern to the beginning of the string IEnables case-insensitive mode MEnables multi-line matching SHas the period match every character including newline XIgnores most white space UPerforms as non-greedy match.

24. MATCHING AND REPLACING PATTERNS preg_replace($pattern, $replacement, $subject,$num) This function returns the altered (or unaltered if not found) $subject. The optional fourth parameter limits the number of replacements made.