1. Regular Expressions Satyanarayana D < satyavvd@yahoo-inc.com>

5. History Stephen Kleene A mathematician discovered ‘ regular sets ’.

6. History Ken Thompson 1968 - Regular Expression Search Algorithm. Qed -> ed -> g/re/p

7. History Henry Spencer 1986 – Wrote a regex library in C

9. Grammar of Regex * RE = one or more non-empty ‘ branches ‘ separated by ‘|’ Branch = one or more ‘ pieces ’ Piece = atom followed by quantifier Quantifier = ‘*,+,?’ or ‘ bound ’ Bound = atom{n}, atom{n,}, atom {m, n} Atom = (RE) or () or ‘ ^,$,’ or followed by `^.[$()|*+?{ or any-char or ‘ bracket expression ’ Bracket Expression = is a list of characters enclosed in `[ ]'

10. Meta Chars? 2 + 4 Here ‘+’ has some special meaning In a normal Expression like :

11. Meta Chars Quote the next metacharacter ^ Match the beginning of the line . Match any character (except newline) = [^] $ Match the end of the line (or before newline at the end) | Alternation ( ) Grouping [ ] Character class { } Match m to n times * Match 0 or more times + Match 1 or more times ? Match 1 or 0 times

12. Non-printable Chars tab (HT, TAB) newline (LF, NL) return (CR) form feed (FF) alarm (bell) (BEL) escape (think troff) (ESC) 33 octal char (example: ESC) 1B hex char (example: ESC) {263a} long hex char (example: Unicode SMILEY) K control char (example: VT) {name} named Unicode character

14. POSIX Character Classes – [: … :] [^[:digit:] ]= = [^0-9]

15. Shorthand Chars word character [A-Za-z0-9_] decimal digit [0-9] whitespace [ ] not a word character [^A-Za-z0-9_] not a decimal digit [^0-9] not whitespace [^ ]

24. Non Greedy Quantifiers {,}? *? +? ?? To make non greedy quantifiers append ‘?’ <.+?> My first <strong> regex </strong> test. <strong> Use negated classes <[^>]+> My first <strong> regex </strong> test. <strong>

31. Float number = integerpart.factionalpart Matching a float number Basic Principle – Split your task into sub tasks

32. Integerpart = + -> will match one or more digits Matching a float number

33. Matching a float number Literal dot = Integerpart = + -> will match one or more digits

34. Matching a float number Literal dot = Integerpart = + -> will match one or more digits Fractional part= + -> will match one or more digits

35. Integerpart = + Matching a float number Literal dot = Fractional part = + Combine all of them = ++

36. Matching a float number /++/ -> Is generic. It won’t match -123.45 or +123.45

37. Matching a float number /++/ -> Is generic. It won’t match -123.45 or +123.45 /[+-]?++/ -> will match.

38. Matching a float number But It won’t match - 123.45 or + 123.45 /[+-]?++/ -> will match. /[+-]? *++/ -> will match. But It won’t match 123. or .45

39. Matching a float number /[+-]? *(?:++|+|+)/ -> will match. But It won’t match 123. or .45 /[+-]? * (?: ++ | + | + ) /

40. Matching a float number /[+-]? *(?:++|+|+)(?:[eE]+)?/ -> will match. But It won’t match 10e2 or 101E5 / [+-]? * (?: ++ | + | + ) (?: [eE]+ )? /

41. Matching a float number /^[+-]? *(?:++|+|+)(?:[eE][+-]?+)?$/ -> will match. But It won’t match 10e-2 / ^[+-]? * (?: ++ | + | + ) (?: [eE][+-]?+ )? $/x

42. Match a float number /^ [+-]?* # first, match an optional sign (?: # then match integers or f.p. mantissas: ++ # mantissa of the form a.b |+ # mantissa of the form a. |+ # mantissa of the form .b |+ # integer of the form a ) (?:[eE][+-]?+)? # finally, optionally match an exponent $/x;

46. Look Around Ahead Behind Positive Negative Positive Negative (?=...) (?!...) (?<=...) (?<!...) (?=...) Zero-width positive lookahead assertion (?!...) Zero-width negative lookahead assertion (?<=...) Zero-width positive lookbehind assertion (?<!...) Zero-width negative lookbehind assertion *Note : Assertions can be nested. Example : /(?<=, (?! (?<=,)(?=) ) )/

53. Inline modifiers & Comments Matching can be modified inline by placing modifiers. (?i) enables case-insensitive mode (?m) enables multiline matching for ^ and $ (?s) makes dot metacharacter match newline also (?x) ignores literal whitespace (?U) makes quantifiers ungreedy (lazy) by default $answers =~ / (?i) y (?-i) (?:es)?/ -> Will match ‘y’, ’Y’, ’yes’, ’Yes’ but not ‘YES’. Comments can be inserted inline using (?#) construct. /^ (?#begin) + (?#match integer part) (?#match dot) + (?#match fractional part) $/

54. Regex Testers Tools Editors Vim, TextMate, Edit Pad Pro, NoteTab, UltraEdit RegexBuddy Reggy – http:// reggyapp.com http://rubular.com (Ruby) RegexPal (JavaScript) - http://www.regexpal.com http://www.gskinner.com/RegExr/ http://www.spaweditor.com/scripts/regex/index.php http://regex.larsolavtorvik.com/ (PHP, JavaScript) http://www.nregex.com/ ( .NET ) http://www.myregexp.com/ ( Java ) http://osteele.com/tools/reanimator ( NFA Graphic repr. ) Expresso - http://www.ultrapico.com/Expresso.htm ( .NET ) Regulator - http://sourceforge.net/projects/regulator ( .NET ) RegexRenamer - http://regexrenamer.sourceforge.net/ ( .NET ) PowerGREP http://www.powergrep.com/ Windows Grep - http://www.wingrep.com/

55. Regex Resources $perldoc perlre perlretut perlreref $man re_format “ Mastering Regular Expressions” by Jeffrey Friedl http://oreilly.com/catalog/9780596528126/ “ Regular Expressions Cookbook” by Jan Goyvaerts & Steven Levithan http://oreilly.com/catalog/9780596520694

56. Questions? * { } ^ ] + $ [ ( ? . ) - : #

57. Thank Y!ou * { } ^ ] + $ [ ( ? . ) - : #

64. Unicode Properties

66. Commify a number $no=123456789; substr($no,0,length($no)-1)=~s/(?=(?<=)(?:)+$)/,/g; print $no’ Produce 12,34,56,789

67. Find Incremental numbers ? $str=&quot;abc 123 hai cde 34567 efg 1245 a132 123456789 10adf&quot;; print &quot;$1&quot; while($str=~/ ( () (?{$x=$2}) ( (??{++$x%10}) )* ) /gx);’ Non Capture group in a capture group won’t work : perl -e '$x=&quot;cat cat cat&quot;;$x=~/(cat(?:+))/;print &quot;:$1:&quot;;’