Presentation at LDC09: Introduction To Regex in Lasso 8.5

1. Beginner Track: Introduction to Regular Expressions (aka “regex”) Bil Corry lasso.pro

2. What is regex? “ Regular expressions provide a concise and flexible means for identifying strings of text of interest, such as particular characters, words, or patterns of characters.” ( Wikipedia: http://en.wikipedia.org/wiki/Regex) In plain English: Regex is a text-searching “language.”

4. Some text to search against

5. A regular expression that defines what to search for (e.g. “” to find a digit)

7. [string_replaceregexp]

8. [regexp]

9. [compare_regexp]

10. [compare_notregexp]

11. [match_regexp]

12. [match_notregexp]

14. There may be performance and memory challenges using regex against a sizably large [string]

16. Dot

17. White Space

18. Character Classes

20. Alternation

21. Quantifiers

22. Grouping

23. Literals All characters search for their literal selves except for the following: “ [$.|?*+()” – they require being escaped when searched for as a literal. Example: [string_findregexp('LDC is fun!',-find='fun')] LP8: array: (fun) L9: array(fun)

24. Literals (cont) By default, regex is case-sensitive. Use the (?i) switch to make it case-insensitive. Examples: [string_findregexp('ABC abc',-find='abc')] LP8: array: (abc) L9: array(abc) [string_findregexp('ABC abc',-find='(?i)abc')] LP8: array: (ABC), (abc) L9: array(ABC, abc)

25. Escaping Characters In regular expressions, depending on the context, various characters have special meaning. In order to specify the literal character, you must escape it with a backslash (“). And because the backslash has special meaning in Lasso, it means you must double the backslashes in Lasso (“”).

26. Escaping Characters (cont) Example: [string_findregexp('[date] returns the date', -find='[date]')] LP8: array: ([date]) L9: array([date]) [string_findregexp('[date] returns the date', -find='[date]')] LP8: array:(d),(a),(t),(e),(e),(t),(t),(e),(d),(a),(t),(e) L9: array(d, a, t, e, e, t, t, e, d, a, t, e)

27. Dot A dot (aka period symbol “.”) will match any single character except line returns. Use the switch “(?s)” to turn on matching line returns too. Example: [string_findregexp('LDC is fun! Turn on a fan.', -find='f.n')] LP8: array: (fun), (fan) L9: array(fun, fan)

28. Dot (cont) [string_findregexp('123',-find='.')] LP8: array: (1), (2), (3) L9: array(1, 2, 3) [string_findregexp('123',-find='(?s).')] LP8: array: (1), ( ), (2), ( ), (3) L9: array(1, , 2, , 3)

29. White Space To find white space, use the Lasso equivalents: Return = Newline = Tab = Example: [string_findregexp('123',-find='')] LP8: array: ( ), ( ) L9: array( , )

30. Character Classes Used to match against a set of characters contained within square brackets “[ … ]”. Order of characters within the class does not matter (i.e. [abc] == [cba]). Reserved characters are “ ^-]. Example: [string_findregexp('New Years Eve is 2009-12-31', -find='[123ae]')] LP8:array: (e), (e), (a), (e), (2), (1), (2), (3), (1) L9: array(e, e, a, e, 2, 1, 2, 3, 1)

31. Character Classes (cont) Hyphen denotes a range (e.g. “[0-9]” means 0,1,2,..,9 and [a-z] means a,b,c,...,z). Example: [string_findregexp('abcdef',-find='[b-d]')] LP8: array: (b), (c), (d) L9: array(b, c, d)

32. Character Classes (cont) A caret after the opening square bracket denotes characters to omit instead of find. Example: [string_findregexp('abcdef',-find='[^b-d]')] LP8: array: (a), (e), (f) L9: array(a, e, f)

33. Shorthand Character Classes d = [0-9] D = [^0-9] w ≈ [a-zA-Z0-9_] W ≈ [^a-zA-Z0-9_] s ≈ [] S ≈ [^] Example: [string_findregexp('1a2b3c',-find='d')] LP8: array: (1), (2), (3) L9: array(1, 2, 3) [string_findregexp('1a2b3c',-find='D')] LP8: array: (a), (b), (c) L9: array(a, b, c)

34. Shorthand Character Classes (cont) Example: [string_findregexp('1a2b3c',-find='w')] LP8: array: (1), (a), (2), (b), (3), (c) L9: array(1, a, 2, b, 3, c) [string_findregexp('123',-find='s')] LP8: array: ( ), ( ) L9: array( , )

35. Positional Matching “^” matches beginning of text, “$” matches end of text, and (?m) switch makes ^ and $ match beginning and ending of each line. Example: [string_findregexp('123',-find='^d')] LP8: array: (1) L9: array(1) [string_findregexp('123',-find='(?m)^d')] LP8: array: (1), (2), (3) L9: array(1, 2, 3)

36. Positional Matching (cont) “b” matches a word boundary (the position between a word character and a non-word character or start/end of line). Example: [string_findregexp('cape and ape',-find='bape')] LP8: array: (ape) L9: array(ape) [string_findregexp('cape and ape',-find='ape')] LP8: array: (ape), (ape) L9: array(ape, ape)

37. Alternation Vertical bar (“|”) is an OR operand for regex. Example: [string_findregexp('cat and rat',-find='cat|rat')] LP8: array: (cat), (rat) L9: array(cat, rat)

38. Quantifiers Specifies the number to find: * = 0 or more + = 1 or more ? = 0 or 1 {n} = n times {n,m} = min n, max m times {n, } = min n, no max Example: [string_findregexp('123aaabbb', -find='0*1+2?3{1}a{1,2}ab{2,}')] LP8: array: (123aaabbb) L9: array(123aaabbb)

39. Grouping Round brackets “( )” group the regex together, allowing quantifiers to be used on the group or to perform AND/OR with regex. They also create backreferences, which we won't cover in this session, but know that Lasso returns the group match in addition to the overall match. Example: [string_findregexp('cat and rat',-find='(c|r)at')] LP8: array: (cat), (c), (rat), (r) L9: array(cat, c, rat, r)

40. Grouping (cont) There is an option for non-capturing groups: “(?: … regex here...)” Example: [string_findregexp('cat and rat',-find='(?:c|r)at')] LP8: array: (cat), (rat) L9: array(cat, rat)

42. When using regular expressions obtained from outside sources, you'll need to double-up the backslashes (“) for Lasso (e.g. “+” becomes “d+”).

43. User-input used as part of a regular expression must be encoded (http://tagswap.net/lp_regexp_encode)

45. Often, there are several ways to match. If one approach doesn't work, try another.

46. Great reference and tutorial site: www.regular-expressions.info

47. Examples Extract names from comma-delimited list: [string_findregexp('Abe Smith, Bob Jones, Cindy Hart, Darla King',-find='w+s+w+')] LP8: array: (Abe Smith), (Bob Jones), (Cindy Hart), (Darla King) L9: array(Abe Smith, Bob Jones, Cindy Hart, Darla King)

48. Examples (cont) Extract phone numbers into a packed format: [string_findregexp('(213) 555-1212',-find='d') ->join('')] [string_findregexp('213-555-1212',-find='d') ->join('')] [string_findregexp('213 555 1212',-find='d') ->join('')] LP8: 2135551212 2135551212 2135551212 L9: 2135551212 2135551212 2135551212

49. Examples (cont) Extract data from HTML: [string_findregexp('<input type=&quot;hidden&quot; name=&quot;secret&quot; value=&quot;123&quot;>',-find='name=&quot;secret&quot; value=&quot;[^&quot;]+')] LP8: array: (name=&quot;secret&quot; value=&quot;123) L9: array(name=&quot;secret&quot; value=&quot;123) [string_findregexp('<input type=&quot;hidden&quot; name=&quot;secret&quot; value=&quot;123&quot;>',-find='name=&quot;secret&quot; value=&quot;([^&quot;]+)')] LP8: array: (name=&quot;secret&quot; value=&quot;123), (123) L9: array(name=&quot;secret&quot; value=&quot;123, 123)

50. Examples (cont) Extract data from HTML: [string_findregexp('<input type=&quot;hidden&quot; name=&quot;secret&quot; value=&quot;123&quot;>',-find='(?:name=&quot;secret&quot; value=&quot;)[^&quot;]+')] LP8: array: (name=&quot;secret&quot; value=&quot;123) L9: array(name=&quot;secret&quot; value=&quot;123) [string_findregexp('<input type=&quot;hidden&quot; name=&quot;secret&quot; value=&quot;123&quot;>',-find='(?<=name=&quot;secret&quot; value=&quot;)[^&quot;]+')] LP8: array: (123) L9: array(123)

51. Thank You! Questions?