ruby 的回溯 正則表達(dá)式

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ruby 的回溯 正則表達(dá)式

matchesrubyregular expression
Ruby代碼

1. ^ - Matches beginning of line   
   
2. $ - Matches end of line   
   
3. \A - Matches beginning of string.   
   
4. \Z - Matches end of string. If string ends with a newline, it matches just before newline   
   
5. \z - Matches end of string   
   
6. \G - Matches point where last match finished   
   
7. \b - Matches word boundaries when outside brackets; backspace (0x08) when inside brackets   
   
8. \B - Matches non-word boundaries   
   
9. (?=pat) - Positive lookahead assertion: ensures that the following characters match pat, but doesn't include those characters in the matched text   
   
10. (?!pat) - Negative lookahead assertion: ensures that the following characters do not match pat, but doesn't include those characters in the matched text   
    
11. (?<=pat) - Positive lookbehind assertion: ensures that the preceding characters match pat, but doesn't include those characters in the matched text   
    
12. (?<!pat) - Negative lookbehind assertion: ensures that the preceding characters do not match pat, but doesn't include those characters in the matched text   
    
13. # If a pattern isn't anchored it can begin at any point in the string   
    
14.   
    
15. /real/.match("surrealist") #=> #<MatchData "real">   
    
16. # Anchoring the pattern to the beginning of the string forces the   
    
17. # match to start there. 'real' doesn't occur at the beginning of the   
    
18. # string, so now the match fails   
    
19. /\Areal/.match("surrealist") #=> nil   
    
20. # The match below fails because although 'Demand' contains 'and', the   
    
21. pattern does not occur at a word boundary.   
    
22. /\band/.match("Demand")   
    
23. # Whereas in the following example 'and' has been anchored to a   
    
24. # non-word boundary so instead of matching the first 'and' it matches   
    
25. # from the fourth letter of 'demand' instead   
    
26. /\Band.+/.match("Supply and demand curve") #=> #<MatchData "and curve">   
    
27. # The pattern below uses positive lookahead and positive lookbehind to   
    
28. # match text appearing in <b></b> tags without including the tags in the   
    
29. # match   
    
30. /(?<=<b>)\w+(?=<\/b>)/.match("Fortune favours the <b>bold</b>")   
    
31.     #=> #<MatchData "bold">  
    
32. 
    
33. 
    
34. ^ - Matches beginning of line
    
35. $ - Matches end of line
    
36. \A - Matches beginning of string.
    
37. \Z - Matches end of string. If string ends with a newline, it matches just before newline
    
38. \z - Matches end of string
    
39. \G - Matches point where last match finished
    
40. \b - Matches word boundaries when outside brackets; backspace (0x08) when inside brackets
    
41. \B - Matches non-word boundaries
    
42. (?=pat) - Positive lookahead assertion: ensures that the following characters match pat, but doesn't include those characters in the matched text
    
43. (?!pat) - Negative lookahead assertion: ensures that the following characters do not match pat, but doesn't include those characters in the matched text
    
44. (?<=pat) - Positive lookbehind assertion: ensures that the preceding characters match pat, but doesn't include those characters in the matched text
    
45. (?<!pat) - Negative lookbehind assertion: ensures that the preceding characters do not match pat, but doesn't include those characters in the matched text
    
46. # If a pattern isn't anchored it can begin at any point in the string
    
47. 
    
48. /real/.match("surrealist") #=> #<MatchData "real">
    
49. # Anchoring the pattern to the beginning of the string forces the
    
50. # match to start there. 'real' doesn't occur at the beginning of the
    
51. # string, so now the match fails
    
52. /\Areal/.match("surrealist") #=> nil
    
53. # The match below fails because although 'Demand' contains 'and', the
    
54. pattern does not occur at a word boundary.
    
55. /\band/.match("Demand")
    
56. # Whereas in the following example 'and' has been anchored to a
    
57. # non-word boundary so instead of matching the first 'and' it matches
    
58. # from the fourth letter of 'demand' instead
    
59. /\Band.+/.match("Supply and demand curve") #=> #<MatchData "and curve">
    
60. # The pattern below uses positive lookahead and positive lookbehind to
    
61. # match text appearing in <b></b> tags without including the tags in the
    
62. # match
    
63. /(?<=<b>)\w+(?=<\/b>)/.match("Fortune favours the <b>bold</b>")
    
64.     #=> #<MatchData "bold">

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