Michael Kovalchik CS 265 Fall 2009 Parenthesis group parts of expressions together CS265 CS270 CS 265 270 Groups can be nested Perl Pearl P e a rl Parenthesis also serve to extract the matched strings abcde matched with abc de will match the string and store abc in the variable 1 and de in 2 Backreferences find earlier matches later in the string 1 is to match the group in 1 2 in 2 etc w w w s 1 matches when a three letter word is duplicated with a space between the copies The results of a regular expression search are stored in special variables tilde is set to the part of the string before a match is set to the part of the string that matched the expression single quote is set to the part of the string after a match Using and to a lesser extent slows regular expression processing Matches the preceding 1 or 0 times a match the character a 1 or 0 times a or Matches the preceding 1 or more times a match a atleast once a and aaaa Matches the preceding 0 or more times a match a any number of times a aaaa n m Matches atleast n but less than m times a 2 4 match a atleast 2 no more than 4 times aa and aaaa but not a or aaaaa n Match atleast n times a 3 match a atleast 3 times aaa and aaaaa but not a or aa n match exactly n times a 2 match a exactly 2 times aa only Perl Quantifiers will match the longest string possible the cat in the hat cat 1 the 2 cat 3 in the hat the cat in the hat at 1 the cat in the h 2 at 3 To have a quantifier match the smallest possible string append a to them Examples n m the cat in the hat at 1 the c 2 at 3 in the hat
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