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106 lines
2.6 KiB
Perl
106 lines
2.6 KiB
Perl
#Greedy Matches!
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$p="pattern";
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#A greedy match matches the entire pattern
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$p =~ /(.*)/;
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print "1==>$1<==\n";
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#Greedy and non-greedy quantifiers!
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#!usr/bin/perl
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use strict;
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use warnings;
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my $string1 = "there here There here there Here";
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my $string2 = $string1;
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print "$string1\n";
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$string1 =~ s/N.*here\.//;
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print "$string1\n";
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print "$string2\n";
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$string2 =~ s/N.*?here\.//;
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print "$string2\n\n";
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#Greedy searches!
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greedy means that each pattern will try to match as much as it can.
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The pattern /a.*a/ matches as many characters as possible between the first a and the last a.
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If your text string is ababacdea, /a.*a/ will match the whole string.
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You can control the greediness using a question mark.
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The question mark matches a minimum number of times.
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The following table shows how to minimize the greediness.
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Syntax Means
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*? Match zero or more times, minimal number of times
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+? Match one or more times, minimal number of times
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?? Match zero or one time, minimal number of times
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{num}? Match exactly num times, minimal number of times
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{num,}? Match at least num times, minimal number of times
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{num,max}? Match at least num but not more than max times, minimal number of times
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#The Greedy Metacharacters!
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Metacharacter What It Matches
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x? Matches 0 or 1 occurrences of x
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(xyz)? Matches 0 or 1 occurrences of pattern xyz
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x* Matches 0 or more occurrences of x
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(xyz)* Matches 0 or more occurrences of pattern xyz
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x+ Matches 1 or more occurrences of x
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(xyz)+ Matches 1 or more occurrences of pattern xyz
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x{m,n} Matches at least m occurrences of x and no more than n occurrences of x
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#The greedy quantifier!
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$string="ABCdefghiCxyzwerC YOU!";
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$string=~s/.*C/HEY/;
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print "$string", "\n";
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#Turning Off Greediness!
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Metacharacter What It Matches
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x?? Matches 0 or 1 occurrences of x
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(xyz)?? Matches 0 or 1 occurrences of pattern xyz
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x*? Matches 0 or more occurrences of x
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(xyz)*? Matches 0 or more occurrences of pattern xyz
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x+? Matches 1 or more occurrences of x
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(xyz)+? Matches 1 or more occurrences of pattern xyz
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x{m,n}? Matches at least m occurrences of x and no more than n occurrences of x
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x{m}? Matches at least m occurrences of x
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x{m,}? Matches at least m times
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