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Posted by PerlFAQ Server on May 3, 2008, 3:03 am
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This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .
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4.21: How do I remove consecutive pairs of characters?
(contributed by brian d foy)
You can use the substitution operator to find pairs of characters (or
runs of characters) and replace them with a single instance. In this
substitution, we find a character in "(.)". The memory parentheses store
the matched character in the back-reference "" and we use that to
require that the same thing immediately follow it. We replace that part
of the string with the character in $1.
s/(.)/$1/g;
We can also use the transliteration operator, "tr///". In this example,
the search list side of our "tr///" contains nothing, but the "c" option
complements that so it contains everything. The replacement list also
contains nothing, so the transliteration is almost a no-op since it
won't do any replacements (or more exactly, replace the character with
itself). However, the "s" option squashes duplicated and consecutive
characters in the string so a character does not show up next to itself
my $str = 'Haarlem'; # in the Netherlands
$str =~ tr///cs; # Now Harlem, like in New York
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