Re: Replace the last letter

#!/usr/bin/perl

use strict;
use warnings;

my $tofind="s";
my $replacement="X";
my $variable="snaskes";

print "Before: $variable\n";

$variable =~ s/$tofind[^$tofind]*$/$replacement/;

# OR
# $variable =~ s/$tofind(?![$tofind])$/$replacement/;

print "After: $variable\n";
[download]

Comment on Re: Replace the last letter Download Code

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Re^2: Replace the last letter by hv (Prior) on Oct 08, 2004 at 15:10 UTC
The main version does the right thing, but the alternative doesn't - negative lookahead will look for something immediately following, so: `$variable =~ s/$tofind(?![$tofind])$/$replacement/;` [download] means "find the letter, not followed by the letter again, but followed by the end anchor". I think you want instead: `$variable =~ s/$tofind(?!.*$tofind)/$replacement/;` [download] ie "find the letter, not followed by (zero or more characters and) the letter again". Also, the `[$tofind]` character class is the same as `$tofind` itself when it refers to a single letter, but doesn't do the right thing if `$tofind` is something more complex. Hugo	[reply] [d/l] [select]

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Re^2: Replace the last letter
by hv (Prior) on Oct 08, 2004 at 15:10 UTC

The main version does the right thing, but the alternative doesn't - negative lookahead will look for something immediately following, so:

  $variable =~ s/$tofind(?![$tofind])$/$replacement/;
[download]

  $variable =~ s/$tofind(?!.*$tofind)/$replacement/;
[download]

Also, the [$tofind] character class is the same as $tofind itself when it refers to a single letter, but doesn't do the right thing if $tofind is something more complex.

Hugo

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