If you always want the last letter, you could match: 

$string =~ s/.$/X/;
## or
$letter = 'X';
$string =~ s/.$/$letter/;

[download]
As opposed to the substr use.

radiantmatrix
require General::Disclaimer;

In reply to Re^3: Replace the last letter by radiantmatrix
in thread Replace the last letter by Anonymous Monk

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