Then you'd have 
$str =~ s/(\d*)%var%(.*)/$1REPLACED$2/;

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Although, unless you're going to use $1 and/or $2 later, there's no reason to have them at all. 
$str =~ s/%var%/REPLACED/;

[download]

In reply to Re^3: Regex triggering uninitialised values by Eimi Metamorphoumai
in thread Regex triggering uninitialised values by kiat

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