You need String::Interpolate (or something similar) and the /e modifier: 
use String::Interpolate qw(safe_interpolate);

...

$line =~ s/$key/safe_interpolate($fsr_hash{$key})/e;

[download]

(Untested). If you are sure that there are no "evil" components in the replace string you can use eval to do the work of String::Interpolate.

In reply to Re: backreferencing fails in a search and replace with a hash by moritz
in thread backreferencing fails in a search and replace with a hash by tonyz

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