Read perlref. You need to do something like &{$filename}. BTW, your example code won't work anyway.

sub mysub($) {
  my $str = shift;
  #code
}

$filename = 'somefile.ext';
open IN, $filename;
$subref = <$filename>;  # maybe it's 'mysub'?
chomp $subref;
no strict 'refs';
no strict 'subs';
&{$subref}( 'text' );
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Hope this helps,

Jeroen
"We are not alone"(FZ)