Here's my go at it, with a nod to smokemachine:

print "debug mode\n" if shift;
read INFILE, my $infile, -s '/path/to/infile'; #<- not specified in OP
close(INFILE);
my ($old_version) = $infile =~ /^.*?ver = '(.*?)'/;
(my $projlabl = $projectPath) =~ s/\.pro/labeler/;
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