my $conf_str = do { open my $fh, '<', 'work.conf' or die $!;
	local $/; <$fh> }; # slurp
( $conf_str =~ s/\bmy\s*\$folder\b/our \$folder/g )==1
	or die q{Failed to match "my $folder" exactly once};
our $folder;
my $config = eval $conf_str;