my $outputfile = "${str}output_$key";
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BTW, if you want to keep the name of the directory in a variable, don't call it $str, call it $dir. And use it everywhere. So, you can replace

mkdir("dict");
my $str="dict/";
opendir(DIR,$str);
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with

mkdir my $directory_name = 'dict' or die $!;
opendir my $dir_handle, $directory_name or die $!;

...

my $outputfile = "$directory_name/output_$key";
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($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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