And in order to also include the tilde character which was omitted for some reason:

perl -pe 'tr{\x20-\x7e}{\x50-\x7e\x4f\x20-\x4e}' clear.txt > cipher.txt

The expression is a bit more difficult to read/parse/write that way (essentially because an uneven number of characters in the initial alphabet needs a pivot element in the middle that is not rotated at all), but provides a bit more coverage.