I am trying to pass those expressions from the command line. It works fine the way you have your code written, but try this:

my ($find, $rep) = @ARGV;

$s = "The quick brown fox jumps over the lazy dog";;

$s =~ s[$find][$rep]eg;;


./arg.pl '\x20' '\x30'

#prints:

The\x30quick\x30brown\x30fox\x30jumps\x30over\x30the\x30lazy\x30dog
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