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Ruby, 81 78 68 66 62 57

(?!..?~).map{|a|$><<a if/[()ifmap{}|?!.~\/\\\[\]$><]/!~a} 

Simply checks itself. Duplicate characters manually removed.

Thanks to minitech for saving 5 characters!

Ruby, 81 78 68 66 62 57

(?!..?~).map{|a|$><<a if/[()ifmap{}|?!.~\/\\\[\]$><]/!~a} 

Simply checks itself. Duplicate characters manually removed.

Thanks to Josh for saving 4 characters, and minitech for saving 5 characters!

Ruby, 81 78 68 66 62

for x in ?!..?~ $><<x if/[^for xin?!.~\/\\\[^\]=$><ed]/=~x end 

Simply checks itself. Duplicate characters manually removed.

Ruby, 81 78 68 66 62 57

(?!..?~).map{|a|$><<a if/[()ifmap{}|?!.~\/\\\[\]$><]/!~a} 

Simply checks itself. Duplicate characters manually removed.

Thanks to minitech for saving 5 characters!

Ruby, 81 78 68 66

for x in ?!..?~ if/[^for xin?!.~\/\\\[^\]=$><ed]/=~x $><<x end end 

Simply checks itself. Duplicate characters manually removed.

Ruby, 81 78 68 66 62

for x in ?!..?~ $><<x if/[^for xin?!.~\/\\\[^\]=$><ed]/=~x end 

Simply checks itself. Duplicate characters manually removed.