I want to check if the data that my user is giving me does not contain any Linux special character.

I would tend to turn the problem on its head and solve it the other way around. Rather than trying to exclude naughty characters, I think you would be more better serverd by only allowing permitted characters.

    if( $folder !~ /^[\w. -]+$/ ) {
        print "I don't like your $folder\n";
    }
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It is much easier and safer to relax a too-strict check, than it is to tighten up a too-lax requirement. There will always be someone smarter who finds (and exploits) the loop-hole before you do...