Your problem is only partly that the string contains special Perl characters.

1. When you assign to $INVALID_STRING, make sure you protect yourself from interpolation. '"!"' etc. just don't end up in your variable. In this case, you can use the generic single quote op q:

$INVALID_STRING = q{!"$\%&'()*/@`~}; Here { ... } act as the delimiters, but many other options are available. See perlop for details.

2. Your main problem is that the *shell* is having a hard time dealing with the string, not perl. This is your main problem because it's harder to solve :-)

I'm afraid that this will depend a bit on which shell your system uses; experiment a bit with escaping ! and ' and putting everything in single quotes.

In reply to Re: Error using back tick operators if it has special perl chars in it by gaal
in thread Error using back tick operators if it has special perl chars in it by Anonymous Monk

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