[TW-1696] Certain symbols in a filter cause errors

_Alan Young on 2015-09-16T14:07:07Z says:_

If any of '!', '%', '^', '*', '-', '/', '[' or '{' are included in a filter string task errors with one of the following, depending on the symbol.

Cannot divide real numbers by strings
Cannot exponentiate strings
Cannot modulo string values
Cannot multiply strings by strings
Cannot subtract strings
Unmatched \{
Unmatched [ or [^

I've attached the bash script and output files.