The user input is going to be passed to the shell, I take it? It's certainly not safe to just escape semicolons and backticks. An ampersand has about the same effect as a semicolon, for example, and a pipe character will also cause another program to be launched. So is it safe to escape semicolons, backticks, ampersands, and pipes? Maybe; to know for sure you'd have to become an expert on a wide variety of shells and how they're launched from within perl, make sure none of the characters that effect the shell on any platform your script might run under are escaped, and bet the security of your application on your expertise being flawless. In Perl's spirit of laziness, that's probably not the best possible approach. :-)

Depending on what you want to do, there could be other options. If you use the multi-argument form of system or exec, shell characters aren't processed, so that's pretty safe. quotemeta is a fairly safe approach, too.

Of course, if you're not passing this data as arguments to a shell command, the rules are entirely different; whether they're easier or harder to work with depends on what you're doing with the data.