[comex]

Because shell is so deficient that even for "simple" things it is really easy to screw up - when whitespace or special characters in filenames cause some case you overlooked to screw up due to terrible quoting rules, when missing arguments cause [1], when you accidentally put bashisms in scripts labeled /bin/sh, when you suddenly have to do some basic text parsing (e.g. extracting capture groups from a regex) and have to either switch to perl or use some ugly bash extension that's incompatible between the version of bash OS X uses and the newer ones.

So you might want to use a different language - even for purely/mostly personal use, in which case Haskell would be fine.

[1] https://github.com/ValveSoftware/steam-for-linux/issues/3671

[regularfry]

That's before you've even addressed the stultifying features of shell as a language: booleans and tests are odd, arrays are odder, they have things called "functions" which don't have return values, the list goes on. Basically if you're writing shell, you probably also have at least Perl available, and probably Python...