in reply to Can't exec "command": No such file or directory error

I don't know much about zsh, but my best guess is that this might be The problem of "the" default shell. You might try system('/bin/zsh','-c','command task list');, but be aware of the security implications of doing this with with anything other than a fixed string.

Update: What is task? Because if it's a binary then my advice here is wrong - see my reply here.