[dozzie]

It's much simpler than you would want to paint it.

  [dozzie@alojzy dozzie]$ `echo for` i in 1 2 3 4; do echo $i; done
  zsh: parse error near `do'
  [dozzie@alojzy dozzie]$ bash -c '`echo for` i in 1 2 3 4; do echo $i; done'
  bash: -c: line 0: syntax error near unexpected token `do'
  bash: -c: line 0: ``echo for` i in 1 2 3 4; do echo $i; done'

I think parser generator will be sufficient, no need to resort to I-can't-write-grammars recursive descent.

Unless you were talking about csh syntax; that one I never learned, so I don't know if it is context-free.