One group where I worked did such a script, to push a bunch of 'csh' scripts into the new Millennium. We wrote a simplistic mechanical translator. The scripts were a bunch of cut-and-paste monstrosities, and the results were just as cruddy. Don't expect human-readable, maintainable results.

One word of advice, anything that requires punting on the translator side should at least KNOW that it requires punting. Output a comment with '#REVIEW:' next to any surely-incomplete translated statements, for example. Then you have a little bit less work to do in hunting down the worst problems with the translated scripts.

The rest of the problems will lurk in obscurity forever.