My rule (and the code review policy I impose) emphasizes complexity instead - a 50 line shell script is great if it doesn't use if or case. (It's not so much of a strict rule as "once you're nesting conditionals, or using any shell construct that really needs a comment to explain the shell and not your code, you should probably already have switched to python." This is in parallel with "error handling in this case is critical, do you really think your bash is accurate enough?")

I wasn't the strictest reviewer (most feared, sure, but not strictest) at least partly because my personal line for "oh that bit of shell is obvious" is way too high.