What's not so funny is that /bin/[ has no way of enforcing this syntax rule, or any other. Just like sed can't enforce any syntax rules on its regular expressio

What's not so funny is that /bin/[ has no way of enforcing this syntax rule, or any other. Just like sed can't enforce any syntax rules on its regular expressions. This is why the shell is still a crock of shit for scripting even with "set -e" on. The invoked binary has no way of aborting script execution. All it can do is barf out on stderr and return an error code, which the shell interprets as false and `if [ "x" = "x"` (without ]) goes into the else branch.