Whoa!

/bin/[ as a binary looking for it's own "]" closing bracket!

What a nasty syntax hack!

I wonder what the motivation was for doing this rather than just implementing test expression support directly in the shell?

I just tried and bash also accepts some other odd filenames in place of "[", so you can do:

ln -s /bin/test "-"

ln -s /bin/test "$"

And use either of these in place of "[" (assuming they are on your path). Of course they still expect the closing "]" since that requirement comes from /bin/test.

It's an interesting way to extend bash in a confusing way! You could write a "$" utility that did something else entirely, perhaps looking for a "closing $" too, then write something like:

if $ args $;

then

fi