unix - Purpose of square brackets in shell scripts

Question

I came across this line in one of the shell scripts:

[-f $host_something ] && .$host_something

What are the square brackets with the -f switch supposed to do, and what is the point of ANDing it with the same environment variable?

Answer 1

The [ is actually an actual binary. It's an alias for the test(1) command. It will ignore it's last argument which should be ]. Run man test for further information. It's not really shell syntax.