The test builtin command is used to evaluate conditional expressions; it tests whether two strings are equal, whether a file exists, whether a string is empty, and other functions. The complete list of tests is available with help test.
For example, to test whether a file exists, you might use the following:
$ test -e /etc/passwd && echo 'Password file exists!' Password file exists!
There is an alternative way to write this command, called [. No, that's not a typo; [ is the name of the command! We can see this with type; there's even a program on our filesystem by the same name:
bash$ type -a [ [ is a shell builtin [ is /usr/bin/[
The primary difference between test and [ is that [ requires its last argument to ...
