A more interesting command is /bin/[.

Yep, it's the same as /bin/test, but basically requires the last argument to be a ]. Typically /bin/test and bin/[ are hard links, that is, they are physically the same file and share the same inode(s).

You know, so you can type

  if [ $foo = $bar ]; then
    yes
  else
    exit
  fi

This actually runs the command /bin/[, except most of the time it doesn't, because it's built-in to the shell.

As as side-note, an article like this should at least mention which OS and shell the author is using.