You didn't read the conditional expressions in man bash *and*
you didn't read
my previous post. This is boring..
not 'if [ f foo ]', but 'if [ -f foo ]', as in my example.
Why -f this time, and -e on the previous? See the 'conditional expressions', in bash manual page.
What does the last sentence mean?
Type: 'man bash' and look for the section that has a title 'CONDITIONAL EXPRESSIONS'.
Or read an online version
.. or maybe you did read those. I'm just too tired right now and go back to sleep...