I am a windows user but I use bash a lot. Some of the internships that I am applying to require "demonstrated experience with Unix and/or Linux operating systems." I was wondering if Bash counts on cplusplus
Bash itself is just a command shell. A shell in this case is (loosely) just an interface to abstract and make working with the OS. A command shell is (somewhat loosely) one that allows you to interactively and/or batch execute commands. Just knowing the Bash language alone isn't really the same thing as knowing a Linux or Unix. However, it certainly helps to navigate one.
Generally, the best way to get comfortable with a flavor is to just use it. There's a lot of common software for both Linux or Unix (Sshd, Bash, and Apache Httpd to name a few), but there is also a lot of software that isn't (ip for Linux, SELinux for Redhat/Centos, or apt for Debian/Ubuntu), or may even just be configured to work differently. Understanding how this software works, and their quirks, can be difficult just by reading (although reading documentation and blog posts and such certainly doesn't hurt).
as an intern the experience may not be expected to be very much.
as in, can you make a folder, compress a file, compile a program, change your password, connect to another box, etc. the kinds of things you do at school, if you use unix there.
My last job wanted unix skills and all you had to know how to do was putty into a box to change your password and winscp into the box to move a file down or up. Anything else was a bonus. I think I wrote maybe 3 shell scripts, 2 of them < 10 lines, the third more complex because the guy who wanted wanted 500 logs entries to be written and a bunch of other extra junk that had nothing to do with the task at hand. Oh, and I compiled 2 or 3 programs into a library that served as plugins to a tool we used -- the tool had an interface that could call the library code directly and it was (100+ times) faster than doing the work in the tool itself.
if you want to play, cygwin lets you do most of the console stuff locally on windows. I keep it around so my windows box can do simple sed/grep/g++/ stuffs that windows does not generally have. Its 'not exactly right' in some places but its 'close enough'.
I encourage you to apply. Worst thing that can happen is they turn you down.... but they may not, and when your summer is over, you will have the experience you didn't have going in for sure :) If they turn you down, ask what they wanted, they will likely tell you.