How to obtain the absolute path of a file via Shell (BASH/ZSH/SH)?

Question: is there a simple sh/bash/zsh/fish/... command to print the absolute path of whichever file I feed it? Usage case: I'm in directory /a/b and I'd like to print the full path to file c on the command-line so that I can easily paste it into another program: /a/b/c. Simple, yet a little program to do this could probably save me 5 or so seconds when it comes to handling long paths, which in t