ls lists contents of the current working directory. PyMOL comes with a few commands that allows the user to traverse a directory structure and list files. This is a powerful tool if you have many directories full of files --- you don't have to quit PyMOL, you can just cd to the directory and ls to find the contents.
ls [pattern] dir [pattern]
# list all files in the current directory ls # list all files ending in, pml, in the current directory. ls *.pml