Now whenever you type ls at the command line, the shell will actually execute ls -F . Note that the first argument to alias is the new alias. It doesn't have to be the same as the actual command it will represent. An environment variable is a variable whose contents are available to all processes spawned by the current shell. So if you set an environment variable and then run a program from the command line, that program will be able to access the contents of the environment variable you set.
Some programs depend on the contents of environment variables for proper operation.
By convention, all capital letters are used in environment variable names. This variable tells the man program where to look for manual pages. Shell Variables Shell variables are those which are not available to all spawned processes. An important shell variable is the path variable. It specifies where the shell should look for executable programs that you call.