Having written the script, you can invoke it by sh
scriptname, [1] or alternatively bash
scriptname. (Not recommended is using sh <scriptname, since
this effectively disables reading from stdin within the
script.) Much more convenient is to make the script itself directly
executable with a chmod.
Either: chmod 555 scriptname (gives everyone read/execute
permission) [2]
Or chmod +rx scriptname (gives everyone read/execute
permission), chmod u+rx scriptname (gives only the script
owner read/execute permission).
Having made the script executable, you may now test it by
./scriptname. If it begins with a "sha-bang" line, invoking the
script calls the correct command interpreter to run it.
Why not simply invoke the script with scriptname? If the
directory you are in ($PWD) is where scriptname is
located, why doesn't this work? This fails because, for security
reasons, the current directory (./) is not by default included
in a user's $PATH. It is therefore necessary to explicitly
invoke the script in the current directory with a
./scriptname.
As a final step, after testing and debugging, you would likely want to
move it to /usr/local/bin (as root, of course), to make
the script available to yourself and all other users as a systemwide
executable. The script could then be invoked by simply typing
scriptname [ENTER] from the command-line.