1.12 What Makes a Shell Script?

A shell script is just an ASCII file (52.9 ) containing a saved sequence of commands.

If you were to store a list of commands in a file for one-time use, you could execute it by typing:

% sh mycommands

where mycommands is the name of the file containing the list of commands. This would tell the shell to treat the file as a list of commands to be executed.

But there's a better way to tell the shell to execute the contents of a file, and that is to make the file executable with the chmod (22.7 ) command:

% chmod +x mycommands

Then, all you have to do to execute the script is type its name. (To make it even easier to use, you should store it in a personal bin directory and add the bin to your search path .) (8.7 )

Of course, in either case, all of the lines in the file need to be meaningful to the shell! If you accidentally made a letter to your mother executable, and tried to run it as a shell script, you'd get error messages like this, containing the first word of each line in the letter:

letter: Dear: not found

The shell would try to interpret that word as a command, and report back that it doesn't know any command by that name.

Also, to really make good use of shell scripts, you need to understand how to pass arguments to a script (44.15 ) and how to use some simple programming constructs (1.5 ) .