bash Cookbook

Running Any Executable

Problem

You need to run a command on a Linux or Unix system.

Solution

Use bash and type the name of the command at the prompt.

$someprog

Discussion

This seems rather simple, and in a way it is, but a lot goes on behind the scenes that you never see. What’s important to understand about bash is that its basic operation is to load and execute programs. All the rest is just window dressing to get ready to run programs. Sure there are shell variables and control statements for looping and if/then/else branching, and there are ways to control input and output, but they are all icing on the cake of program execution.

So where does it get the program to run?

bash will use a shell variable called $PATH to locate your executable. The $PATH variable is a list of directories. The directories are separated by colons (:). bash will search in each of those directories for a file with the name that you specified. The order of the directories is important—bash looks at the order in which the directories are listed in the variable, and takes the first executable found.

$ echo $PATH
/bin:/usr/bin:/usr/local/bin:.
$

In the $PATH variable shown above, four directories are included. The last directory in that list is just a single dot (called the dot directory, or just dot), which represents the current directory. The dot is the name of the directory found within every directory on a Linux or Unix file system—wherever you are, that’s the directory to which dot refers. For example, when ...