Learning the bash Shell, Second Edition

A bash Debugger

In this section we’ll develop a basic debugger for bash. ^[121]Most debuggers have numerous sophisticated features that help a programmer in dissecting a program, but just about all of them include the ability to step through a running program, stop it at selected places, and examine the values of variables. These simple features are what we will concentrate on providing in our debugger. Specifically, we’ll provide the ability to:

• Specify places in the program at which to stop execution. These are called breakpoints.

• Execute a specified number of statements in the program. This is called stepping.

• Examine and change the state of the program during its execution. This includes being able to print out the values of variables and change them when the program is stopped at a breakpoint or after stepping.

• Print out the source code we are debugging along with indications of where breakpoints are and what line in the program we are currently executing.

• Provide the debugging capability without having to change the original source code of the program we wish to debug in any way.

As you will see, the capability to do all of these things (and more) is easily provided by the constructs and methods we have seen in previous chapters.

Structure of the Debugger

The bashdb debugger works by taking a shell script and turning it into a debugger for itself. It does this by concatenating debugger functionality and the target script, which we’ll call the guinea pig script, and storing it in ...