Practical UNIX

Debugging Your Script

If a script doesn’t do what you expect, or if a variable doesn’t seem to have the value you think it should, you can do a couple things to debug the problem. The easiest is to use the -x option to the Bourne shell. You can do this by modifying the first line of your script to look like this:

#!/bin/sh -x

Or, you can run the shell directly on your script with the -x option, like this:

sh -x scriptname

Debug Info Goes to Standard Error The shell -x option outputs the commands being executed to standard error. To page this output, do this: sh -x scriptname >&2 | pg To save it in a file, enter this: sh -x scriptname >&2 |tee filename

Both methods accomplish the same thing; the shell is instructed to print each line in the ...