To debug a bash script and to know what the environment is where a script is behaving it is convenient to log. This is what I added to my e-mail prosessing script yesterday. It is simple and of course every one else could think of it. Probably it is invented hundreds of times. Here's my solution.

The script starts with a call to check_logdir(). This function checks if the LOG_DIR exists. If it exists it adds a seperation line. This is because the if has to have a command in the then section. But it is also convenient because you have a seperation line between script calls.
Then there is the log function. The log function accepts two parameters. One is the prompt, the other is a string to be concatenated to the prompt. Handy for listing parameter-values.
But you could also do a logging of only one line. For example the last line.

The logging can be enabled or disabled by commenting/uncommenting the proper line of: