Make Qshell Clean Up After Itself
December 18, 2002 Timothy Prickett Morgan
Hey, Ted:
I’ve written a Qshell script that creates some work files that are needed only for the duration of the script. I want the script to delete them before it ends. Here’s the problem: There are several places where the script can end normally and plenty of places where execution of the script could end abnormally. In CL, I’d use a goto command to branch to an end-of-job routine, where I could put commands to clean up, but Qshell does not have a goto command.
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I never thought I’d wish for a goto command, but I do. Do you have any suggestions?
— Dave
Qshell doesn’t have a goto command, but it does have other mechanisms for handling tasks that goto handles in other languages.
In this case, you should trap the EXIT event. Traps are asynchronous monitors. That is, they take over whenever something happens. The EXIT event happens when the script ends.
The following short script creates two work files. The $$ special variable returns the process ID. Placing the process ID within a file name is a good way to create work files that other jobs will not bother. A process ID is an integer number. If the process ID is 8406, for example, the work files will be named temp.1.8406 and temp.2.8406. When the script ends, the EXIT trap kicks in and runs the rm command to delete the work files.
trap 'rm *.$$' EXIT > temp.1.$$ > temp.2.$$ ls temp.*.* exit
For another example of how to use a trap, see the article, “Tracing a Qshell Variable,” which published in the June 19 issue of Midrange Guru, OS/400 Edition.
— Ted
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