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Prepare distribution patches with gawk

Exploring the power and sophistication of awk.

I maintain GNU Awk. As part of making releases, I have to create a patch script to convert the file tree of the previous release into the current one. This means writing rm commands to remove any files that have been removed. This is fairly straightforward using tools like find, sort, and comm.

However, for the 4.1.2 release, I also changed the permissions (mode) on some files. I want to create chmod commands to update these files’ permission settings as well. This is a little harder, so I decided to write an awk script that will do this for me.

Let’s take a look at some of the sophistication and control you can achieve using awk, such as recursion, the use of arrays of arrays, and extension functions for using operating system facilities.

This script, comptrees.awk, uses the fts() extension function to do the heavy lifting. This function walks file trees, building up a representation of those trees using gawk‘s arrays of arrays.

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