Question

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Is [---] a comment in Git such that I can use only % tool=opendiff % once in my .gitconfig?

Answer 1

I think you are asking whether the square bracket syntax in .gitconfig means something significant. The answer is yes, it separates .gitconfig into sections. Each section has a name, shown between the square brackets. For example:

[core]
        repositoryformatversion = 0
        filemode = true
        bare = false

In the above example, the section name is core. If you change the word core to something else, Git won’t be able to find, for example, the bare option because it needs to be inside the core section.

The git-config(1) manual page has a whole section describing the format of the configuration file.