diffutils: Dry Runs
10.3.4 Predicting what 'patch' will do
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It may not be obvious in advance what 'patch' will do with a complicated
or poorly formatted patch. If you are concerned that the input might
cause 'patch' to modify the wrong files, you can use the '--dry-run'
option, which causes 'patch' to print the results of applying patches
without actually changing any files. You can then inspect the
diagnostics generated by the dry run to see whether 'patch' will modify
the files that you expect. If the patch does not do what you want, you
can modify the patch (or the other options to 'patch') and try another
dry run. Once you are satisfied with the proposed patch you can apply
it by invoking 'patch' as before, but this time without the '--dry-run'
option.
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