Editing Patch (Unix) (section)

==Usage examples==
To create a patch, one could run the following command in a shell:
<syntaxhighlight lang="console">
$ diff -u oldFile newFile > mods.diff  # -u tells diff to output unified diff format
</syntaxhighlight>
To apply a patch, one could run the following command in a shell:

<syntaxhighlight lang="console">
$ patch < mods.diff
</syntaxhighlight>

This tells patch to apply the changes to the specified files described in <code>mods.diff</code>. Patches to files in subdirectories require the additional <code>-p''number''</code> option, where ''number'' is 1 if the base directory of the source tree is included in the diff, and 0 otherwise.

Patches can be undone, or reversed, with the '<code>-R</code>' option:

<syntaxhighlight lang="console">
$ patch -R < mods.diff
</syntaxhighlight>

In some cases when the file is not identical to the version the diff was generated against, the patch will not be able to be applied cleanly.  For example, if lines of text are inserted at the beginning, the line numbers referred to in the patch will be incorrect.  patch is able to recover from this, by looking at nearby lines to relocate the text to be patched.  It will also recover when lines of '''context''' (for context and unified diffs) are altered; this is described as '''fuzz'''.