lfs-book/appendixa/patch-desc.xml

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<sect2><title>Short description</title>

<para><command>patch</command> modifies files according to a patch file.
A patch file normally is a difference listing created with the diff program.
By applying these differences to the original files, patch creates the patched
versions. Using patches instead a entire new tarballs to keep your sources
up-to-date can save you a lot of download time.</para>

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