diffutils: Unified Format
2.2.2 Unified Format
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The unified output format is a variation on the context format that is
more compact because it omits redundant context lines. To select this
output format, use the '--unified[=LINES]' ('-U LINES'), or '-u' option.
The argument LINES is the number of lines of context to show. When it
is not given, it defaults to three.
In the early 1990s, only GNU 'diff' could produce this format and
only GNU 'patch' could automatically apply diffs in this format. For
proper operation, 'patch' typically needs at least three lines of
context.
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