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(diff.info)Hunks

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Hunks
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   When comparing two files, `diff' finds sequences of lines common to
both files, interspersed with groups of differing lines called "hunks".
Comparing two identical files yields one sequence of common lines and
no hunks, because no lines differ.  Comparing two entirely different
files yields no common lines and one large hunk that contains all lines
of both files.  In general, there are many ways to match up lines
between two given files.  `diff' tries to minimize the total hunk size
by finding large sequences of common lines interspersed with small
hunks of differing lines.

   For example, suppose the file `F' contains the three lines `a', `b',
`c', and the file `G' contains the same three lines in reverse order
`c', `b', `a'.  If `diff' finds the line `c' as common, then the command
`diff F G' produces this output:

     1,2d0
     < a
     < b
     3a2,3
     > b
     > a

But if `diff' notices the common line `b' instead, it produces this
output:

     1c1
     < a
     ---
     > c
     3c3
     < c
     ---
     > a

It is also possible to find `a' as the common line.  `diff' does not
always find an optimal matching between the files; it takes shortcuts
to run faster.  But its output is usually close to the shortest
possible.  You can adjust this tradeoff with the `--minimal' option
(Note: diff Performance).