diff runs quite efficiently; however, in some circumstances
you can cause it to run faster or produce a more compact set of changes.
There are two ways that you can affect the performance of GNU
diff by changing the way it compares files.
Performance has more than one dimension. These options improve one aspect of performance at the cost of another, or they improve performance in some cases while hurting it in others.
The way that GNU
diff determines which lines have changed always
comes up with a near-minimal set of differences. Usually it is good
enough for practical purposes. If the
diff output is large, you
diff to use a modified algorithm that sometimes
produces a smaller set of differences. The `-d' or
`--minimal' option does this; however, it can also cause
diff to run more slowly than usual, so it is not the default
When the files you are comparing are large and have small groups of
changes scattered throughout them, you can use the `-H' or
`--speed-large-files' option to make a different modification to
the algorithm that
diff uses. If the input files have a constant
small density of changes, this option speeds up the comparisons without
changing the output. If not,
diff might produce a larger set of
differences; however, the output will still be correct.
diff discards the prefix and suffix that is common to
both files before it attempts to find a minimal set of differences.
diff run faster, but occasionally it may produce
non-minimal output. The `--horizon-lines=lines' option
diff from discarding the last lines lines of the
prefix and the first lines lines of the suffix. This gives
diff further opportunities to find a minimal output.
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