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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
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
output is large, you might want
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 behavior.
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,
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. This makes
diff run faster, but
occasionally it may produce non-minimal output. The --horizon-lines=lines
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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