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Use the program diff3 to compare three files and
show any differences among them. (diff3 can also
merge files; see section Merging From
a Common Ancestor).
The ``normal'' diff3 output format shows each
hunk of differences without surrounding context. Hunks are
labeled depending on whether they are two-way or three-way, and
lines are annotated by their location in the input files.
See section Invoking diff3,
for more information on how to run diff3.
Here is a third sample file that will be used in examples to
illustrate the output of diff3 and how various
options can change it. The first two files are the same that we
used for diff (see section Two Sample Input Files). This is the
third sample file, called tao:
The Way that can be told of is not the eternal Way;
The name that can be named is not the eternal name.
The Nameless is the origin of Heaven and Earth;
The named is the mother of all things.
Therefore let there always be non-being, so we may see their
subtlety, And let there always be being, so we may see their
result. The two are the same, But after they are produced, they
have different names.
-- The Way of Lao-Tzu, tr. Wing-tsit Chan
Each hunk begins with a line marked ====.
Three-way hunks have plain ==== lines, and two-way
hunks have 1, 2, or 3
appended to specify which of the three input files differ in that
hunk. The hunks contain copies of two or three sets of input
lines each preceded by one or two commands identifying where the
lines came from.
Normally, two spaces precede each copy of an input line to
distinguish it from the commands. But with the -T or --initial-tab
option, diff3 uses a tab instead of two spaces; this
lines up tabs correctly. See section Preserving
Tabstop Alignment, for more information.
Commands take the following forms:
- file:la
This hunk appears after line l of file file,
and contains no lines in that file. To edit this file to
yield the other files, one must append hunk lines taken
from the other files. For example, 1:11a
means that the hunk follows line 11 in the first file and
contains no lines from that file.
-
file:rc
This hunk contains the lines in the range r of
file file. The range r is a
comma-separated pair of line numbers, or just one number
if the range is a singleton. To edit this file to yield
the other files, one must change the specified lines to
be the lines taken from the other files. For example, 2:11,13c
means that the hunk contains lines 11 through 13 from the
second file.
If the last line in a set of input lines is incomplete (see
section Incomplete Lines), it is
distinguished on output from a full line by a following line that
starts with \.
Groups of lines that differ in two or three of the input files
are called diff3 hunks, by analogy with diff
hunks (see section Hunks). If all
three input files differ in a diff3 hunk, the hunk
is called a three-way hunk; if just two input files
differ, it is a two-way hunk.
As with diff, several solutions are possible.
When comparing the files A, B, and C, diff3
normally finds diff3 hunks by merging the two-way
hunks output by the two commands diff A B and diff
A C. This does not necessarily minimize the size of the
output, but exceptions should be rare.
For example, suppose F contains the three lines a, b, f, G
contains the lines g, b, g,
and H contains the lines a, b, h. diff3
F G H might output the following:
====2
1:1c
3:1c
a
2:1c
g
====
1:3c
f
2:3c
g
3:3c
h
because it found a two-way hunk containing a in
the first and third files and g in the second file,
then the single line b common to all three files,
then a three-way hunk containing the last line of each file.
Here is the output of the command diff3 lao tzu tao
(see section A Third Sample Input File,
for the complete contents of the files). Notice that it shows
only the lines that are different among the three files.
====2
1:1,2c
3:1,2c
The Way that can be told of is not the eternal Way;
The name that can be named is not the eternal name.
2:0a
====1
1:4c
The Named is the mother of all things.
2:2,3c
3:4,5c
The named is the mother of all things.
====3
1:8c
2:7c
so we may see their outcome.
3:9c
so we may see their result.
====
1:11a
2:11,13c
They both may be called deep and profound.
Deeper and more profound,
The door of all subtleties!
3:13,14c
-- The Way of Lao-Tzu, tr. Wing-tsit Chan
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