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.\"     @(#)diff3.1	8.2 (Berkeley) 4/18/94
.\"
.Dd June 23, 2022
.Dt DIFF3 1
.Os
.Sh NAME
.Nm diff3
.Nd 3-way differential file comparison
.Sh SYNOPSIS
.Nm
.Op Fl 3AaEeimTXx
.Op Fl Fl diff-program Ar program
.Op Fl Fl strip-trailing-cr
.Op Fl L | Fl Fl label Ar label1
.Op Fl L | Fl Fl label Ar label2
.Op Fl L | Fl Fl label Ar label3
.Ar file1 file2 file3
.Nm
.Op Fl Fl help
.Op Fl Fl version
.Sh DESCRIPTION
The
.Nm
utility compares the contents of three different versions of a file,
.Ar file1 ,
.Ar file2
and
.Ar file3 ,
writing the result to the standard output.
The options describe different methods of merging and
purging
the separate versions into a new file.
.Nm
is used by
.Xr rcs 1
to merge specific versions or create
new versions.
.Pp
The options are as follows:
.Bl -tag -width "-E, -X"
.It Fl 3 , Fl Fl easy-only
Produces an output script suitable for
.Xr ed 1
with changes
specific only to
.Ar file3 .
.It Fl A Fl Fl show-all
Output all changes, bracketing conflicts.
.It Fl a , Fl Fl text
Treat all files as ASCII.
.It Fl E , Fl Fl show-overlap
.It Fl X
Similar to
.Fl e
and
.Fl x ,
respectively, but treat overlapping changes (i.e., changes that would
be noted with ==== in the normal listing) differently.
The overlapping lines from both files will be inserted by the edit script,
bracketed by "<<<<<<" and ">>>>>>" lines.
.It Fl e , Fl Fl ed
Produces output in a form suitable as an input script for the
.Xr ed 1
utility.
The script may then be used to merge differences common between all
three files and differences specific to
.Ar file1
and
.Ar file3 .
In other words, the
.Fl e
option ignores differences specific to
.Ar file1
and
.Ar file2 ,
and those specific to
.Ar file2
and
.Ar file3 .
It is useful for backing out changes specific to
.Ar file2
only.
.It Fl Fl help
Prints usage information and exits.
.It Fl i
Appends 'w' and 'q'
.Xr ed 1
commands.
.It Fl L , Fl Fl label
Defines labels to print instead of file names
.Ar file1 ,
.Ar file2
and
.Ar file3 .
.It Fl m, Fl Fl merge
Merge output instead of generating ed script.
.It Fl T, Fl Fl initial-tab
In the normal listing,
use a tab instead of two spaces
at the beginning of each line.
In modes that produce an
.Xr ed 1
script, this option changes nothing.
.It Fl x, Fl Fl overlap-only
Produces an output script suitable for
.Xr ed 1
with changes
specific only to all three versions.
.It Fl Fl diff-program Ar program
Use
.Ar program
instead of the default
.Xr diff 1
to compare files.
.It Fl Fl strip-trailing-cr
Strip trailing carriage return on input files.
.It Fl Fl version
Prints version information and exits.
.El
.Pp
The
.Fl E
option is used by
.Tn RCS
.Xr merge 1
to ensure that overlapping changes in the merged files are preserved
and brought to someone's attention.
.Pp
For example, suppose lines 7-8 are changed in both
.Ar file1
and
.Ar file2 .
Applying the edit script generated by the command
.Pp
.Dl $ diff3 -E file1 file2 file3
.Pp
to
.Ar file1
results in the file:
.Bd -literal -offset indent
lines 1-6
of file1
<<<<<<< file1
lines 7-8
of file1
=======
lines 7-8
of file3
>>>>>>> file3
rest of file1
.Ed
.Pp
The default output of
.Nm
makes notation of the differences between all files, and those
differences specific to each pair of files.
The changes are described by the commands necessary for
.Xr ed 1
to create the desired target from the different versions.
See
.Xr diff 1
for a description of the commands.
.Bl -tag -width "====="
.It Li \&====
The lines beneath this notation are ranges of lines which are different
between all files.
.It \&==== Ns Va n
The lines beneath this notation are ranges of lines which are exclusively
different in file
.Va n .
.El
.Sh SEE ALSO
.Xr diff 1 ,
.Xr ed 1 ,
.Xr merge 1 ,
.Xr rcs 1 ,
.Xr sdiff 1
.Sh HISTORY
A
.Nm
command appeared in
.At v7 .
.Sh BUGS
The
.Fl e
option cannot catch and change lines which have
.Ql \&.
as the first and only character on the line.
The resulting script will fail on that line
as
.Ql \&.
is an
.Xr ed 1
editing command.