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.\"     @(#)diff3.1	8.2 (Berkeley) 4/18/94
.\"
.Dd April 18, 1994
.Dt DIFF3 1
.Os BSD 4.3R
.Sh NAME
.Nm diff3
.Nd 3-way differential file comparison
.Sh SYNOPSIS
.Nm diff3
.Op Fl exEX3
.Ar file1 file2 file3
.Sh DESCRIPTION
The
.Nm diff3
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 Diff3
is used by
.Xr RCS 1
to merge specific versions or create
new versions.
.Pp
Options are:
.Bl -tag -width "--E, --X"
.It Fl e
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 file1 and file3.
In other words, the
.Fl e
option ignores differences specific to file1 and file2, and those
specific to file2 and file3.  It is useful for backing out changes
specific to file2 only.
.It Fl x
Produces an output script suitable for
.Xr ed 1
with changes
specific only to all three versions.
.It Fl 3
Produces an output script suitable for
.Xr ed 1
with changes
specific only to file3.
.It Fl E , 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.
.El
.Pp
The
.Fl E
option is used by
.Tn RCS
.Xr merge  1
to insure 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 file1 and file2.
Applying the edit script generated by the command
.Pp
.Dl diff3 -E file1 file2 file3
.Pp
to file1 results in the file:
.Pp
.Bd -literal -offset indent -compact
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 diff3
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 FILES
.Bl -tag -width /usr/bin/diff3 -compact
.It Pa /tmp/d3?????
temporary files.
.It Pa /usr/bin/diff3
the executable.
.El
.Sh SEE ALSO
.Xr diff 1
.Xr ed 1
.Xr rcs 1
.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.
.Sh HISTORY
A
.Nm
command appeared in
.At v7 .