#! /bin/sh
# Three-way file merge. 
# $Header: /usr/wft/RCS/SRC/RCS/merge,v 3.1 82/11/28 19:45:37 wft Exp $
# use: merge [-p] file1 file2 file3 [mark1 mark3]
# Effect: incorporates all changes that lead from file2 to file3 into file1.
# Result goes to std. output if -p is present, into file1 otherwise.
# Overlapping changes are delimited as follows:
# <<<<<<< file1
# lines in file1
# =======
# lines in file3
# >>>>>>> file3
# If mark1 and mark3 are given the delimiting lines <<<<.. and >>>>...
# contain mark1 and mark3 instead of the names of file1 and file3.
# A warning is printed if there are overlaps.

PATH=/bin:/usr/bin:.
DIFF3=/usr/lib/diff3
p=0
case $1 in
-p)
        p=$1
	shift;;
esac


if test $# -ge 3
then
        if test -f $1 -a -f $2 -a -f $3
        then
                trap "rm -f /tmp/d3[abc]$$" 0 1 2 13 15
                diff $1 $3 >/tmp/d3a$$
                diff $2 $3 >/tmp/d3b$$
                $DIFF3 -E /tmp/d3[ab]$$ $1 $2 $3 $4 $5 > /tmp/d3c$$
                r=$?
                if test $r != 0
                then
                        echo Warning: $r overlaps during merge. 1>&2
                fi
                if test $p != 0
                then
                        (cat /tmp/d3c$$; echo '1,$p') | ed - $1
                else
                        (cat /tmp/d3c$$; echo w) | ed - $1
                fi
                exit 0
        else
                echo "Cannot open $1, $2, or $3" 1>&2
        fi
fi
echo "usage: merge [-p] file1 file2 file3" 1>&2
exit 1