Use vi if $EDITOR is unset.

hgmerge

@@ -1,81 +1,83 b''
 #!/bin/bash
 #
 # hgmerge - default merge helper for Mercurial
 #
 # This tries to find a way to do three-way merge on the current system.
 # The result ought to end up in $1.
 
 set -e # bail out quickly on failure
 
 LOCAL=$1
 BASE=$2
 OTHER=$3
 
+EDITOR="${EDITOR:-vi}"
+
 # Back up our file
 cp $LOCAL $LOCAL.orig
 
 # Attempt to do a non-interactive merge
 if which merge > /dev/null ; then
     if merge $LOCAL $BASE $OTHER 2> /dev/null; then
 	# success!
 	exit 0
     fi
     cp $LOCAL.orig $LOCAL
 elif which diff3 > /dev/null ; then
     if diff3 -m $LOCAL.orig $BASE $OTHER > $LOCAL ; then
 	# success
 	exit 0
     fi
     cp $LOCAL.orig $LOCAL
 fi
 
 if [ -n "$DISPLAY" ]; then
     # try using kdiff3, which is fairly nice
     if which kdiff3 > /dev/null ; then
 	if kdiff3 --auto $BASE $LOCAL $OTHER -o $LOCAL ; then
 	    exit 0
 	else
 	    exit 1
 	fi
     fi
 
     # try using tkdiff, which is a bit less sophisticated
     if which tkdiff > /dev/null ; then
 	if tkdiff $LOCAL $OTHER -a $BASE -o $LOCAL ; then
 	    exit 0
 	else
 	    exit 1
 	fi
     fi
 fi
 
 # Attempt to do a merge with $EDITOR
 if which merge > /dev/null ; then
     echo "conflicts detected in $LOCAL"
     merge $LOCAL $BASE $OTHER 2>/dev/null || $EDITOR $LOCAL
     exit 0
 fi
 
 if which diff3 > /dev/null ; then
     echo "conflicts detected in $LOCAL"
     diff3 -m $LOCAL.orig $BASE $OTHER > $LOCAL || $EDITOR $LOCAL
     exit 0
 fi
 
 # attempt to manually merge with diff and patch
 if which diff > /dev/null ; then
     if which patch > /dev/null ; then
 	T=`mktemp`
 	diff -u $BASE $OTHER > $T
 	if patch $LOCAL < $T ; then
 	    exit 0
 	else
 	    $EDITOR $LOCAL $LOCAL.rej
 	fi
 	rm $T
 	exit 1
     fi
 fi
 
 echo "hgmerge: unable to find merge, tkdiff, kdiff3, or diff+patch!"
 exit 1