plan9port adiff (https://plan9.io/sources/plan9/acme/bin/adiff)

adiff

#!/usr/local/plan9/bin/rc

. 9.rc
. $PLAN9/lib/acme.rc


if(~ $#* 0 1){
	echo >[1=2] usage: adiff file1 file2
	echo >[1=2] or adiff file1 file2... dir
	exit usage
}

newwindow

l=$1
r=$2
if (test -d $1) l=$1/`{basename $2}
if not if (test -d $2) r=$2/`{basename $1}

9 echo 'name '^`{pwd}^/-diff-^`{basename $l} | winwrite ctl

9 diff $* | 9 awk -v 'l='$l -v 'r='^$r '/^diff/ {l=$2; r=$3; next} /^[1-9]/ {sub("[acd]", " & " r ":"); sub("^", l ":", $0)}
	{print $0}' | winwrite body
winctl clean