ref: acde9cddfda6e49d5093c6deee0076c6415d6ded
dir: /testdir/T.system/
echo T.system: test system built-in
awk=${awk-../a.out}
rm -f foo
$awk 'BEGIN {
n = system("exit 3")
print n
exit n+1
}
' >foo
echo $? >>foo
echo "3
4" >foo1
diff foo foo1 || echo 'BAD: T.system (1)'