src/libmp/port/reduce - plan9 - Git at Google

 O=$1
 shift
 objtype=$1
 shift

 nl='
 '
 reduce="("`ls -p ../$objtype/*.[cs] 2>/dev/null | sed 's/..$//' | sed 's/^.*\///' | tr "$nl" '|' | sed 's/.$//'`")"

 echo $* | tr ' ' "$nl" | egrep -v $reduce | tr "$nl" ' '
	O=$1
	shift
	objtype=$1
	shift

	nl='
	'
	reduce="("`ls -p ../$objtype/.[cs] 2>/dev/null \| sed 's/..$//' \| sed 's/^.\///' \| tr "$nl" '\|' \| sed 's/.$//'`")"

	echo $* \| tr ' ' "$nl" \| egrep -v $reduce \| tr "$nl" ' '