diff --git a/src/cmd/comm.c b/src/cmd/comm.c
new file mode 100644
index 0000000..8109c59
--- /dev/null
+++ b/src/cmd/comm.c
@@ -0,0 +1,178 @@
+#include <u.h>
+#include <libc.h>
+#include <bio.h>
+
+#define LB 2048
+int	one;
+int	two;
+int	three;
+
+char	*ldr[3];
+
+Biobuf *ib1;
+Biobuf *ib2;
+Biobuf *openfil(char*);
+int	rd(Biobuf*, char*);
+void	wr(char*, int);
+void	copy(Biobuf*, char*, int);
+int	compare(char*, char*);
+
+void
+main(int argc, char *argv[])
+{
+	int l;
+	char	lb1[LB],lb2[LB];
+
+	ldr[0] = "";
+	ldr[1] = "\t";
+	ldr[2] = "\t\t";
+	l = 2;
+	ARGBEGIN{
+	case '1':
+		if(!one) {
+			one = 1;
+			ldr[1][0] =
+			ldr[2][l--] = '\0';
+		}
+		break;
+
+	case '2':
+		if(!two) {
+			two = 1;
+			ldr[2][l--] = '\0';
+		}
+		break;
+
+	case '3':
+		three = 1;
+		break;
+
+	default:
+		goto Usage;
+
+	}ARGEND
+
+	if(argc < 2) {
+    Usage:
+		fprint(2, "usage: comm [-123] file1 file2\n");
+		exits("usage");
+	}
+
+	ib1 = openfil(argv[0]);
+	ib2 = openfil(argv[1]);
+
+
+	if(rd(ib1,lb1) < 0){
+		if(rd(ib2,lb2) < 0)
+			exits(0);
+		copy(ib2,lb2,2);
+	}
+	if(rd(ib2,lb2) < 0)
+		copy(ib1,lb1,1);
+
+	for(;;){
+		switch(compare(lb1,lb2)) {
+		case 0:
+			wr(lb1,3);
+			if(rd(ib1,lb1) < 0) {
+				if(rd(ib2,lb2) < 0)
+					exits(0);
+				copy(ib2,lb2,2);
+			}
+			if(rd(ib2,lb2) < 0)
+				copy(ib1,lb1,1);
+			continue;
+
+		case 1:
+			wr(lb1,1);
+			if(rd(ib1,lb1) < 0)
+				copy(ib2,lb2,2);
+			continue;
+
+		case 2:
+			wr(lb2,2);
+			if(rd(ib2,lb2) < 0)
+				copy(ib1,lb1,1);
+			continue;
+		}
+	}
+	exits(0);
+}
+
+int
+rd(Biobuf *file, char *buf)
+{
+	int i, c;
+
+	i = 0;
+	while((c = Bgetc(file)) != Beof) {
+		*buf = c;
+		if(c == '\n' || i > LB-2) {
+			*buf = '\0';
+			return 0;
+		}
+		i++;
+		buf++;
+	}
+	return -1;
+}
+
+void
+wr(char *str, int n)
+{
+
+	switch(n){
+		case 1:
+			if(one)
+				return;
+			break;
+
+		case 2:
+			if(two)
+				return;
+			break;
+
+		case 3:
+			if(three)
+				return;
+	}
+	print("%s%s\n", ldr[n-1],str);
+}
+
+void
+copy(Biobuf *ibuf, char *lbuf, int n)
+{
+	do
+		wr(lbuf,n);
+	while(rd(ibuf,lbuf) >= 0);
+	exits(0);
+}
+
+int
+compare(char *a, char *b)
+{
+	while(*a == *b){
+		if(*a == '\0')
+			return 0;
+		a++;
+		b++;
+	}
+	if(*a < *b)
+		return 1;
+	return 2;
+}
+
+Biobuf*
+openfil(char *s)
+{
+	Biobuf *b;
+
+	if(s[0]=='-' && s[1]==0)
+		s = "/fd/0";
+	b = Bopen(s, OREAD);
+	if(b)
+		return b;
+	fprint(2,"comm: cannot open %s: %r\n",s);
+	exits("open");
+	return 0;	/* shut up ken */
+}