replace skip with more general drop

README.md

@@ -75,17 +75,21 @@ The "-x" option treats values as hex.
 	cbcbcb
 
 
-### skip: discard initial octets
+### drop: discard octets
 
-Throws away some initial octets from stdin,
+Throws away some octets from stdin,
 and sends the rest to stdout.
 
 You could use `dd` for the same purpose.
 
-	$ echo abcdefgh | dd skip=5 bs=1 status=none
+    $ echo 01234567 | drop 0 3
-	fgh
+	34567
-	$ echo abcdefgh | skip 5
+	$ echo 01234567 | drop 4 7
-	fgh
+	01237
+	$ echo 01234567 | drop 4 6
+	012367
+	$ echo 01234567 | drop 3 9999
+	012
 
 
 ### pcat: print text representation of pcap file

drop.c

@@ -0,0 +1,43 @@
+/*
+ * drop octets -- 2017 Neale Pickett <zephyr@dirtbags.net>
+ *
+ * This file is in the public domain.  I make no promises about the functionality
+ * of this program. 
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+int
+main(int argc, char *argv[])
+{
+	unsigned long int start;
+	unsigned long int end;
+	unsigned long int pos;
+
+	if (3 == argc) {
+		start = strtoul(argv[1], NULL, 0);
+		end = strtoul(argv[2], NULL, 0);
+	} else {
+		fprintf(stderr, "Usage: %s start end\n", argv[0]);
+		fprintf(stderr, "\n");
+		fprintf(stderr, "Drops octets from input\n");
+		return 1;
+	}
+
+	for (pos = 0; ; pos += 1) {
+		int c = getchar();
+
+		if (EOF == c) {
+			break;
+		}
+
+		if ((start <= pos) && (pos < end)) {
+			/* drop */
+		} else {
+			putchar(c);
+		}
+	}
+
+	return 0;
+}

skip.c

@@ -1,42 +0,0 @@
-/*
- * skip octets -- 2017 Neale Pickett <zephyr@dirtbags.net>
- *
- * This file is in the public domain.  I make no promises about the functionality
- * of this program. 
- */
-
-#include <stdio.h>
-#include <stdlib.h>
-
-int
-main(int argc, char *argv[])
-{
-	long int count;
-
-	if (argc != 2) {
-		fprintf(stderr, "Usage: %s count\n", argv[0]);
-		return 1;
-	}
-
-	count = strtol(argv[1], NULL, 0);
-	/* Throw away count octets */
-	for (; count > 0; count -= 1) {
-		int c = getchar();
-
-		if (EOF == c) {
-			break;
-		}
-	}
-
-	/* Spit out the rest */
-	while (1) {
-		int c = getchar();
-
-		if (EOF == c) {
-			break;
-		}
-		putchar(c);
-	}
-
-	return 0;
-}