add program to select random line from input...

Run time is number of lines, memory usage is max longest line, you
can't get better than this (though it's a bit slow because of how
it gets random values, and how often)..

randomline.sh

@@ -0,0 +1,44 @@
+#!/bin/sh -
+
+# Run time: O(number of lines)
+# Memory: O(longest line)
+
+# srand seed:
+# "dd if=/dev/random 2>/dev/null | LC_ALL=C tr -d -c 1-9 | dd bs=1 count=19 2>/dev/null" | getline seed; srand(seed)
+# + rand()
+
+LC_ALL=C awk '
+function urandom(n) {
+	# return random [0, n)
+
+	# maxn needs to be 2**(x*4), and cbs=x
+	maxn = 4294967296
+
+	if (n == 1)
+		return 0
+
+	if (n > maxn) {
+		printf("n too large!\n") > "/dev/stderr"
+		exit(5)
+	}
+
+	for (;;) {
+		"dd if=/dev/random | LC_ALL=C tr -c -d 0-9a-f | dd conv=unblock cbs=8" | getline a
+
+		r = ("0x" a) + 0
+		quot = int(maxn / n) * n
+		if (r >= quot)
+			continue
+
+		return r % n
+	}
+}
+
+{
+	#"jot -r 1 0 " (NR - 1) | getline a
+	a = urandom(NR)
+	#a = int(rand() * (NR))
+	if (a == 0)
+		save = $0
+}
+END { print save }'