1 files changed, 50 insertions, 0 deletions
diff --git a/bin/rndl.sh b/bin/rndl.sh
new file mode 100644
index 00000000..18bcec07
--- /dev/null
+++ b/bin/rndl.sh
@@ -0,0 +1,50 @@
+# Print a random line from input
+self=rndl
+
+# If there are no arguments, we're checking stdin; this is more complicated
+# than checking file arguments because we have to count the lines in order to
+# correctly choose a random one, and two passes means we require a temporary
+# file if we don't want to read all of the input into memory (!)
+if [ "$#" -eq 0 ] ; then
+
+    # Create a temporary directory with name in $td, and handle POSIX-ish traps to
+    # remove it when the script exits.
+    td=
+    cleanup() {
+        [ -n "$td" ] && rm -fr -- "$td"
+        if [ "$1" != EXIT ] ; then
+            trap - "$1"
+            kill "-$1" "$$"
+        fi
+    }
+    for sig in EXIT HUP INT TERM ; do
+        # shellcheck disable=SC2064
+        trap "cleanup $sig" "$sig"
+    done
+    td=$(mktd "$self") || exit
+
+    # We'll operate on stdin in the temp directory; write the script's stdin to
+    # it with cat(1)
+    set -- "$td"/stdin
+    cat >"$td"/stdin
+fi
+
+# Count the number of lines in the input
+lc=$(sed -- '$=;d' "$@") || exit
+
+# If there were none, bail
+case $lc in
+    ''|0)
+        printf >&2 'rndl: No lines found on input\n'
+        exit 2
+        ;;
+esac
+
+# Try to get a random seed from rnds(1df) for rndi(1df)
+seed=$(rnds)
+
+# Get a random line number from rndi(1df)
+ri=$(rndi 1 "$lc" "$seed") || exit
+
+# Print the line using sed(1)
+sed -- "$ri"'!d' "$@"