bin/free-port: Add new working utility

1 files changed, 73 insertions, 0 deletions

diff --git a/bin/free-port b/bin/free-port
new file mode 100755
index 0000000..2476b4b
--- /dev/null
+++ b/bin/free-port
@@ -0,0 +1,73 @@
+#!/bin/sh
+set -eu
+
+
+usage() {
+	cat <<-'EOF'
+		Usage:
+		  free-port
+		  free-port -h
+	EOF
+}
+
+help() {
+	cat <<-'EOF'
+
+
+		Options:
+		  -h, --help    show this message
+
+
+		Returns a free TCP port.
+
+
+		Examples:
+
+		  Get a port for a command:
+
+		    $ cmd -p `free-port`
+	EOF
+}
+
+
+for flag in "$@"; do
+	case "$flag" in
+		--)
+			break
+			;;
+		--help)
+			usage
+			help
+			exit
+			;;
+		*)
+			;;
+	esac
+done
+
+while getopts 'h' flag; do
+	case "$flag" in
+		h)
+			usage
+			help
+			exit
+			;;
+		*)
+			usage >&2
+			exit 2
+			;;
+	esac
+done
+shift $((OPTIND - 1))
+
+
+PORT=1024
+
+while true; do
+	if ! lsof -s TCP:LISTEN -i ":$PORT" >/dev/null; then
+		break
+	fi
+	PORT=$((PORT + 1))
+done
+
+echo "$PORT"