Add command and change README to have some instructions

README.md

@@ -1,2 +1,19 @@
-# readydocker
-A macOS tool for starting then waiting for Docker.app to be ready
+# Ready Docker
+
+Ready Docker is a macOS tool for starting then waiting for Docker.app to be ready. It is designed to be used in environments where you want to bring up a container without human interaction.
+
+## Example Usage:
+
+```bash
+readydocker && docker-compose up -d
+```
+
+## Expectations
+
+- Docker should be located at /Applications/Docker.app
+- /tmp/ should be writable
+- docker command should be on $PATH
+
+## Install
+
+Place `readydocker` script in a folder on your $PATH.

readydocker

@@ -0,0 +1,92 @@
+#!/usr/bin/env bash
+
+###############################################################
+# Ready Docker
+###############################################################
+#
+# Ensure Docker.app is running and ready to bring containers up
+#
+# Designed to be used in environments where you want to bring
+# up a container without human interaction.
+#
+# Example Usage:
+#
+# readydocker && docker-compose up -d
+#
+# Expectations:
+#
+# - Docker should be located at /Applications/Docker.app
+# - /tmp/ should be writable
+# - docker command should be on $PATH
+
+##############################################################
+# Checks if another readydocker is running
+##############################################################
+lock_exists() { [[ -e /tmp/readydocker.lock ]]; }
+
+##############################################################
+# Adds lock
+##############################################################
+add_lock() { touch /tmp/readydocker.lock; }
+
+##############################################################
+# Removes a lock if it exists
+##############################################################
+remove_lock() {
+    if lock_exists ; then
+        rm /tmp/readydocker.lock
+    fi
+}
+
+###############################################################
+# Runs when the script exits but only if lock has been obtained
+###############################################################
+exit_script() {
+    remove_lock
+    # Clear trap
+    trap - SIGINT SIGTERM
+    kill -- -$$
+}
+
+##############################################################
+# Returns the status code of docker stats which will be 0
+# if successful
+##############################################################
+is_docker_ready() { docker stats --no-stream >/dev/null 2>&1; }
+
+# Check for another readydocker
+if lock_exists ; then
+    echo "Waiting for another readydocker process to release lock"
+
+    # Wait until another process has released the lock
+    while lock_exists ; do
+        echo -n "."
+        sleep 1
+    done
+
+    # Final newline
+    echo ""
+fi
+
+# Register traps
+trap exit_script SIGINT SIGTERM
+trap remove_lock EXIT
+
+# Adds lock to work with concurrent readydocker commands
+add_lock
+
+echo "Checking if Docker.app is ready"
+if ! is_docker_ready ; then
+    echo "Starting Docker.app"
+    open /Applications/Docker.app
+
+    while ! is_docker_ready ; do
+        echo -n "."
+        sleep 1
+    done
+
+    # Final newline
+    echo ""
+fi
+
+echo "Docker.app is ready"