Add in with-builder script

bin/with-builder.sh

@@ -0,0 +1,51 @@
+#!/bin/bash -eu
+
+# This script takes a command and executes it inside a container created with
+# the editor-api:builder image, allowing easy-ish updates to Gemfile.lock and
+# yarn.lock.
+
+cmd="$*"
+
+# The image we're working against
+image="editor-api:builder"
+
+# Files we copy in to the builder, and then out again.  These files are the
+# ones in the builder target of the Dockerfile.
+files="Gemfile Gemfile.lock"
+
+# Change to the repo root directory.
+cd $(dirname $0)/..
+
+function log() {
+	echo '>>> ' $*
+}
+
+# Container inside which we'll make our changes
+log "Creating new container from $image"
+builder=$(docker create -it $image $cmd)
+
+function cleanup () {
+	log "Removing $image container"
+	docker rm -f $builder || true
+}
+
+# Ensure our created container is removed on exit
+trap cleanup EXIT
+
+log "Copying files to $image container"
+for f in $files ; do
+	docker cp $f $builder:/app/
+done
+
+log "Starting $image container"
+docker start -ai $builder
+
+# Now the command has run, commit the changes, so that if we run this again,
+# we'll start from this point.
+log "Committing changes against the $image image"
+docker commit $builder $image
+
+log "Copying files back out of the $image container"
+for f in $files ; do
+	docker cp $builder:/app/$f $f
+done