diff --git a/.circleci/config.yml b/.circleci/config.yml
index 9a1e2c702..43fe490ea 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -100,6 +100,8 @@ jobs:
       - run: mkdir test_results
       - run:
           name: Run tests
+          environment:
+            test_env_var: test_env_var_value
           command: |
             C:\Users\circleci\go\bin\gotestsum.exe --junitfile test_results/windows.xml
       - store_test_results:
diff --git a/.circleci/pack.sh b/.circleci/pack
similarity index 100%
rename from .circleci/pack.sh
rename to .circleci/pack
diff --git a/.dockerignore b/.dockerignore
new file mode 100644
index 000000000..abea34be9
--- /dev/null
+++ b/.dockerignore
@@ -0,0 +1,4 @@
+.git
+Dockerfile*
+docker-compose*.yml
+.vagrant
diff --git a/.gitignore b/.gitignore
index fe774dfed..450328771 100644
--- a/.gitignore
+++ b/.gitignore
@@ -27,3 +27,6 @@ packrd/
 bin/golangci-lint
 integration_tests/tmp
 *.exe
+/issues
+/.vagrant
+/bash_history
diff --git a/Makefile b/Makefile
index f50603470..5a17e2da9 100644
--- a/Makefile
+++ b/Makefile
@@ -4,7 +4,7 @@ GOOS=$(shell go env GOOS)
 GOARCH=$(shell go env GOARCH)
 
 build: always
-	GO111MODULE=on .circleci/pack.sh
+	.circleci/pack
 	go build -o build/$(GOOS)/$(GOARCH)/circleci
 
 build-all: build/linux/amd64/circleci build/darwin/amd64/circleci
@@ -16,15 +16,15 @@ build/%/amd64/circleci: always
 clean:
 	GO111MODULE=off go clean -i
 	rm -rf build out docs dist
-	.circleci/pack.sh clean
+	.circleci/pack clean
 
 .PHONY: test
 test:
-	go test -v ./...
+	test_env_var=test_env_var_value go test -v ./...
 
 .PHONY: cover
 cover:
-	go test -race -coverprofile=coverage.txt ./...
+	test_env_var=test_env_var_value go test -race -coverprofile=coverage.txt ./...
 
 .PHONY: lint
 lint:
@@ -40,7 +40,7 @@ install-packr:
 
 .PHONY: pack
 pack:
-	bash .circleci/pack.sh
+	bash .circleci/pack
 
 .PHONY: install-lint
 install-lint:
diff --git a/Vagrantfile b/Vagrantfile
new file mode 100644
index 000000000..5a1d86399
--- /dev/null
+++ b/Vagrantfile
@@ -0,0 +1,18 @@
+# -*- mode: ruby -*-
+# vi: set ft=ruby :
+
+require 'etc'
+
+Vagrant.require_version ">= 2.0.0", "< 3.0.0"
+
+Vagrant.configure("2") do |config|
+  config.vm.box = "bento/ubuntu-20.04"
+
+  config.vm.provider "virtualbox" do |vb|
+    vb.memory = "2000"
+    vb.cpus = Etc.nprocessors
+  end
+
+  config.vm.synced_folder "~/.circleci", '/home/vagrant/.circleci'
+  config.vm.provision "shell", path: "bin/provision"
+end
diff --git a/bin/provision b/bin/provision
new file mode 100755
index 000000000..e95b452f2
--- /dev/null
+++ b/bin/provision
@@ -0,0 +1,62 @@
+#!/usr/bin/env bash
+
+apt_update() {
+  if [[ -z $apt_updated ]]
+  then
+    apt-get -qq update &&
+      apt_updated=true || exit
+  fi
+}
+
+if ! sudo -u vagrant docker run --rm hello-world
+then
+  apt_update &&
+    apt-get -qq install apt-transport-https ca-certificates curl software-properties-common &&
+    curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add - &&
+    add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu bionic stable" &&
+    apt-get -qq update &&
+    apt-get -qq install docker-ce &&
+    usermod -aG docker vagrant &&
+    sudo -u vagrant docker run --rm hello-world ||
+      exit
+fi
+
+if ! docker-compose --version
+then
+  curl --silent --show-error --fail --location \
+       "https://github.com/docker/compose/releases/download/1.27.4/docker-compose-$(uname -s)-$(uname -m)" \
+       -o /usr/local/bin/docker-compose &&
+    chmod +x /usr/local/bin/docker-compose &&
+    docker-compose --version ||
+      exit
+fi
+
+if ! grep '^cd /vagrant$' ~vagrant/.bashrc
+then
+  sudo -u vagrant <<<'cd /vagrant' tee -a ~vagrant/.bashrc ||
+    exit
+fi
+
+if ! grep '^HISTFILE=/vagrant/bash_history$' ~vagrant/.bashrc
+then
+  sudo -u vagrant tee -a <<<'HISTFILE=/vagrant/bash_history' ~vagrant/.bashrc ||
+    exit
+fi
+
+if ! sudo -u vagrant -i go version
+then
+  curl --silent --show-error --fail --location \
+       "https://golang.org/dl/go1.15.2.linux-amd64.tar.gz" |
+    tar -C /usr/local -xz &&
+    sudo -u vagrant tee -a <<<'export PATH=$PATH:/usr/local/go/bin' ~vagrant/.bash_profile &&
+    sudo -u vagrant -i go version ||
+      exit 1
+fi
+
+if ! dpkg-query -s build-essential
+then
+  apt_update &&
+    apt-get -qq install build-essential &&
+    dpkg-query -s build-essential ||
+      exit
+fi
diff --git a/local/local.go b/local/local.go
index 2141400d4..e21136b7f 100644
--- a/local/local.go
+++ b/local/local.go
@@ -10,6 +10,7 @@ import (
 	"path"
 	"regexp"
 	"syscall"
+	"strings"
 
 	"github.com/CircleCI-Public/circleci-cli/api"
 	"github.com/CircleCI-Public/circleci-cli/api/graphql"
@@ -41,7 +42,11 @@ func UpdateBuildAgent() error {
 
 func Execute(flags *pflag.FlagSet, cfg *settings.Config) error {
 
-	processedArgs, configPath := buildAgentArguments(flags)
+	processedArgs, configPath, err := buildAgentArguments(flags)
+	if err != nil {
+		return err
+	}
+
 	cl := graphql.NewClient(cfg.Host, cfg.Endpoint, cfg.Token, cfg.Debug)
 	configResponse, err := api.ConfigQuery(cl, configPath, pipeline.FabricatedValues())
 
@@ -87,7 +92,7 @@ func Execute(flags *pflag.FlagSet, cfg *settings.Config) error {
 	arguments := generateDockerCommand(processedConfigPath, image, pwd, processedArgs...)
 
 	if cfg.Debug {
-		_, err = fmt.Fprintf(os.Stderr, "Starting docker with args: %s", arguments)
+		_, err = fmt.Fprintf(os.Stderr, "Starting docker with args: %s\n", arguments)
 		if err != nil {
 			return err
 		}
@@ -97,6 +102,11 @@ func Execute(flags *pflag.FlagSet, cfg *settings.Config) error {
 		return errors.Wrap(err, "Could not find a `docker` executable on $PATH; please ensure that docker installed")
 	}
 
+	for _, e := range os.Environ() {
+		pair := strings.SplitN(e, "=", 2)
+		fmt.Fprintf(os.Stderr, "%s=%s\n", pair[0], pair[1])
+	}
+
 	err = syscall.Exec(dockerPath, arguments, os.Environ()) // #nosec
 	return errors.Wrap(err, "failed to execute docker")
 }
@@ -118,7 +128,7 @@ func AddFlagsForDocumentation(flags *pflag.FlagSet) {
 	flags.String("revision", "", "Git Revision")
 	flags.String("branch", "", "Git branch")
 	flags.String("repo-url", "", "Git Url")
-	flags.StringArrayP("env", "e", nil, "Set environment variables, e.g. `-e VAR=VAL`")
+	flags.StringArrayP("env", "e", nil, "Set environment variables, e.g. `-e VAR=VAL` or `-e VAR`")
 }
 
 // Given the full set of flags that were passed to this command, return the path
@@ -129,21 +139,33 @@ func AddFlagsForDocumentation(flags *pflag.FlagSet) {
 // GraphQL API, and feed the result of that into `build-agent`. The first step of
 // that process is to find the local path to the config file. This is supplied with
 // the `config` flag.
-func buildAgentArguments(flags *pflag.FlagSet) ([]string, string) {
+func buildAgentArguments(flags *pflag.FlagSet) ([]string, string, error) {
 
 	var result []string = []string{}
+	var outerErr error
 
 	// build a list of all supplied flags, that we will pass on to build-agent
 	flags.Visit(func(flag *pflag.Flag) {
 		if flag.Name != "config" && flag.Name != "debug" {
-			result = append(result, unparseFlag(flags, flag)...)
+			unparsedFlag, err := unparseFlag(flags, flag)
+
+			if err != nil {
+				outerErr = errors.Wrap(err, "Failed to build agent arguments")
+			}
+
+			result = append(result, unparsedFlag...)
 		}
 	})
+
+	if outerErr != nil {
+		return nil, "", outerErr
+	}
+
 	result = append(result, flags.Args()...)
 
 	configPath, _ := flags.GetString("config")
 
-	return result, configPath
+	return result, configPath, nil
 }
 
 func picardImage(output io.Writer) (string, error) {
@@ -302,7 +324,7 @@ func generateDockerCommand(configPath, image, pwd string, arguments ...string) [
 // Convert the given flag back into a list of strings suitable to be passed on
 // the command line to run docker.
 // https://github.com/CircleCI-Public/circleci-cli/issues/391
-func unparseFlag(flags *pflag.FlagSet, flag *pflag.Flag) []string {
+func unparseFlag(flags *pflag.FlagSet, flag *pflag.Flag) ([]string, error) {
 	flagName := "--" + flag.Name
 	result := []string{}
 	switch flag.Value.Type() {
@@ -310,10 +332,22 @@ func unparseFlag(flags *pflag.FlagSet, flag *pflag.Flag) []string {
 	// `--foo 1 --foo 2` will result in a single `foo` flag with an array of values.
 	case "stringArray":
 		for _, value := range flag.Value.(pflag.SliceValue).GetSlice() {
+			if flag.Name == "env" && ! strings.Contains(value, "=") {
+				// Bare env arg passed. Resolve from environment.
+				variableValue, ok := os.LookupEnv(value)
+				if !ok {
+					return nil, errors.New(fmt.Sprintf(
+						"Failed to resolve environment variable ‘%s’ in the environment.\n",
+						value,
+					))
+				} else {
+					value = fmt.Sprintf("%s=%s", value, variableValue)
+				}
+			}
 			result = append(result, flagName, value)
 		}
 	default:
 		result = append(result, flagName, flag.Value.String())
 	}
-	return result
+	return result, nil
 }
diff --git a/local/local_test.go b/local/local_test.go
index 7dc4b5e42..522f1ab3a 100644
--- a/local/local_test.go
+++ b/local/local_test.go
@@ -67,7 +67,7 @@ var _ = Describe("build", func() {
 			if testCase.expectedError != "" {
 				Expect(err).To(MatchError(testCase.expectedError))
 			}
-			args, configPath := buildAgentArguments(flags)
+			args, configPath, _ := buildAgentArguments(flags)
 			Expect(args).To(Equal(testCase.expectedArgs))
 			Expect(configPath).To(Equal(testCase.expectedConfigPath))
 
@@ -98,15 +98,21 @@ var _ = Describe("build", func() {
 			}),
 
 			Entry("many args, multiple envs", TestCase{
-				input:              []string{"--env", "foo", "--env", "bar", "--env", "baz"},
+				input:              []string{"--env", "foo=foo", "--env", "bar=bar", "--env", "baz=baz"},
 				expectedConfigPath: ".circleci/config.yml",
-				expectedArgs:       []string{"--env", "foo", "--env", "bar", "--env", "baz"},
+				expectedArgs:       []string{"--env", "foo=foo", "--env", "bar=bar", "--env", "baz=baz"},
 			}),
 
 			Entry("comma in env value (issue #440)", TestCase{
-				input:              []string{"--env", "{\"json\":[\"like\",\"value\"]}"},
+				input:              []string{"--env", "JSON={\"json\":[\"like\",\"value\"]}"},
 				expectedConfigPath: ".circleci/config.yml",
-				expectedArgs:       []string{"--env", "{\"json\":[\"like\",\"value\"]}"},
+				expectedArgs:       []string{"--env", "JSON={\"json\":[\"like\",\"value\"]}"},
+			}),
+
+			Entry("bare env value (issue #440)", TestCase{
+				input:              []string{"--env", "test_env_var"},
+				expectedConfigPath: ".circleci/config.yml",
+				expectedArgs:       []string{"--env", "test_env_var=test_env_var_value"},
 			}),
 
 			Entry("args that are not flags", TestCase{