buildkite-agent env has --from-env-file and --print flags

clicommand/env.go

@@ -1,9 +1,12 @@
 package clicommand
 
 import (
+	"bufio"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"os"
+	"strconv"
 	"strings"
 
 	"github.com/urfave/cli"
@@ -32,20 +35,41 @@ var EnvCommand = cli.Command{
 			Usage:  "Pretty print the JSON output",
 			EnvVar: "BUILDKITE_AGENT_ENV_PRETTY",
 		},
+		cli.BoolFlag{
+			Name:  "from-env-file",
+			Usage: "Source environment from file described by $BUILDKITE_ENV_FILE",
+		},
+		cli.StringFlag{
+			Name:  "print",
+			Usage: "Print a single environment variable by `NAME` as raw text followed by a newline",
+		},
 	},
 	Action: func(c *cli.Context) error {
-		env := os.Environ()
-		envMap := make(map[string]string, len(env))
+		var envMap map[string]string
+		var err error
 
-		for _, e := range env {
-			k, v, _ := strings.Cut(e, "=")
-			envMap[k] = v
+		if c.Bool("from-env-file") {
+			envMap, err = loadEnvFile(os.Getenv("BUILDKITE_ENV_FILE"))
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "Error loading BUILDKITE_ENV_FILE: %v\n", err)
+				os.Exit(1)
+			}
+		} else {
+			env := os.Environ()
+			envMap = make(map[string]string, len(env))
+
+			for _, e := range env {
+				k, v, _ := strings.Cut(e, "=")
+				envMap[k] = v
+			}
 		}
 
-		var (
-			envJSON []byte
-			err     error
-		)
+		if name := c.String("print"); name != "" {
+			fmt.Println(envMap[name])
+			return nil
+		}
+
+		var envJSON []byte
 
 		if c.Bool("pretty") {
 			envJSON, err = json.MarshalIndent(envMap, "", "  ")
@@ -69,3 +93,42 @@ var EnvCommand = cli.Command{
 		return nil
 	},
 }
+
+func loadEnvFile(path string) (map[string]string, error) {
+	envMap := make(map[string]string)
+
+	if path == "" {
+		return nil, errors.New("no path specified")
+	}
+
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+
+	scanner := bufio.NewScanner(f)
+
+	lineNo := 0
+	for scanner.Scan() {
+		lineNo++
+
+		line := scanner.Text()
+		if line == "" {
+			continue
+		}
+
+		name, quotedValue, ok := strings.Cut(line, "=")
+		if !ok {
+			return nil, fmt.Errorf("Unexpected format in %s:%d", path, lineNo)
+		}
+
+		value, err := strconv.Unquote(quotedValue)
+		if err != nil {
+			return nil, fmt.Errorf("unquoting value in %s:%d: %w", path, lineNo, err)
+		}
+
+		envMap[name] = value
+	}
+
+	return envMap, nil
+}

clicommand/env_test.go

@@ -0,0 +1,42 @@
+package clicommand
+
+import (
+	"fmt"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestLoadEnvFile(t *testing.T) {
+	f, err := os.CreateTemp("", t.Name())
+	if err != nil {
+		t.Error(err)
+	}
+	data := map[string]string{
+		"HELLO": "world",
+		"FOO":   "bar\n\"bar\"\n`black hat`\r\n$(have you any root)",
+	}
+	for name, value := range data {
+		fmt.Fprintf(f, "%s=%q\n", name, value)
+	}
+
+	result, err := loadEnvFile(f.Name())
+	require.NoError(t, err)
+
+	assert.Equal(t, data, result, "data should round-trip via env file")
+}
+
+func TestLoadEnvFileQuotingError(t *testing.T) {
+	f, err := os.CreateTemp("", t.Name())
+	require.NoError(t, err)
+
+	fmt.Fprintf(f, "%s=%q\n", "ONE", "ok")
+	fmt.Fprintln(f, "TWO=missing quotes")
+
+	result, err := loadEnvFile(f.Name())
+	assert.Nil(t, result)
+
+	assert.Equal(t, `unquoting value in `+f.Name()+`:2: invalid syntax`, err.Error())
+}