run all commands at once using temporary shell script

README.md

@@ -30,9 +30,10 @@ Each change is a single YAML file with one or more shell commands that change in
     - gcloud iam service-accounts delete loadrunner
 
 A change must have at least a `do` section and optionally an `undo` section.
-The `do` section typically has a list of gcloud commands that create resources. Each line will be executed as a shell command so any available tool can be used.
+The `do` section typically has a list of gcloud commands that create resources but any available tool can be used.
+All lines will be executed at once using a single temporary shell script so you can use shell variables to simplify each section.
 The `undo` section typically has an ordered list of gcloud commands that deletes the same resources (in reverse order if relevant).
-Each command can use the following environment variables: `$PROJECT`,`$REGION`,`$ZONE` and any additional environment variables populated from the target configuration (see `env` section in the configuration below).
+Each command in each section can use the following environment variables: `$PROJECT`,`$REGION`,`$ZONE` and any additional environment variables populated from the target configuration (see `env` section in the configuration below).
 
 Information about the last applied change to a project is stored as a Google Storage Bucket object.
 

main.go

@@ -62,7 +62,7 @@ func newApp() *cli.App {
 		},
 		{
 			Name:  "up",
-			Usage: "Runs the do section of all pending migrations in order, one after the other.",
+			Usage: "Runs the do section of all pending migrations in order, one after the other. If a migration file is specified then stop after applying that one.",
 			Action: func(c *cli.Context) error {
 				defer started(c, "up = apply pending migrations")()
 				return cmdMigrationsUp(c)

migration.go

@@ -7,6 +7,7 @@ import (
 	"log"
 	"os"
 	"os/exec"
+	"path"
 	"path/filepath"
 	"sort"
 	"strings"
@@ -60,20 +61,33 @@ func (m Migration) ToYAML() ([]byte, error) {
 }
 
 // ExecuteAll the commands for this migration.
+// We create a temporary executable file with all commands.
+// This allows for using shell variables in multiple commands.
 func ExecuteAll(commands []string, envs []string) error {
 	if len(commands) == 0 {
 		return nil
 	}
-	for i, each := range commands {
-		log.Println(each)
-		cmd := exec.Command("sh", "-c", each)
-		cmd.Env = append(os.Environ(), envs...) // extend, not replace
-		cmd.Stdout = os.Stdout
-		cmd.Stderr = os.Stderr
-		err := cmd.Run()
-		if err != nil {
-			return fmt.Errorf("%d: failed to run :%v", i, err)
+	tempScript := path.Join(os.TempDir(), "gmig.sh")
+	content := new(bytes.Buffer)
+	fmt.Fprintln(content, `#!/bin/bash
+set -e -v`)
+	for _, each := range commands {
+		fmt.Fprintln(content, each)
+	}
+	if err := ioutil.WriteFile(tempScript, content.Bytes(), os.ModePerm); err != nil {
+		return fmt.Errorf("failed to write temporary migration section: %v", err)
+	}
+	defer func() {
+		if err := os.Remove(tempScript); err != nil {
+			log.Printf("warning: failed to remove temporary migration execution script:%s\n", tempScript)
 		}
+	}()
+	cmd := exec.Command("sh", "-c", tempScript)
+	cmd.Env = append(os.Environ(), envs...) // extend, not replace
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("failed to run migration section: %v", err)
 	}
 	return nil
 }