Support "BackupFilenameExpand" option

cmd/backup/show_config.go

@@ -5,6 +5,7 @@ package main
 
 import (
 	"fmt"
+	"os"
 	"regexp"
 
 	"github.com/offen/docker-volume-backup/internal/errwrap"
@@ -22,6 +23,20 @@ func runShowConfig() error {
 			fmt.Println("source=<nil>\n<nil>")
 			continue
 		}
+		if config.BackupFilenameExpand {
+			unset, err := config.applyEnv()
+			if err != nil {
+				fmt.Printf("error applying env: %v\n", err) // print error to stdout for debugging
+				return errwrap.Wrap(err, "error applying env")
+			}
+			config.BackupFilename = os.ExpandEnv(config.BackupFilename)
+			config.BackupLatestSymlink = os.ExpandEnv(config.BackupLatestSymlink)
+			config.BackupPruningPrefix = os.ExpandEnv(config.BackupPruningPrefix)
+			if err := unset(); err != nil {
+				fmt.Printf("error unsetting env: %v\n", err) // print error to stdout for debugging
+				return errwrap.Wrap(err, "error unsetting environment variables")
+			}
+		}
 		// insert line breaks before each field name, assuming field names start with uppercase letters
 		formatted := regexp.MustCompile(`\s([A-Z])`).ReplaceAllString(fmt.Sprintf("%+v", *config), "\n$1")
 		fmt.Printf("source=%s\n%s\n", config.source, formatted)

test/show-config/docker-compose.yml

@@ -2,6 +2,9 @@ services:
   backup:
     image: offen/docker-volume-backup:${TEST_VERSION:-canary}
     environment:
+      BACKUP_FILENAME: "backup-$${BACKUP_TAG}.tar"
+      BACKUP_FILENAME_EXPAND: true
+      BACKUP_TAG: expanded
       BACKUP_SOURCES: /backup
       NOTIFICATION_URLS: "stdout://"
       AWS_S3_BUCKET_NAME: example-bucket

test/show-config/run.sh

@@ -22,6 +22,11 @@ if ! echo "$logs" | grep -q "BackupSources:/backup"; then
 fi
 pass "BACKUP_SOURCES present."
 
+if ! echo "$logs" | grep -q "BackupFilename:backup-expanded.tar"; then
+  fail "Missing expanded BACKUP_FILENAME in output."
+fi
+pass "Expanded BACKUP_FILENAME present."
+
 if ! echo "$logs" | grep -q "NotificationURLs:\[stdout://\]"; then
   fail "Missing NOTIFICATION_URLS in output."
 fi