[BUG] Inside .env file, a variable with literal value containing $ gets duplicated

[jvitor83]

Description

If you have a .env file with some variable containing $ in his value, the result duplicate the $ character.

As we define as literal, we expect it to be as-is.

Steps To Reproduce

# .env
SOME_VAR='MY OWN 1$'

# compose.yml
name: dollar-duplication
services:
  scratch:
    image: scratch
    environment:
      CONTAINER_ENV_VAR: "USE ${SOME_VAR}"

Execute:
docker compose config

Output:

name: dollar-duplication
services:
  scratch:
    environment:
      CONTAINER_ENV_VAR: USE MY OWN 1$$
    image: scratch
    networks:
      default: null
networks:
  default:
    name: dollar-duplication_default

Compose Version

Docker Compose version v2.30.3

Docker Environment

Client:
 Version:    26.1.1
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.14.0-desktop.1
    Path:     C:\Program Files\Docker\cli-plugins\docker-buildx.exe
  compose: Docker Compose (Docker Inc.)
    Version:  v2.27.0-desktop.2
    Path:     C:\Program Files\Docker\cli-plugins\docker-compose.exe
  debug: Get a shell into any image or container (Docker Inc.)
    Version:  0.0.29
    Path:     C:\Program Files\Docker\cli-plugins\docker-debug.exe
  dev: Docker Dev Environments (Docker Inc.)
    Version:  v0.1.2
    Path:     C:\Program Files\Docker\cli-plugins\docker-dev.exe
  extension: Manages Docker extensions (Docker Inc.)
    Version:  v0.2.23
    Path:     C:\Program Files\Docker\cli-plugins\docker-extension.exe
  feedback: Provide feedback, right in your terminal! (Docker Inc.)
    Version:  v1.0.4
    Path:     C:\Program Files\Docker\cli-plugins\docker-feedback.exe
  init: Creates Docker-related starter files for your project (Docker Inc.)
    Version:  v1.1.0
    Path:     C:\Program Files\Docker\cli-plugins\docker-init.exe
  sbom: View the packaged-based Software Bill Of Materials (SBOM) for an image (Anchore Inc.)
    Version:  0.6.0
    Path:     C:\Program Files\Docker\cli-plugins\docker-sbom.exe
  scout: Docker Scout (Docker Inc.)
    Version:  v1.8.0
    Path:     C:\Program Files\Docker\cli-plugins\docker-scout.exe

Server:
 Containers: 20
  Running: 19
  Paused: 0
  Stopped: 1
 Images: 70
 Server Version: 26.1.1
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 1
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local splunk syslog
 Swarm: inactive
 Runtimes: runc io.containerd.runc.v2
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: e377cd56a71523140ca6ae87e30244719194a521
 runc version: v1.1.12-0-g51d5e94
 init version: de40ad0
 Security Options:
  seccomp
   Profile: unconfined
 Kernel Version: 5.15.146.1-microsoft-standard-WSL2
 Operating System: Docker Desktop
 OSType: linux
 Architecture: x86_64
 CPUs: 8
 Total Memory: 8.732GiB
 Name: docker-desktop
 ID: 5150d74e-c0c0-446b-9828-3301461cb963
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 HTTP Proxy: http.docker.internal:3128
 HTTPS Proxy: http.docker.internal:3128
 No Proxy: hubproxy.docker.internal
 Labels:
  com.docker.desktop.address=npipe://\\.\pipe\docker_cli
 Experimental: false
 Insecure Registries:
  hubproxy.docker.internal:5555
  127.0.0.0/8
 Live Restore Enabled: false

WARNING: No blkio throttle.read_bps_device support
WARNING: No blkio throttle.write_bps_device support
WARNING: No blkio throttle.read_iops_device support
WARNING: No blkio throttle.write_iops_device support
WARNING: daemon is not using the default seccomp profile

Anything else?

No response

[PRITHIVEE]

Hi @jvitor83
The "$" after 1 is an escaping character for the "$" character present in you env
Without that the output's compose file will try to resolved a $ variable leading to unexpected behaviour

[jvitor83]

@PRITHIVEE i got that, but the single quote is supposed to treat the content as fully literal.

At least is what is in: https://docs.docker.com/compose/how-tos/environment-variables/variable-interpolation/#env-file-syntax

Single-quoted (') values are used literally.

• VAR='$OTHER' -> $OTHER
• VAR='${OTHER}' -> ${OTHER}

Anyway, I coudn't find a way to have only a single $ in the value!

[ndeloof]

The content is treated as fully literal, but then as you run docker compose config the resulting compose model is dumped, and $ is escaped to preserve this character from later interpolation by another compose command. This is the desired behavior

Please explain your use case, so I better understand why this is an issue for you and how you rely on config command.

[PRITHIVEE]

@jvitor83 access the env within the container, you wont be seeing the extra "$" when you access the env