docs: migrate Docker instructions to relative bind mount

[MikeMcC399]

• supersedes docs: migrate Docker instructions to relative bind mount #374 (which I previously closed after waiting more than 2 months for a response)

Issue

The README > Run using Docker command example

docker run -v ${PWD}:/tmp:ro --rm -i ghcr.io/tcort/markdown-link-check:stable /tmp/README.md

uses PWD (Print Working Directory). The syntax ${PWD} can now be replaced by a simpler one using relative paths.

Relative paths

The Docker documentation for docker container run (with alias docker run) describes the option Mount volume (-v) using relative paths:

As of Docker Engine version 23, you can use relative paths on the host.

docker run -v ./content:/content -w /content -i -t ubuntu pwd

• Docker Engine 23.0.0 was released on Feb 1, 2023. The current version is
• Docker Engine 28.0.1 released on Feb 26, 2025.

Change

Use the relative path . syntax instead of ${PWD}:

docker run -v .:/tmp:ro --rm -i ghcr.io/tcort/markdown-link-check:stable /tmp/README.md

Verification

For example, under Ubuntu 24.04.2 LTS

git clone https://github.com/tcort/markdown-link-check
cd markdown-link-check
docker run -v .:/tmp:ro --rm -i ghcr.io/tcort/markdown-link-check:stable /tmp/README.md

Confirm that markdown-link-check runs successfully.

Logs

$ docker run -v .:/tmp:ro --rm -i ghcr.io/tcort/markdown-link-check:stable /tmp/README.md
Unable to find image 'ghcr.io/tcort/markdown-link-check:stable' locally
stable: Pulling from tcort/markdown-link-check
43c4264eed91: Pull complete
453ca8c35a67: Pull complete
7a291b8a7b57: Pull complete
15929fe50b42: Pull complete
c70efbd48e66: Pull complete
4f4fb700ef54: Pull complete
0e06fe306355: Pull complete
b28c781acdb5: Pull complete
5e49cffc8ea6: Pull complete
68f40888b8a2: Pull complete
Digest: sha256:b812aa72676ed310c045d2c89d56abc1f88dd06e68edbea982799a7ff01c8569
Status: Downloaded newer image for ghcr.io/tcort/markdown-link-check:stable

FILE: /tmp/README.md
  [✓] https://www.npmjs.com/package/isemail
  [✓] https://github.com/gaurav-nelson/github-action-markdown-link-check
  [✓] https://pre-commit.com
  [✓] https://megalinter.io/latest/
  [✓] https://megalinter.io/latest/descriptors/markdown_markdown_link_check/
  [✓] https://www.npmjs.com/package/ms
  [✓] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace#specifying_a_string_as_the_replacement
  [✓] https://github.com/tcort/markdown-link-check/blob/master/LICENSE.md
  [✓] https://github.com/tcort/markdown-link-check/actions/workflows/ci.yml/badge.svg

  9 links checked.

[BaseMax]

Dear Mike,

Thank you for your contribution. I see that your merge request is still in draft. Once it is ready for review, please let us know.

Many thanks.

[MikeMcC399]

Hopefully this minor improvement can be merged.

Using . instead of PWD tends to work better in a cross-platform environment including Windows with its different terminal window options.

[MikeMcC399]

@BaseMax

This PR seems to have stalled. Is there any reason it can't be merged? How many approvals do you need before merging?

[BaseMax]

Hi again. thank you so much.

Would you please explain a bit more? What is wrong with $PWD env var and why . and not $PWD?

https://www.docker.com/blog/best-way-learn-docker-free-play-docker-pwd/

https://stackoverflow.com/questions/43697810/meaning-of-pwd-path-to-directory

[MikeMcC399]

Hi @BaseMax

The articles that you refer to are quite old:

https://www.docker.com/blog/best-way-learn-docker-free-play-docker-pwd/ (July 2017)

https://stackoverflow.com/questions/43697810/meaning-of-pwd-path-to-directory (April 2017)

In February 2023 Docker introduced the ability to use the relative path . instead of $PWD. See the current Docker documentation:

https://docs.docker.com/reference/cli/docker/container/run/#volume

$PWD doesn't work well on Windows, although it is no problem on Linux.

The relative path . works on all operating systems.

If you prefer not to pick up this suggestion, it's fine. You can close this PR. Users can just refer themselves to Docker documentation.

Unrelated to markdown-link-check, I switch a lot between Docker Desktop on Ubuntu and Docker Desktop on Windows with WSL2, so the recommendation is based on my experience. I have written a lot of the documentation for Cypress Docker images using this syntax and there has been no feedback that it is bad or doesn't work.

[MikeMcC399]

I checked and in fact the relative path syntax . is only an advantage for Windows CMD terminal users. So that means it is only marginally better than the $PWD syntax. There is no difference on Ubuntu. Both work.

Windows terminals

Terminal	$PWD	.
Git Bash	fails	fails
CMD	fails	works
PowerShell	works	works

Ubuntu

Terminal	$PWD	.
Bash	works	works

[BaseMax]

@smainil
@WillGibson

[MikeMcC399]

@BaseMax

Thank you for the follow-up! I'm seeing 2 approvals now and no requests for change, so it looks like this could be merged.

[WillGibson]

I think we are deferring to @tcort because it's their project.

[BaseMax]

Thank you for your contribution.

[MikeMcC399]

@BaseMax

Thank you for your contribution.

Thank you also for the team's work to maintain this repo!