This GitHub Action can be used in a workflow to install Cygwin.

e.g.

- run: git config --global core.autocrlf input

- uses: actions/checkout@v2

- uses: cygwin/cygwin-install-action@master

- run: bash tests/script.sh  # see footnote [1]

Please fix my terrible cargo-cult PowerShell.

If you're going to use actions/checkout in your workflow, you should precede that with

- run: git config --global core.autocrlf input

to ensure that any shell scripts etc. in your repository don't get checked out with \r\n line endings (leading to '\r': command not found errors).

Likewise, if you have multiple lines of shell script in a YAML block for run: in your workflow file, the file this is written into on the runner ends up with \r\n line endings.

You can use >- (rather than |) to ensure that it doesn't contain any newlines.

Alternatively, you can also use:

• igncr in the SHELLOPTS environment variable
• invoke bash with -o igncr

By default, this action prepends Cygwin's /usr/bin directory to the PATH.

However, if you want to ensure that PATH only contains Cygwin executables, and other stuff installed in the VM image isn't going to get picked up:

• Set PATH to something like /usr/bin:$(cygpath ${SYSTEMROOT})/system32 in your shell script

or,

• Put CYGWIN_NOWINPATH=1 into the environment
• start a login shell with bash --login
• because the profile script from does cd ${HOME}, either:
  • cd ${GITHUB_WORKSPACE} in your shell script, or
  • prevent the profile script from changing directory by putting CHERE_INVOKING into the environment

If you want the opposite – the system PATH to remain unchanged by this action – add add-to-path: false to the action settings.

Cygwin's setup creates Cygwin-style symlinks by default, and some executables (e.g. python) are symlinks.

Since CMD and PowerShell don't understand those symlinks, you cannot run those executables directly in a run: in your workflow. Execute them via bash or env instead.

Alternatively, putting e.g. CYGWIN=winsymlinks:native into the workflow's environment works, since setup now honours that.

You probably don't need to change the setting for site, and you shouldn't change check-sig unless you're very confident it's appropriate and necessary. These options are very unlikely to be useful except in some very isolated circumstances, such as using the Cygwin Time Machine.

[1] The Workflow documentation suggests you should also use bash options -eo pipefail, omitted here for clarity