Issue 39580: Check for COMMAND_LINE_INSTALL variable in Python_Documentation.pkg

Hello Python developers!

I'm looking to deploy Python 3 silently to the Macs that I manage, so I can use Python for various scripts. I'm using Munki to accomplish this. However, the Python_Documentation.pkg subpackage includes this code in the postinstall script:

```
# make link in /Applications/Python m.n/ for Finder users
if [ -d "${APPDIR}" ]; then
    ln -fhs "${FWK_DOCDIR}/index.html" "${APPDIR}/Python Documentation.html"
    open "${APPDIR}" || true  # open the applications folder
fi
```

Would it be possible to test for the $COMMAND_LINE_INSTALL variable before opening a Finder window? If the $COMMAND_LINE_INSTALL exists, it'd be really great if it didn't open the Finder. This would allow me to silently deploy Python 3 without disrupting my users.

Thanks!

Mike

In case folks reading this are not aware, installer(8) sets an environmental variable COMMAND_LINE_INSTALL when an installation is triggered on the command line versus when a user double-clicks a package in the GUI to kick off the install.

I've filed the linked PR to add a test on the APPDIR open statement to avoid popping up the Finder when the package is installed on the command line. If there's a different method by which I should do this, please point me in the vague direction and I'm happy to update!

(note - I just signed the CLA today so it should be registered soonish)

Thanks for the PR! It looks reasonable but I do want to test it first on older macOS versions that we support before merging it. I'll do that before the next releases.

New changeset 966036af0e5e1dff8fedd423d90a246067537345 by Ned Deily in branch '3.7':
bpo-39580: add check for CLI installation on macOS
https://github.com/python/cpython/commit/966036af0e5e1dff8fedd423d90a246067537345

New changeset 5f190d2cc60cd82a604cbffb58b6ca8f40350a7a by Rick Heil in branch 'master':
bpo-39580: add check for CLI installation on macOS (GH-20271)
https://github.com/python/cpython/commit/5f190d2cc60cd82a604cbffb58b6ca8f40350a7a

New changeset 4564ebb1e62378d350d5483b0ae5d0d84082af2b by Miss Islington (bot) in branch '3.8':
bpo-39580: add check for CLI installation on macOS (GH-20271)
https://github.com/python/cpython/commit/4564ebb1e62378d350d5483b0ae5d0d84082af2b

New changeset bdc55eb55f7a88e374593dea1257566c2db3f5e4 by Miss Islington (bot) in branch '3.9':
bpo-39580: add check for CLI installation on macOS (GH-20271)
https://github.com/python/cpython/commit/bdc55eb55f7a88e374593dea1257566c2db3f5e4

Thanks again for the PR. The change will be included in python.org installers for macOS as of 3.9.0b4, 3.8.4, and 3.7.8.

stage: patch review -> resolved

pull_requests: + pull_request19551
stage: patch review