home-manager: add support for custom backup command (#6424) #7153
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This adds a new backupCommand option to allow users to specify a custom command to run on existing files during activation, as an alternative to the existing backupFileExtension mechanism. Adds backupCommand option to NixOS and nix-darwin modules. Exports HOME_MANAGER_BACKUP_COMMAND environment variable when set. Updates file activation logic to use the custom backup command if provided, falling back to the existing backup extension logic. Updates collision checking and user-facing instructions to mention the new option. This enables advanced backup workflows, such as moving files to trash or archiving with custom tools, before managing them with Home Manager.
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That looks very good! I think this should have been done a long time ago. |
khaneliman
reviewed
Jun 8, 2025
| run mv $VERBOSE_ARG "$targetPath" "$backup" || errorEcho "Moving '$targetPath' failed!" | ||
| if [[ -e "$targetPath" && ! -L "$targetPath" ]] ; then | ||
| if [[ -n "$HOME_MANAGER_BACKUP_COMMAND" ]] ; then | ||
| # TODO: Bail out early? |
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Curious what you mean by bail out early? We should continue on to the link creation.
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I was thinking about the case in which the backup command failed, for whatever reason, but still removed the original file. However, upon second reading, it appears that's not necessary. Suppose the file is deleted without being backed up. In that case, it is lost anyway, and I suppose it is the user's responsibility to ensure that they select a reliable backup command that will fail gracefully. So I think this comment can be removed.
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Description
This PR adds support for a custom backup command in Home Manager.
A new
backupCommandoption is introduced, allowing users to specify a shell command to run on existing files that would otherwise block activation (e.g., moving files to trash, archiving, or custom backup logic). If set, this command is used in preference to the existingbackupFileExtensionmechanism.backupCommandoption to NixOS and nix-darwin modules.HOME_MANAGER_BACKUP_COMMANDenvironment variable when set.This enables more flexible and user-defined backup workflows during Home Manager activations.
This resolves Optional user defined script for error handling in case of home-manager backup file already existing #6424.
Checklist
Change is backwards compatible.
backupCommand, or the new environment variableHOME_MANAGER_BACKUP_COMMANDis used.Code formatted.
Code tested.
Test cases updated/added. See example.
Commit messages formatted.
If this PR adds a new module...
. N/A
Maintainer CC
N/A