A few times in the past, I’ve had the need to take a subdirectory of an
existing repository and move it to a new repository, while preserving
history. I always had to look up the syntax for
git filter-branch to
do this; it worked, but wasn’t very straightforward or easy to remember.
At some point, a
subtree split command was added to git that makes
this process much simpler.
My real-world use case was in the migration and modernization of our puppet installation. A local module for managing our Opsview installation was kept in the control repo. Over the years, our locally-maintained nagios plugins have grown to a point where they may be better maintained in a separate repository.
First, split the subdirectory into a separate branch:
sapphire:~/puppet/(puppet6=)$ git subtree split -P site/opsview/files/plugins -b nagios-plugins Created branch 'nagios-plugins' 6ffd1480866b514541a1ba711c85d79615211143
Create a new repository and pull that branch into it:
sapphire:~/puppet/(puppet6=)$ mkdir ~/noc-nagios-plugins sapphire:~/puppet/(puppet6=)$ ^mkdir^cd cd ~/noc-nagios-plugins sapphire:~/noc-nagios-plugins$ git init Initialized empty Git repository in /Users/jlavoie/noc-nagios-plugins/.git/ sapphire:~/noc-nagios-plugins/(main#)$ git pull ~/puppet nagios-plugins remote: Enumerating objects: 76, done. remote: Counting objects: 100% (76/76), done. remote: Compressing objects: 100% (61/61), done. remote: Total 76 (delta 24), reused 48 (delta 15), pack-reused 0 Unpacking objects: 100% (76/76), 239.51 KiB | 4.89 MiB/s, done. From /Users/jlavoie/puppet * branch nagios-plugins -> FETCH_HEAD
Push the new repository to the git server:
sapphire:~/noc-nagios-plugins/(main)$ git remote add origin email@example.com:/noc/nagios-plugins.git sapphire:~/noc-nagios-plugins/(main)$ git push -u origin main Initialized empty Git repository in /var/lib/gitolite3/repositories/noc/nagios-plugins.git/ Enumerating objects: 76, done. Counting objects: 100% (76/76), done. Delta compression using up to 12 threads Compressing objects: 100% (76/76), done. Writing objects: 100% (76/76), 233.39 KiB | 6.67 MiB/s, done. Total 76 (delta 26), reused 0 (delta 0), pack-reused 0 To git.bowdoin.edu:/noc/nagios-plugins.git * [new branch] main -> main Branch 'main' set up to track remote branch 'main' from 'origin'.
Clean up the old repo, deleting the temporary branch and associated files:
sapphire:~/noc-nagios-plugins/(main=)$ cd - /Users/jlavoie/puppet sapphire:~/puppet/(puppet6=)$ git br -D nagios-plugins Deleted branch nagios-plugins (was 6ffd148). sapphire:~/puppet/(puppet6=)$ git rm -r site/opsview/files/plugins/ rm 'site/opsview/files/plugins/check_bindhostname' rm 'site/opsview/files/plugins/check_cisco_bgp' rm 'site/opsview/files/plugins/check_cisco_nexus_cpu' [ ... more plugins ... ] sapphire:~/puppet/(puppet6+=)$ git commit -m 'migrate plugins to separate noc-nagios repo' [ ... pre-commit hooks ... ] [puppet6 0e70862] migrate plugins to separate noc-nagios repo 35 files changed, 19271 deletions(-) delete mode 100755 site/opsview/files/plugins/check_bindhostname delete mode 100755 site/opsview/files/plugins/check_cisco_bgp delete mode 100755 site/opsview/files/plugins/check_cisco_nexus_cpu [ ... more files ... ]