Squash historical commits, leaving only the last 30 days of history, without harming the current worktree

git-squash-history.sh

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## Based on: https://gist.github.com/jonathanduke/020d97409396e784a2db84f178c8b907#file-git-squash-history-sh
## Public domain: http://unlicense.org/
## Modify as you wish, but you are encouraged to leave this comment for future reference in case the original is updated.
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# Use at your own risk! To make sure you know what you're doing, "origin" and "master" have been replaced with different names.
git checkout -B TEMPhead
git worktree add --checkout -B TEMPstart _TEMPworktree TEMPhead~30 # goes back 30 commits (or manually specify your own branch)
cd _TEMPworktree
git checkout --orphan TEMPnew # OR git checkout -B TEMPnew AND git reset --soft MYtarget # where "MYtarget" is the new base
git commit -m "Squashed history"
git cherry-pick TEMPstart..TEMPhead # assumes no other branches and merges are involved; otherwise do this manually
git branch -D TEMPstart
cd ..
git worktree remove _TEMPworktree
git checkout TEMPnew
git branch -D TEMPhead
git branch -M TEMPnew MYinitial # where "MYinitial" is the original branch we are squashing (probably master)
git push --force "MYremote" HEAD # where "MYremote" is the remote name (probably origin) and assumes HEAD to be where we started
git reflog expire --expire=now --all
git gc --prune=now
#git lfs prune # if using git-lfs, this will prune old versions of the file locally (not on the server)