The Easy Way™
It turns out that this is such a common and useful practice that the overlords of Git made it really easy, but you have to have a newer version of Git (>= 1.7.11 May 2012). See the appendix for how to install the latest Git. Also, there's a real-world example in the walkthrough below.
Prepare the old repo
cd <big-repo>
git subtree split -P <name-of-folder> -b <name-of-new-branch>
Note: <name-of-folder> must NOT contain leading or trailing characters. For instance, the folder named subproject MUST be passed as subproject, NOT ./subproject/
Note for Windows users: When your folder depth is > 1, <name-of-folder> must have *nix style folder separator (/). For instance, the folder named path1\path2\subproject MUST be passed as path1/path2/subproject
Create the new repo
mkdir ~/<new-repo> && cd ~/<new-repo>
git init
git pull </path/to/big-repo> <name-of-new-branch>
Link the new repo to GitHub or wherever
git remote add origin <git@github.com:user/new-repo.git>
git push -u origin master
Cleanup inside <big-repo>, if desired
git rm -rf <name-of-folder>
Note: This leaves all the historical references in the repository. See the Appendix below if you're actually concerned about having committed a password or you need to decreasing the file size of your .git folder.
Walkthrough
These are the same steps as above, but following my exact steps for my repository instead of using <meta-named-things>.
Here's a project I have for implementing JavaScript browser modules in node:
tree ~/node-browser-compat
node-browser-compat
├── ArrayBuffer
├── Audio
├── Blob
├── FormData
├── atob
├── btoa
├── location
└── navigator
I want to split out a single folder, btoa, into a separate Git repository
cd ~/node-browser-compat/
git subtree split -P btoa -b btoa-only
I now have a new branch, btoa-only, that only has commits for btoa and I want to create a new repository.
mkdir ~/btoa/ && cd ~/btoa/
git init
git pull ~/node-browser-compat btoa-only
Next, I create a new repo on GitHub or Bitbucket, or whatever and add it as the origin
git remote add origin git@github.com:node-browser-compat/btoa.git
git push -u origin master
Happy day!
Note: If you created a repo with a README.md, .gitignore and LICENSE, you will need to pull first:
git pull origin master
git push origin master
Lastly, I'll want to remove the folder from the bigger repo
git rm -rf btoa
Appendix
Latest Git on macOS
To get the latest version of Git using Homebrew:
brew install git
Latest Git on Ubuntu
sudo apt-get update
sudo apt-get install git
git --version
If that doesn't work (you have a very old version of Ubuntu), try
sudo add-apt-repository ppa:git-core/ppa
sudo apt-get update
sudo apt-get install git
If that still doesn't work, try
sudo chmod +x /usr/share/doc/git/contrib/subtree/git-subtree.sh
sudo ln -s \
/usr/share/doc/git/contrib/subtree/git-subtree.sh \
/usr/lib/git-core/git-subtree
Thanks to rui.araujo from the comments.
Clearing your history
By default removing files from Git doesn't actually remove them, it just commits that they aren't there anymore. If you want to actually remove the historical references (i.e. you committed a password), you need to do this:
git filter-branch --prune-empty --tree-filter 'rm -rf <name-of-folder>' HEAD
After that, you can check that your file or folder no longer shows up in the Git history at all
git log -- <name-of-folder> # should show nothing
However, you can't "push" deletes to GitHub and the like. If you try, you'll get an error and you'll have to git pull before you can git push - and then you're back to having everything in your history.
So if you want to delete history from the "origin" - meaning to delete it from GitHub, Bitbucket, etc - you'll need to delete the repo and re-push a pruned copy of the repo. But wait - there's more! - if you're really concerned about getting rid of a password or something like that you'll need to prune the backup (see below).
Making .git smaller
The aforementioned delete history command still leaves behind a bunch of backup files - because Git is all too kind in helping you to not ruin your repo by accident. It will eventually delete orphaned files over the days and months, but it leaves them there for a while in case you realize that you accidentally deleted something you didn't want to.
So if you really want to empty the trash to reduce the clone size of a repo immediately you have to do all of this really weird stuff:
rm -rf .git/refs/original/ && \
git reflog expire --all && \
git gc --aggressive --prune=now
git reflog expire --all --expire-unreachable=0
git repack -A -d
git prune
That said, I'd recommend not performing these steps unless you know that you need to - just in case you did prune the wrong subdirectory, y'know? The backup files shouldn't get cloned when you push the repo, they'll just be in your local copy.
Credit
Option A:
git clone git@github.com:whatever folder-name
Ergo, for right here use:
git clone git@github.com:whatever .
Option B:
Move the .git folder, too. Note that the .git folder is hidden in most graphical file explorers, so be sure to show hidden files.
mv /where/it/is/right/now/* /where/I/want/it/
mv /where/it/is/right/now/.* /where/I/want/it/
The first line grabs all normal files, the second line grabs dot-files. It is also possibe to do it in one line by enabling dotglob (i.e. shopt -s dotglob) but that is probably a bad solution if you are asking the question this answer answers.
Better yet:
Keep your working copy somewhere else, and create a symbolic link. Like this:
ln -s /where/it/is/right/now /the/path/I/want/to/use
For your case this would be something like:
ln -sfn /opt/projectA/prod/public /httpdocs/public
Which easily could be changed to test if you wanted it, i.e.:
ln -sfn /opt/projectA/test/public /httpdocs/public
without moving files around. Added -fn in case someone is copying these lines (-f is force, -n avoid some often unwanted interactions with already and non-existing links).
If you just want it to work, use Option A, if someone else is going to look at what you have done, use Option C.
Best Answer
With the Multiple SCMs Plugin:
create a different repository entry for each repository you need to checkout (main project or dependancy project.
for each project, in the "advanced" menu (the second "advanced" menu, there are two buttons labeled "advanced" for each repository), find the "Local subdirectory for repo (optional)" textfield. You can specify there the subdirectory in the "workspace" directory where you want to copy the project to. You could map the filesystem of my development computer.
The "second advanced menu" doesn't exist anymore, instead what needs to be done is use the "Add" button (on the "Additional Behaviours" section), and choose "Check out to a sub-directory"
Hope that helps.