Go to your SVN root, and then create a text file with any name. We’ll use “external.txt” for this example.

In your text file, tell SVN the folder and repository from with you want to fetch the code. The syntax is: folder svn_url. For this example, add the following line to your text file, with the directory name and the URL separated by whitespace: MYFOLDERA/library https://subversion.assembla.com/svn/your_assembla_space/trunk where “MYFOLDERA/library” creates a non-versioned folder called “library” under “MYFOLDERA”. It’s important to remember that there shouldn’t be another folder under “MYFOLDERA” called “library” or this step fails. The SVN path “.../your_assembla_space/trunk” is the source from which the files are fetched.

Set the property: svn propset svn:externals . -F external.txt 

The output should be property ‘svn:externals’ set on ‘.’

Run svn up  to see all of the files and folders under “trunk” fetched under MYFOLDERA/library.
​Note: Notice that under “trunk”, “MYFOLDERA/library” is also created along with any other externals you set.

Each time you want to fetch your changes, simply run svn up 

You can also use the svn:externals property to draw a subdirectory from a second repository. For this example, we’ll call it your_assembla_space_2. In this case, you can create a directory within the second repository by adding a second line to your text file: MYFOLDERB/library http://subversion.assembla.com/svn/your_assembla_space_2/trunk 

An externals definition can’t point to relative paths, such as .../../skins/myskin. It can point only to absolute URLs

The working copies created by the externals definition are not connected to the primary working copy, so to commit changes you’ve made in one or more external working copy, you must run svn commit explicitly on those working copies. In other words, committing on the primary working copy does not recurse into any external ones. 

Because externals definitions use absolute URLs, moving or copying a directory to which they are attached does not affect what gets checked out as an external working copy. But, the relative local target subdirectory does move with the renamed directory. For example, say that you use externals definitions on a directory in your /trunk which point to other areas of that line. Use svn copy to branch that line to a new location. For this example, we’ll use /branches/my-branch. The externals definitions on your new branch still refer to the resources in /trunk and not those same resources in /branches/my-branch.

If you need to re-parent your working copy (using svn switch --relocate ), then externals definitions are not also re-parented.