Repeatable, idempotent ln

Say you create a soft link:

ln -s src target

If you try to repeat that same action, it will fail:

ln -s src target
# ln: failed to create symbolic link 'target': File exists

Adding -f will force the link to be overwritten:

ln -sf src target

This works for files, but what if src is a directory?

ln -sf src target
# .
# ├── src
# └── target -> src
ln -sf src target
# .
# ├── src
# │   └── src -> src
# └── target -> src

That's not correct! Since target resolves to a directory (src), the link gets created inside that directory.

This can be avoided with the -n flag:

-n, --no-dereference
treat LINK_NAME as a normal file if it is a symbolic link to a directory

NOTE: While the -T flag accomplishes a similar goal, it is not available on all systems. -n is most compatible.

Let's try again:

ln -sfn src target
# .
# ├── src
# └── target -> src
ln -sfn src target
# .
# ├── src
# └── target -> src

Therefore, for a truly idempotent and repeatable ln command, always use:

ln -sfn src target

NOTE: If the user has an existing file or link in the target location, it will be overwritten with this strategy!

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