I moved your stuff but don't freak out cuz I left behind a symlink

Saturday, June 29, 2013

Learning new nix-craft is kinda like being handed shiny new electronics. You're instantly intrigued with what new stuff you can do with it. This entry is the first in a series about nix-craft.

I'm not sure when I first heard of symlinking, but the first time it hit me as "something I should get acquainted with" was while I was reading dotfiles.github.io. Context clues provided me with the idea that to symlink was to leave a little note to your OS about where you moved the file it expected to find there.

So, as I had endeavored to clean my virtual $HOME of dotfiles, it became apparent that I needed to get familiar with symlinks.

Leaving a note

To create a symlink, you'd type this into your terminal:

ln -s path/to/target path/to/link

In English, this reads as: Create a symlink at path/to/link that redirects to path/to/target.

Reading the note

Most programs play nicely with symlinks. For instance, if you were to symlink your ~/.vimrc to ~/dotfiles/vim/.vimrc, Vim would access ~/.vimrc but would end up reading from ~/dotfiles/vim/.vimrc instead. It's kind of like a HTTP 302 that redirects you to another URI, or in our case, another path on your filesystem. Microsoft Windows users might find symlinks to be similar to shortcuts. They're essentially the same thing with the caveat that Windows programs would unfortunately get cranky if you tried to pass the shortcut file as an executable file. In *nix systems, symlinks in place of the actual file is okay for the most part!

It's also helpful to know what path your existing symlinks are pointing to. A simple ls doesn't list out your symlinks. You'll want to run ls -l, and symlinks will look something like the second entry below:

-rw-------   1 sitong  staff    28054 Jun 29 17:52 .viminfo
lrwxr-xr-x   1 sitong  staff       33 Jun 29 16:57 .vimrc -> /Users/sitong/dotfiles/vim/.vimrc

I actually ran ls -al since the symlinks in my $HOME are all dotfiles.

Removing the note

Removing the symlink is just an rm to the symlink. For instance:

rm ~/.vimrc

A little bonus

So we saw that ln -s is the command for symlinks but what if you passed a naked ln command to your terminal?

You would actually be creating a hard link. Hard links point directly to a file's memory space instead of a filesystem path as with symlinks. This means you can move or rename the target file and the hard link will still resolve to that original target file. If you were to move or rename your symlinked target file then when some program tries to resolve the symlink, it won't find anything at that path. Try it out yourself!


[*nix-craft] [dotfiles] [shellscript]