Symbolic links

[Simon]

Sometimes it is convenient to have a file or directory in a certain place (e.g., because a script requires it to be there), but to point at a copy of that file or directory that exists elsewhere. This is sometimes a useful way to save space.

Let’s imagine we are building our own unit selection voice and we have several versions of the voice, each in its own directory, like this

Documents$ ls -l
total 0
drwxr-xr-x  2 simonk  staff  68 13 Mar 16:16 ss
drwxr-xr-x  2 simonk  staff  68 13 Mar 16:16 ss_domain
drwxr-xr-x  2 simonk  staff  68 13 Mar 16:17 ss_small
drwxr-xr-x  2 simonk  staff  68 13 Mar 16:16 ss_version_2

and that we want all of them to share some data. In the original voice that we made, in ss, there is the actual data in a directory called wav

Documents$ cd ss
ss$ ls -l
total 0
drwxr-xr-x  2 simonk  staff  68 13 Mar 16:18 wav
ss$ ls wav
arctic_a0001.wav arctic_a0006.wav
arctic_a0002.wav arctic_a0007.wav
arctic_a0003.wav arctic_a0008.wav
arctic_a0004.wav arctic_a0009.wav
arctic_a0005.wav arctic_a0010.wav

and we want it to look like there is also a wav directory with the same contents in each of the other voices, but without actually making a copy.

The way to do this is with a symbolic link. Let’s go into one of the other voices, which is currently empty

ss$ cd ../ss_version_2/
ss_version_2$ ls -l
ss_version_2$ 

now we make the symbolic link

ss_version_2$ ln -s ../ss/wav .

the link looks special when we examine it

ss_version_2$ ls -l
total 8
lrwxr-xr-x  1 simonk  staff  9 13 Mar 16:20 wav -> ../ss/wav

and in the Finder (or the equivalent on whatever operating system you are using) it will have a little arrow added to the icon

but it behaves just like it is a directory as far as any programs or scripts are concerned

for example we can cd in to it (on the command line or in the Finder) and take a look at the contents

ss_version_2$ cd wav
horizon:wav$ pwd
/Users/simonk/Documents/ss_version_2/wav
wav$ ls
arctic_a0001.wav arctic_a0006.wav
arctic_a0002.wav arctic_a0007.wav
arctic_a0003.wav arctic_a0008.wav
arctic_a0004.wav arctic_a0009.wav
arctic_a0005.wav arctic_a0010.wav

but any changes we make will also change the directory that we made the symbolic link to – they are the same thing.

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