symlink real world example

Question

I was reading php functions and I came across symlink but I really couldnt grab it specially its usage in real world application developement. Can anybody please explain me with real world example?

Thanks

Answer 1

Let's assume you have a src folder in your $HOME directory where your sources are stored. When you open a new shell, you usually enter your $HOME directory when the shell was started. It might be a common step that whenever you open up a new shell, you want to enter the directory ~/src/very_long_project_name afterwards.

This is where symlinks come into play: you could create a symlink in your $HOME directory (for example called vlpn that directly points to ~/src/very_long_project_name.

When you open your console next time, you could simply type cd vlpn instead of cd src/very_long_project_name. That's it. Nothing PHP specific. Like giraff and gnur already said.

Answer 2

An administrator may create symlinks to arrange storage without messing up filesystems; e.g. a web mirror may have thousands of sites hosted, and dozens of disks mounted:

/mnt/disk1/
/mnt/disk2/
...

and want to store data in their /var/www/htdocs/ without users caring about which disk holds their data.

/var/www/htdocs/debian -> /mnt/disk1/debian
/var/www/htdocs/ubuntu -> /mnt/disk2/ubuntu
/var/www/htdocs/centos -> /mnt/disk9/centos

Second, you may have a 'latest upload'; your users are uploading photos, or software packages, and you want http://example.com/HOT_STUFF to always be the most recent uploaded photo. You could set the symlink($new_upload, $HOT_STUFF); and users will never need more than the one URL to see the newest thing.

Third, Debian and Ubuntu use the update-alternatives mechanism to allow multiple versions of a tool to be installed at once and yet still allow the administrator to say which one is the default. e.g.,

$ ls -l /usr/bin/vi
lrwxrwxrwx 1 root root 20 2011-01-11 01:07 /usr/bin/vi -> /etc/alternatives/vi
$ ls -l /etc/alternatives/vi
lrwxrwxrwx 1 root root 18 2011-01-11 01:07 /etc/alternatives/vi -> /usr/bin/vim.basic
$ ls -l /usr/bin/vim.basic
-rwxr-xr-x 1 root root 1866904 2010-09-28 04:06 /usr/bin/vim.basic

It's a little circuitous, but the configuration is maintained in a per-system /etc/ directory, and the usual /usr/bin/vi path will execute something that is very much like vi, when there are many choices available (nvi, elvis, vim, AT&T vi, etc.)