Aliases vs Symbolic link - Lab 12.1

josepmaria

Lab 12.1 Deploying aliases suggests as solution

$ alias PROJECT ‘cd /home/staff/RandD/projects/projectX/src’

I wonder if the same result could have been achieved with a symbolic link

$ ln-s /home/staff/RandD/projects/projectX PROJECTsymboliclink

What is the difference between an alias and a Symbolic link?

Sincerely,

Josep Maria

KevinCSmallwood

You are correct that the end result would be the same in this situation of using the above alias and the above symbolic link. Name something you want to do, and we can probably come up with at least 5 different ways to do it. The thing is, in practice, what is the best way for you to use?

Again, we are talking about:

An alias:
$ alias PROJECT ‘cd /home/staff/RandD/projects/projectX/src’
and a symbolic link:
$ ln -s /home/staff/RandD/projects/projectX/src ~/PROJECT # I altered your line a little

First off, to use the alias, we can be anywhere in the filesystem. We could be in /tmp, for example and just type:

$ pwd            # Print Working Directory
/tmp
$ PROJECT     # The alias is a command that changes your working directory
$ pwd
/home/staff/RanD/projects/projectX/src

So, by executing the alias, PROJECT, you have changed your working directory from wherever you were to where the alias changed your working directory to be. The thing is an alias can be any command that you wanted it to be. It could have been something that a developer/programmer may have found useful like:

$ alias PROJECT 'cd /home/staff/RandD/projects/projectX/src; make all; make install'

Beyond the scope of this class, the "make" command is used to run commands (from a "Makefile") that usually does things like compiles programs and installs binaries into system directories. Like I said way beyond the scope of this class, but something fitting a project source directory. So, an alias is a command (or set of commands) that you are creating a "short-cut" for. It is much easier for you to type "PROJECT" rather than "cd /home/staff/RandD/projects/projectX/src; make all; make install" in the above example. This is especially true if you are typing the command many, many times during the day or week.

A symbolic link is a special file in your filesystem. It, too, is a "short-cut" for a filesystem reference, but it doesn't allow you to execute commands. It "symbolically" "points" (sorry for all the quotes) to something in the filesystem. So, going back to the original example and your question:

$ ln -s /home/staff/RandD/projects/projectX/src ~/PROJECT

This creates a special file in the filesystem located in your $HOME or login directory (~) called PROJECT. If you use this file name in various commands, it is the same as if you used what it points to (with certain exceptions):

$ cd /home/staff             # or ~ in this case
$ ls PROJECT                    # since you are in ~, you are referencing the file PROJECT in your $HOME directory
<results of an "ls" of /home/staff/RandD/projects/projectX/src>
$ cd /tmp
$ pwd
/tmp
$ ls PROJECT
<probably something along the lines of "file not found" unless there just happened to be a /tmp/PROJECT file>
$ cd ~/PROJECT               # this would be the equivalence of the alias, but note that you have to type the command
$ pwd
/home/staff/RandD/projects/projectX/src
$ 

So, again, you can essentially use either, but the alias is a command, and the symbolic link is a special file in the filesystem that points to something.

josepmaria

@KevinCSmallwood thank you for your time and valuable explanations.
Your answer is a true master class. I really appreciate it.

Now I understand the difference between aliases and symbolic links.

Sincerely,
Josep Maria