symbolic link vs shell alias

In this post, we are learning differences and similarities between a symbolic link and a shell alias!

Photo by James Wainscoat on Unsplash

Since Python 2.x is retired, had to make command python point to Python 3.x in my OS. On a quick lookup, there were two solutions: one through creating a symbolic link and the other through a shell alias to a Python binary file. Which is a recommended way? Hence, clarifying it.

Question: What is a symbolic link and a shell alias?

Answer: A symbolic link, aka soft link or symlink, is a special kind of file that points to another file. A shell alias allows a string to be substituted for a word when it is used as the first word of a simple command.

Syntax for a symbolic link:

$ ln -s source_file myfile

The ln -s command creates the symbolic link.

Replace source_file with a name of an existing file across your OS’s filesystems for which you want to create the symbolic link.

Replace myfile with a name of a symbolic link.

Now you can use normal file management command such as cp , rm on the symbolic link.

Let’s see an example:

Currently, my folder structure looks like this:

Now I create a soft link to the file howdy.txt .

$ ln -s source_folder/howdy.txt joke_file

This creates a link named joke_file that points to the source_folder/howdy.txt . The folder structure now looks like this:

Now you can edit the joke_file . Any edits made in the file are reflected in the howdy.txt file. You can remove the joke_file using the rm command.

First let’s count number of lines in a joke_file and original howdy.txt . Then let’s add some more jokes in joke_file .

$ wc -l joke_file
5 joke_file
$ wc -l source_folder/howdy.txt
5 source_folder/howdy.txt

We see there are five lines in the files.

Let’s add another joke of 2 lines with 1 line for new line, so total 3 lines, to the joke_file and check line counts.

$ wc -l joke_file
8 joke_file
$ wc -l source_folder/howdy.txt
8 source_folder/howdy.txt

You can now check how jokes added to the joke_file is reflected to the howdy.txt file as well.

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You can remove the soft link using the command unlink <symbolic-link-name>.

$ ls -ltr
total 0
lrwxr-xr-x  1 dichha  staff   23 May 26 18:23 joke_file -> source_folder/howdy.txt
drwxr-xr-x  4 dichha  staff  128 May 26 18:07 source_folder
# unlink the symbolic link
$ unlink joke_file
# See the link is gone
$ ls -ltr
total 0
drwxr-xr-x  4 dichha  staff  128 May 26 18:07 source_folder
# Adding back the symbolic link
$ ln -s source_folder/howdy.txt joke_file

Now let’s make a file linked to be a script file so that it gives some dynamic result.

I have the joke_generator.py file under the source folder. Let’s create a symlink for it.

$ ln -s source_folder/joke_generator.py smiley

Now let’s look at the current file structure with tree . command.

See, we get a new symlink file named smiley . Let’s run the file.

$ smiley
Two antennas met on a roof, fell in love and got married.
The ceremony wasn't that much, but the reception was excellent.

It prints one of the jokes in the list. 😜

Let’s make this symlink smiley accessible in all shell session by putting it in .bash_profile .

PATH=<path-to-your-folder-where-symlink-lies>:${PATH}

Source your .bash_profile and now you can run smiley whenever wherever 🎵 in the bash shell you like!

Now let’s jump to shell alias.

Syntax for an alias:

$ alias name=value

The name is a name of the alias.

The value is a command line or a string.

Let’s see an example:

$ alias ll='ls -al'
$ ll
total 8
drwxr-xr-x   4 dichha  staff  128 May 25 23:51 .
drwxr-xr-x  16 dichha  staff  512 May 25 23:28 ..
-rw-r--r--   1 dichha  staff  181 May 25 23:50 joke_file
drwxr-xr-x   3 dichha  staff   96 May 25 23:49 source_folder

Here I named a command ls -al as ll . To make an alias permanent, you can add the alias in ~/.bash_profile for a login-shell. You can remove an alias using unalias <alias-name> .

Similarities:

Shell Alias and symbolic link both point to some other files.

Differences:

Shell Alias: is a shell specific command.

Symbolic link: almost a file, contains file location, on your filesystem. So if you move a file location, symbolic link is broken.

In conclusion, going a symbolic link route is a better solution in this case since its a reference to another file in a filesystem and not a shell specific.

That’s all for this post. I hope it was useful for your development. If you liked it, 👏 appreciated.

Congratulations on the completion! Thank you for reading.

There’s also another kind of alias, MacOS Finder.

Reference:

• ss64
• IU knowledge base