Intro To 'readlink' Command In Linux

2024-01-17 - By Robert Elder

I use the 'readlink' command to canonicalize a file or directory path:

ls -l

total 0
-rw-rw-r-- 1 robert robert  0 Jan 12 18:15 config_2023-12-25.txt
lrwxrwxrwx 1 robert robert 21 Jan 12 18:15 master-config.txt -> config_2023-12-25.txt

readlink master-config.txt

config_2023-12-25.txt

Default Behaviour Of 'readlink'

If I run the 'readlink' command on a symbolic link, I'll see the target that the symbolic link points to, and the return code will indicate success:

readlink master-config.txt

config_2023-12-25.txt

echo $?

However, if I run the readlink command on a regular file, I won't see any output, and the return code will indicate failure:

readlink config_2023-12-25.txt

(no output)

echo $?

Readlink Mode

By default, the 'readlink' command runs in so-called 'Readlink mode':

info readlink

...
‘Readlink mode’

     ‘readlink’ outputs the value of the given symbolic links.  If
     ‘readlink’ is invoked with an argument other than the name of a
     symbolic link, it produces no output and exits with a nonzero exit
     code.
...

This mode is intended to only be run on symbolic links, and will return an error code otherwise.

Canonicalization Mode

The readlink command also supports other flags that activate so-called "Canonicalization mode", which prints absolute file paths:

info readlink

‘Canonicalize mode’

     ‘readlink’ outputs the absolute name of the given files which
     contain no ‘.’, ‘..’ components nor any repeated separators (‘/’)
     or symbolic links.  Note the ‘realpath’ command is the preferred
     command to use for canonicalization.  *Note realpath invocation::.

In fact, according to the 'readlink' command's own documentation, the 'realpath' command is preferred over the 'readlink' command for canonicalization of file paths:

info readlink

Note the ‘realpath’ command is the preferred command to use for canonicalization.

Flags That Use Canonicalization Mode

"Canonicalization mode" behaves just like the 'realpath' command and is activated by several flags, such as the '-f' flag:

readlink -f no-exist.txt

/home/robert/important/no-exist.txt

echo $?

realpath no-exist.txt

/home/robert/important/no-exist.txt

echo $?

the '-e' flag

readlink -e no-exist.txt

(no output)

echo $?

realpath -e no-exist.txt

realpath: no-exist.txt: No such file or directory

echo $?

and '-m' flag:

readlink -m no-exist/other.txt

/home/robert/important/no-exist/other.txt

echo $?

realpath -m no-exist/other.txt

/home/robert/important/no-exist/other.txt

echo $?

And that's why the 'readlink' command is my favourite Linux command.

Intro To 'stty' Command In Linux Published 2023-10-04	$1.00 CAD Terminal Block Mining Simulation Game	Intro To 'nproc' Command In Linux Published 2023-07-15	Intro To 'comm' Command In Linux Published 2023-09-06
How To Force The 'true' Command To Return 'false' Published 2023-07-09	A Surprisingly Common Mistake Involving Wildcards & The Find Command Published 2020-01-21	A Guide to Recording 660FPS Video On A $6 Raspberry Pi Camera Published 2019-08-01	Intro To 'chroot' Command In Linux Published 2023-06-23

Why Bother Subscribing?

Free Software/Engineering Content. I publish all of my educational content publicly for free so everybody can make use of it. Why bother signing up for a paid 'course', when you can just sign up for this email list?
Read about cool new products that I'm building. How do I make money? Glad you asked! You'll get some emails with examples of things that I sell. You might even get some business ideas of your own :)
People actually like this email list. I know that sounds crazy, because who actually subscribes to email lists these days, right? Well, some do, and if you end up not liking it, I give you permission to unsubscribe and mark it as spam.