Intro To 'dirname' Command In Linux

2023-12-13 - By Robert Elder

I use the 'dirname' command to extract the leading path components from a file or directory path:

dirname /home/robert/todo.txt

/home/robert

dirname /home/robert/my-directory

/home/robert

Relative & Absolute Paths

In this example, the 'dirname' command extracts the directory part from the relative or absolute path of the image file:

dirname robert/subdir/cat.png

robert/subdir

dirname /home/robert/cat.png

/home/robert

Works With Directories

If the full path ends with a directory, the 'dirname' command extracts the enclosing directory:

dirname /home/robert/backups

/home/robert

dirname /home/robert/backups/

/home/robert

Extract Multiple Directories At Once

You can pass multiple arguments to the 'dirname' command, to extract the leading path components of all arguments:

dirname /home/robert/cat.png /home/mike/dog.png /home/sally/rat.png

/home/robert
/home/mike
/home/sally

The 'dirname' Vs. 'basename' Commands

According to the info pages, the 'basename' and 'dirname' commands are related in the following way:

info dirname

...
   Together, ‘basename’ and ‘dirname’ are designed such that if ‘ls
"$name"’ succeeds, then the command sequence ‘cd "$(dirname "$name")";
ls "$(basename "$name")"’ will, too.  This works for everything except
file names containing a trailing newline.
...

To put the above paragraph into practice, we can say that if the following 'ls' command succeeds:

name=/home/robert/cat.png
ls "$name"

Then these commands should also succeed:

cd "$(dirname "$name")"
ls "$(basename "$name")"

In other words, if this command succeeds:

ls "/home/robert/cat.png"

these commands should also succeed:

cd "$(dirname "/home/robert/cat.png")"
ls "$(basename "/home/robert/cat.png")"

and, equivalently, these commands should too:

cd "/home/robert/"
ls "cat.png"

Works With Non-existant Files & Symlinks

The dirname command is not affected by symlinks or whether a file actually exists or not, as illustrated by the following examples:

mkdir first-directory
mkdir first-directory/subdir/
touch first-directory/subdir/foo.txt
ln -s first-directory second-directory

ls -l

total 4
drwxrwxr-x 3 robert robert 4096 Nov 20 15:19 first-directory
lrwxrwxrwx 1 robert robert   15 Nov 20 15:19 second-directory -> first-directory

ls -l first-directory

total 4
drwxrwxr-x 2 robert robert 4096 Nov 20 15:19 subdir

ls -l first-directory/subdir

total 0
-rw-rw-r-- 1 robert robert 0 Nov 20 15:19 foo.txt

dirname first-directory/subdir/foo.txt

first-directory/subdir

dirname second-directory/subdir/foo.txt

second-directory/subdir

rm -r first-directory/subdir

dirname first-directory/subdir/foo.txt

first-directory/subdir

dirname second-directory/subdir/foo.txt

second-directory/subdir

Implementation

The GNU Core Utils version of the 'dirname' command simply performs strings operations to print the first part of the file path.

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

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