Intro To 'realpath' Command In Linux

2023-05-28 - By Robert Elder

     I use the 'realpath' command to obtain a unique representation of a file or directory path:

realpath svb.txt

Using 'realpath' To Canonicalize Paths

     If I run the 'realpath' command on this file path:

realpath /home/robert/important/svb.txt

     I'll get back the exact same path:

/home/robert/important/svb.txt

     However, if I use a slightly different path that refers to the same file:

realpath ../important/svb.txt

     I'll get back the original simplified file path:

/home/robert/important/svb.txt

     Here's another example that also returns the same path:

realpath ../important/./././svb.txt

/home/robert/important/svb.txt

Using 'realpath' With Symlinks

     If I create a symlink to this file and run the 'realpath' command on the symlink:

ln -s svb.txt other-bank.txt

ls -l

lrwxrwxrwx 1 robert robert    7 May 25 10:48 other-bank.txt -> svb.txt
-rw-rw-r-- 1 robert robert    0 May 25 10:46 svb.txt

     I'll once again get the original simplified absolute path:

realpath other-bank.txt

/home/robert/important/svb.txt

Using 'realpath' With Non-Existent Files

     There are many different flags that change the behavior of the 'realpath' command, such as the '-e':

realpath no-exist.txt

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

realpath -e no-exist.txt

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

     and '-m' flags:

realpath no-exist/other.txt

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

realpath -m no-exist/other.txt

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

     These flags control what happens if a path component doesn't exist.

Physical Vs. Logical Vs. Symlink

     There is also the '-P', and '-L and '-s' flags that control how symlink and relative path components are resolved.  If we start with the following collection of directories and files, some of which are symlinks:

ls -l worst

lrwxrwxrwx 1 robert robert 14 May 29 11:01 worst -> let-fail/other

ls -l worst/../failed-bank.txt

lrwxrwxrwx 1 robert robert 10 May 29 11:01 worst/../failed-bank.txt -> lehman.txt

ls -l failed-bank.txt

lrwxrwxrwx 1 robert robert 16 May 29 11:01 failed-bank.txt -> let-fail/svb.txt

     You an see how the 'realpath' command will return different values depending on which flags are used:

realpath -P worst/../failed-bank.txt

/home/robert/important/let-fail/lehman.txt

realpath -L worst/../failed-bank.txt

/home/robert/important/let-fail/svb.txt

realpath -s worst/../failed-bank.txt

/home/robert/important/failed-bank.txt

Obtaining Relative Paths With 'realpath'

     You can also use the relative to argument to obtain a path that's relative to a directory that you specify:

realpath --relative-to=/home/robert failed-bank.txt

important/let-fail/svb.txt

Setup Commands

     Here are the setup commands that were used in the creation of this article:

touch svb.txt
mkdir let-fail
mkdir let-fail/other
touch let-fail/svb.txt
touch let-fail/lehman.txt
ln -s let-fail/svb.txt failed-bank.txt
ln -s let-fail/other worst
ln -s lehman.txt let-fail/failed-bank.txt

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

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