View source for How to understand absolute and relative paths in Linux

= Absolute and Relative Paths =

In Linux there are two ways to address a file, (1) using a '''relative path''', and (2) using '''absolute path'''.

If you have a file in the subdirectory <code>my_data</code> and the file name is <code>my_test.dat</code>. 
Then you can use the absolute path
 /home/user.name/my_data/my_test.dat

This path is absolute, as it starts at the very top, <code>/</code>, the '''root directory'''.
Users on ARC do not have permissions to write to <code>/</code>, 
but they do have permissions to write to their own <code>/home/user.name/</code> home directory, 
and everything below it.

While it is '''very precise and clear''' when absolute paths are used, 
they '''tend to be long''' and also they really '''hard-wire the locations''' of the files 
to the specific directory and the directory cannot be moved easily to a different storage location without changing any references to it.


The '''relative paths''' can be really a convenient alternative, therefore. 
They are always '''relative to some other path'''. 

'''For example''', 
if a user just logged into his/her account the bash command line starts in the home directory, 
which is <code>/home/user.name</code>, therefore, the relative path to that file will be
 my_data/my_test.dat

if we change the command line to the directory <code>my_data</code>, then the relative path becomes simply
 my_test.dat


'''Please note''', that any path that starts with <code>/</code> is an '''absolute path''', by definition.


When using the command line, one can always check the '''current working directory''' of the session with the 
 $ pwd
command, that stands for '''Print Working Directory'''.

This way one can see '''the reference location''' for the relative file and directory names.

== Special Relative Paths ==

There are two very commonly used relative paths that have to be mentioned, <code>.</code>, the dot path, means '''this directory''', 
and the <code>..</code>, the double dot path, which means '''the parent directory''', or '''the directory above'''.


Thus, the <code>./my_test.dat</code> is fully equivalent to simply <code>my_test.dat</code>.

== Special Absolute Paths ==

The "<code>~</code>" (the tilda character) is used to point to '''the home directory'''. It is fully equivalent to the <code>/home/name.user/</code> path. The file from the example can also be referenced as
 ~/my_data/my_test.dat

= <code>rsync</code> and <code>scp</code> Remote Paths =

When we transfer files using <code>rsync</code> or <code>scp</code> commands, 
we provide the account details as <code>user.name@arc.ucalgary.ca</code>, 
which means, the user <code>user.name</code> on the computer <code>arc.ucalgary.ca</code>. 
Then the path follows after the "<code>:</code>" separator, 
but it always starts at the user's home location, therefore the path
 user.name@arc.ucalgary.ca:

simply means user's home directory. Clearly, the same directory can also be pointed as 
 user.name@arc.ucalgary.ca:/home/user.name/

but it is '''longer''', contains '''redundant''' information (the name is given twice), and it means '''exactly the same thing'''.

Naturally, the file <code>my_test.dat</code>, could be referenced, when using the relative path as
 user.name@arc.ucalgary.ca:my_data/my_test.dat

and using the absolute path as
 user.name@arc.ucalgary.ca:/home/user.name/my_data/my_test.dat

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