linux-absolute-directory-of-file

To obtain the full path of a file, we use
the readlink command. readlink
prints the absolute path of a symbolic link, but as a side-effect, it
also prints the absolute path for a relative path.

For example, suppose we have the following directory structure:

We use the -f flag to canonicalize the path of either a relative path
or a symbolic link. Therefore, if we change directory to
/home/example/, we can execute any of the following commands:

These commands will output:

In the case of the first command, readlink resolves the relative path
of foo/ to the absolute path of /home/example/foo/.

In the second case, readlink resolves the symbolic link of link/ to
the same absolute path.

For the final two commands, readlink canonicalizes the relative paths
and resolves to the same absolute path as the previous examples.

Note that the -f flag requires that all but the last component in the
supplied path — file.txt in our case — must exist. If the path does
not exist, no output is returned. For example, executing readlink -f
bar/file.txt will produce no output since the bar/ directory doesn’t
exist. In contrast, executing readlink -f  foo/other.txt will return
/home/example/foo/other.txt since all but the final component exists.

Instead, we can use the -m flag if we do not care if any of the
components in the supplied path exists. Likewise, we can use the -e
flag if we wish for all components in the supplied path to exist.

The second prerequisite is
the dirname command, which
prints the directory containing the supplied path.

If we supply a directory, dirname outputs the path containing that
directory. For example, we can execute:

This will produce:

Note that dirname prints the absolute directory because we supplied an
absolute path. If we changed directory to /home/ and executed dirname
example/foo/, dirname would output example. As a rule, if a
relative path is provided, dirname will output a relative directory,
and if an absolute path is provided, dirname will output an absolute
directory.

When supplying a file, dirname outputs the path containing that file.
For example, we can execute:

This will produce:

First, we can use the xargs
command, which converts input into arguments for a supplied command. By
piping the output from readlink into xargs and supplying the
command dirname as an argument to xargs, we can obtain this desired
absolute directory:

This results in:

Similarly, we can use
command
substitution — $(command) — where a command is executed in a
sub-shell, and the output from that command replaces its call.
Therefore, we can execute the following:

This command results in:

Equivalently, we could also execute the following command, and the
output would remain the same:

Note that command substitution works with bash, but will not
necessarily work with other shells.