Working with Linux

The ls subshell returns the files and folders in the current directory and the ls from outside the
subshell will list those individually, showing additional details:
Counting all files and directories in the current directory
Given the fact that commas (,) and periods (.) are hard links that mark the current and parent
directory, we need to count all entries minus these two
This can be done using the expr $(ls -a | wc -l ) - 2 command:
Here, the subshell will return the number of entries (five, in this case). The number we are looking for
is the number of entries minus the special folders ("." and ".."). In order to do arithmetic operations,
we use the expr command, as in our example.
Notice that the subshell contains a pipe. The good thing is that we can combine pipes and subshells in
any way in order to obtain the desired result.
Imagine pipes and subshells as Lego pieces for your shell. They expand way beyond its capabilities
and give you access to new possibilities with infinite combinations. In the end, it all depends on your