/bin/sh just points to
sh is supposed to run default command interpreter, which is
dash for Ubuntu.1
dash refers to Debian Almquist shell.
A shell is a command line interpreter for the system. There are several other shells like
zsh etc. Here is a brief excerpt from man page of
The shell is a command that reads lines from either a file or the termi‐
nal, interprets them, and generally executes other commands. It is the
program that is running when a user logs into the system (although a user
can select a different shell with the chsh(1) command). The shell imple‐
ments a language that has flow control constructs, a macro facility that
provides a variety of features in addition to data storage, along with
built in history and line editing capabilities. It incorporates many
features to aid interactive use and has the advantage that the interpre‐
tative language is common to both interactive and non-interactive use
(shell scripts). That is, commands can be typed directly to the running
shell or can be put into a file and the file can be executed directly by
There are lot of tutorials about Linux shells, you can start with this Wikipedia Article.
Coming to your question, if you write
file for you.