Learning shell interpretation of commands

When we log in, the $ sign will be visible in the shell Terminal (# prompt if you are logged in as the root or administrator). The Bash shell runs scripts as the interpreter. Whenever we type a command, the Bash shell will read them as a series of words (tokens). Each word is separated by a space ( ), semicolon (;), or any other command delimiter. We terminate the command by pressing the Enter key. This will insert a newline character at the end of the command. The first word is taken as a command, then consecutive words are treated as options or parameters.

The shell processes the command line as follows:

• If applicable, the substitution of history commands
• Converting the command line into tokens and words
• Updating the history
• Processing quotes
• Defining functions and substitution of aliases
• Setting up of pipes, redirection, and background
• Substitution of variables (such as $name and $user) is performed
• Command substitution (echocal and echodate) is performed...