Get to know Bash in under 4 minutes
Bash is a command language interpreter for interacting with a computer from the command line. It's
also called a shell because it surrounds the operating system kernel to hide its intricate details while
allowing you the programmer to do important stuff like access data and write files by typing simple
commands.
This was a revolutionary concept when it was developed in the early 70s back when programmers were
still using punch cards. The shell concept evolved over the years with the Bourne shell being the most
popular version that is until 1989 when the born-again shell or bash came about. When you open up the
terminal on a Unix machine like macOS and most Linux distros, the default shell is usually bash.It provides a prompt where you can type a command which will then be interpreted by the shell and
executed on the operating system. To find out if you';re running bash, type in which $ shell from the
command line. It's like any other application that lives in the binaries directory but bash is also a
programming language that allows us to write scripts.
This means anything we type manually into the command line can be automated with code. When you
first launch the shell, it actually runs a startup script that's defined in the bash profile or bashrc file on
your system. This allows you to customize the behavior and appearance of the shell whenever you start
a new session. You can add your own custom bash scripts to any project by creating a file that ends in .sh or no file extension at all. The first line in that file should always be a shebang followed by the path to the application that should run it. Below that, we can start writing commands like echo to print something and they'll be interpreted line by line.
To create a variable, type a name in all caps followed by the equal sign then reference it later in the
script using a dollar sign in front of the name. Now to execute the script, simply type the file name into
the shell. But what if we want to pass in some additional user input arguments when we run the script?
Positional arguments will automatically be assigned variable names of 1, 2, 3, and so on. In other cases, you may need additional user input in the middle of a script. You can create loops in bash
like a do while loop that will prompt the user to continue the script on a yes answer or exit on a no
answer. From there, we can implement conditional logic with an if statement which will test if the value
on the left side is less than the value on the right side. If true, then run this command; otherwise, run
the else command.
Another cool feature is that if you have multiple long-running processes, you can run them in parallel in
the background by adding an ampersand after the command. This has been bash, the born-again shell,
in under 4 minutes.
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