February 25, 2010 — I used to use Python, Ruby or even PHP to write backend programs that would automate things like server management tasks, development and editing tasks, deployment tasks, backup tasks, and so forth.
Then I learned what is basically the BASH programming language, a language very similar to Python/Ruby/PHP etc., but is perfect for writing command line programs.
Here's the core of what you need to know:
A BASH script should have the .sh extension, just as a Python script has the .py extension, a php script has the .php extension, and a Ruby script has the .rb extension.
#!/bin/bash
Here's your first bash script (name it hello.sh):
#!/bin/bash<br>
echo "Hello World"
The echo command prints a string and also a new line at the end.
Your script must be *executable*. To make it executable, you need to change the file permissions. This would make your hello.sh script executable:
chmod 777 hello.sh
To run your script, from the directory where your script is located, type this:
./hello.sh
The "./" substitutes the current directory. In other words, typing
./hello.sh
Is equivalent to typing the full path to the file such as this:
/home/breck/hello.sh
Command line parameters are accessed with $1, $2, etc. Create a new script called hello2.sh. Put this in it:
#!/bin/bash
echo "Hello World"
echo $1
echo $2
Now run your script like this:
./hello2.sh hi breck
It should print this:
Hello World
hi
breck
The hi got stored in $1, and the breck got stored in $2.
Functions are pretty simple and straightforward:
#!/bin/bash
echo "Hello World"
echo $1
echo $2
function hi_name {
echo "hi"
echo $1
}
hi_name $3
Notice you don't need parenthesis and other junk. Name this file hello3.sh and run it with this:
./hello2.sh hi breck conor
It should print this:
Hello World
hi
breck
hi
conor
Notice what's going on with parameter passing and scope.
That's it for now. As you can see, BASH is a very clean, simple, yet powerful programming language. Get started with it slowly and gradually build up your skills with it.