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BASH Shell Programming Basics
BASH is a type of UNIX shell which stands for Bourne Again SHell, named after it's author.
- UNIX is a free Operating System which as a basis to a Linux Distribution is becoming popular lately.
- A shell is the command line interface which allows for user input to control programs which operate various functions of the computer.
Why Would I want to program in BASH?
- BASH is available on most installations of Unix and Linux
- BASH is free to use
- BASH can be used to control and provide input and output of Linux Applications through the use of scripts
Basic Script Creation
- This guide assumes you are familiar with some aspects of text editors and Linux or UNIX. A text editor like Emacs, Vi, or Pico is used to create an ASCII text file.
- If not please read Using Vi
- Scripts which use BASH must have Linux execute permissions.
- The easiest way to make sure you have execute permissions is to create a blank text file using vi and then issuing the command chmod 700 myscript , with myscript being the name of the file you created.
After Initial Creation
Steps to make a BASH Script
- The BASH script needs the line #!/usr/bin/bash or its equivalent.
- If the path to BASH on your machine is different you can find it by using the command which bash
- You can use the number sign (#) to add a comment to make your program readable.
- Eg. #This is a comment, the program will not read this line
- Create a variable by directly assigning it
- mytext="hello world"
- Use echo or another built in command to create output
- echo displays on the screen what follows it.
- To use a variable, put the $ in front of it to use its value once it has already been assigned a value.
- echo "$mytext" will display "hello world" to the user
- echo "$mynumber is my favorite number" will display "27 is my favorite number"
- echo "mynumber" will display only "mynumber"
Your first "Hello World" BASH program
Using the above techniques you are now able to create your first BASH script.
- Putting together the examples above you have:
- #This is a comment
- mytext="hello world"
- echo "$mytext"
- Use ./program_name to execute the program
- Its output is "hello world"
- Mikkey, G (2000). BASH Programming - Introduction HOW-TO.