Since the Bourne Again SHell is a superset of sh, all sh commands will also work in bash – but not vice versa. bash has many more features of its own, and, as the table below demonstrates, many features incorporated from other shells.
Bash common features
The following features are standard in every shell. Note that the stop, suspend, jobs, bg and fg commands are only available on systems that support job control.
Bash catching signals
Your system contains a man page listing all the available signals, but depending on your operating system, it might be opened in a different way.
Shell functions are a way to group commands for later execution, using a single name for this group, or routine. The name of the routine must be unique within the shell or script. All the commands that make up a function are executed like regular commands.
Bash advanced variables
There are cases when you want to avoid this kind of behavior, for instance when handling telephone and other numbers. Apart from integers and variables, you may also want to specify a variable that is a constant. This is often done at the beginning of a script, when the value of the constant is declared.
Bash select menu and shift
The select construct allows easy menu generation.
Bash repetitive tasks ( for , while , until )
To run a specific task or list of commands repetitively on bash script , you need to use on of this three constructions : for , while , until . Each one fits different situation as we will know now.
Bash interactive scripts
Some scripts run without any interaction from the user at all. Advantages of non-interactive scripts include: The script runs in a predictable way every time. The script can run in the background.
Bash conditional if and case statements
At times you need to specify different courses of action to be taken in a shell script, depending on the success or failure of a command. The if construction allows you to specify such conditions.
How to use awk
AWK is another popular stream editor, just similar to SED. The basic function of awk is to search files for lines or other text units containing one or more patterns. When a line matches one of the patterns, special actions are performed on that line.