Shell is an interface between the user and kernel. Shell takes the input from end user and converts is into a code understandable to the underlying kernel. Unix shells includes, sh, bash, Ksh, etc. The default shell in linux flavour is bash. Bash stands for Bourne Again SHell. The details of shell programming are as following:
Before proceeding towards programming, we must understand the capabilities of shell. Shell has a rich collection of variables as well as parameters. It has environment variables, positional parameters and special built in variables.
Shell special parameters are as following:
$$ : Contains process id of current shell.
$# : Contains the number of command line arguments.
$0 : Contains the name of the current shell / script.
$? : Contains the exit status of last executed command.
$* : Contains entire string of arguments.
$@ : Contains set of all arguments (we can say equivalent of $*)
$! : Contains process id of last background command.
Other than these shell has 9 positional parameters from $1 to $9. Environment variables includes HOME, IFS, PATH, PS1, PS2, PWD, and so on. To get the value of any of these parameters you can write echo $VARIABLENAME, as shown below:
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