What is a variable in shell scripting ?
A variable is a character string to which we assign a value. The value assigned could be a number, text, filename, device, or any other type of data.
A variable is nothing more than a pointer to the actual data. The shell enables you to create, assign, and delete variables.
Variable Names:
The name of a variable can contain only letters (a to z or A to Z), numbers ( 0 to 9) or the underscore character ( _).
The following examples are valid variable names
_MJIT
VAR_1
VAR_2
Following are the examples of invalid variable names −
2_VAR
-VARIABLE
VAR1-VAR2
VAR_A!
The reason you cannot use other characters such as !, *, or - is that these characters have a special meaning for the shell.
Become Master In Ansible Click here
Defining Variables
Variables are defined as follows
variable name=variable_value
NAME="mjit"
To access the value stored in a variable, prefix its name with the dollar sign ($)
#!/bin/bash
NAME=” WELCOME TO MAHO JASE INSTUTITE OF TECHNOLOGY”
echo$ NAME
output:
learn python click here
Assingning a variable value to another variable
#!/bin/bash
value1=20
value2=value$1
echo " The resulting value is $value2
Output:
Types of Variable Types:
Three Types of varibles
Local Variables − A local variable is a variable that is present within the current instance of the shell. It is not available to programs that are started by the shell. They are set at the command prompt.
Environment Variables − An environment variable is available to any child process of the shell. Some programs need environment variables in order to function correctly. Usually, a shell script defines only those environment variables that are needed by the programs that it runs.
Shell Variables − A shell variable is a special variable that is set by the shell and is required by the shell in order to function correctly. Some of these variables are environment variables whereas others are local variables.
Use of Backtick symbol (`) in shell variables:
The backtick allows you to assign the output of a shell command to a variable. While this doesn’t seem like much, it is a major building block in script programming. You must surround the entire command line command with backtick characters:
DAY=`date'
#!/bin/bash
DAY=`date
value2=value$1
echo " Today date and time is $DAY"
Become Devops Engineer click here
