Getting started
Hi all, I am Karthick from TechieDrone. Today I am going to share basic things that you should be aware to gain decent knowledge on shell scripting. Let’s dive in to the topic 😎 In this article, I am going to start with how to define variables in bash scripting and what are the methods to define variables with examples.
Constant variable through out the script
Simply declare a pre-defined variable globally like VariableName=YourVariableHere which will never change throughout the execution. For example, I am assigning A=1, B=2, C=$A. Here their value will be constant through out the execution. No matter how many times you run this script i.e., their value does not change 😀
Example:
1 2 3 | #!/bin/bash A=1;B=2;C=$A echo " a=$A \n b=$B \n c=$C" |
Result:
1 2 3 | a=1 b=2 c=1 |
Capture the output of something into a variable
In this method I am going to show how to assign a value of something into a variable with example. Say I am going to display formatted date as I need using bash script. Lets see how to achieve it. In this example, I’m going to show you two different workaround to capture the output of something into a variable. I will explain the difference between them in detail in later session 🙂
Example:
1 2 3 | #!/bin/bash customDate01=`date +%F`;customDate02=$(date +%D) echo " formatted date 01 : $customDate01 \n formatted date 02 : $customDate02" |
Result:
1 2 | formatted date 01 : 2018-03-03 formatted date 02 : 03/03/18 |
Assign run-time variable without prompt
It is nothing but getting the inputs for the variables in run-time. i.e., getting inputs at the run-time. Lets see how to do it 😉 Say I am going put below codes into a file named workaround-variables-eg3.sh. In this example I have assigned value for A & B during the execution (refer script execution part)
Example:
1 2 3 4 | #!/bin/bash A=$1;B=$2 C=`expr $A + $B` echo "Addition of $A and $B is $C" |
Script execution:
1 | sh workaround-variables-eg3.sh 1 3 |
Result:
1 | Addition of 1 and 3 is 4 |
Assign run-time variable with prompt
In above example, we assign variables in run-time without being prompt. i.e., We declared the value for A & B while executing the code. Here in this example, I am going to show how to get the inputs by displaying user friendly messages 💡 Say I am going put below codes into a file named workaround-variables-eg4.sh. In this example I have displayed some messages to get the input value for A & B during the execution (refer script execution part)
Example:
1 2 3 4 5 | #!/bin/bash read -p "Enter the value for A : " A read -p "Enter the value for B : " B C=`expr $A + $B` echo "Addition of $A and $B is $C" |
Script execution:
1 2 3 | sh workaround-variables-eg4.sh Enter the value for A : 2 Enter the value for B : 4 |
Result:
1 | Addition of 2 and 4 is 6 |
That’s all for now 😎 Still these concepts looks messy for you? No worries, feel free to ask us through comment section 🙂