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Writing a Bash Shell Script

Bash shell scripts in Linux are text files that contain a series of commands that can be executed by the Bash shell. Bash (Bourne Again Shell) is a popular shell in Linux and UNIX systems, and shell scripts are used to automate tasks, configure systems, or perform a sequence of operations. How to Write a Bash Shell Script Create a New File: You can create a new script using any text editor like nano , vim , or gedit . gedit myscript.sh Write the Script: A basic shell script begins with a "shebang" ( #!/bin/bash ) to specify the interpreter that will be used to execute the script. The rest of the file contains the commands to be run. Example of a simple script: #!/bin/bash # This is a comment echo "Hello, World!" # Print "Hello, World!" #!/bin/bash : Specifies that the script will be executed using the Bash shell. echo "Hello, World!" : A command that prints the string "Hello, World!" to the terminal. Comments: Any line starting ...
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Different syntax for writing arithmetic expressions in bash shell

#!/bin/bash echo "Enter two numbers" read a b s=`expr $a + $b` echo "Sum1=$s" s=$[$a+$b] echo "sum2=$s" ((s=$a+$b)) echo "sum3=$s" ((s=a+b)) echo "sum3=$s" let s=$a+$b echo "sum4=$s" let s=a+b echo "sum4=$s" Note:bash shell support only integer arithmetic.zsh support operations on real numbers.We can use bc in bash shell to do real arithmetic. Eg: echo "$a*$b"|bc # where a and b are real Mathematical Operators With Integers Operator Description Example Evaluates To + Addition echo $(( 20 + 5 )) 25 - Subtraction echo $(( 20 - 5 )) 15 / Division echo $(( 20 / 5 )) 4 * Multiplication echo $(( 20 * 5 )) 100  % Modulus echo $(( 20 % 3 )) 2 ++ post-increment (add variable value by 1) x=5 echo $(( x++ )) echo $(( x++ )) 5 6 -- post-decrement (subtract variable value by 1) x=5 echo $(( x-- )) 4 ** Exponentiation x=2 y=3 echo $(( x ** y )) 8
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Flow Control in shell script - if and case statements

Shell script usually consist of sequence of commands that starts at the first line and continues line by line until it reaches the end. Most programs do much more than this. They make decisions and perform different actions depending on conditions. The shell provides several commands that we can use to control the flow of execution in our program. In this lesson, we will look at the following:  test if case exit   test The test command is used most often with the if command to perform true/false decisions. The command is unusual in that it has two different syntactic forms: # First form test expression # Second form [ expression ] The test command works simply. If the given expression is true, test exits with a status of zero; otherwise it exits with a status of 1. Common numerical test conditions -gt   Greater than -lt    Less than -ge  Greater than or equal to -le    Less than or equal to -eq   Equal to -ne...
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