Bash if statement, if else statement, if elif else statement and nested if statement used to execute code based on a certain condition. There are numerous test conditions that you can use with if statements. The keyword “fi” indicates the end of the inner if statement and all if statement should end with the keyword “fi”. Sometimes, we want to process a specific set of statements if a condition is true, and another set of statements if it is false. Any code you want to run when an if condition is evaluated to false can be included in an else statement as follows: Now when you run the script as a regular user, you will be reminded that you are not the almighty root user: You can use an elif (else-if) statement whenever you want to test more than one expression (condition) at the same time. In the if/then/else form of the if statement, the block of statements after the then statement is executed if the condition succeeds. Also, note that the else block is optional. Basically, you just add semicolons after the commands and then add the next if-else statement. In this if-else-if ladder, the expressions are evaluated from top to bottom. When you just want to see the result in the shell itself, you may use the if else statements in a single line in bash. The following types of conditional statements can be used in bash. You can use all the if else statements in a single line like this: You can copy and paste the above in terminal and see the result for yourself. We can use if...else statement in Bash to run the statements if particular condition is satisfied or not. Run it and see it for yourself. In a conditional, you frequently have tasks to perform when the tested condition succeeds or fails. For example, the following age.sh bash script takes your age as an argument and will output a meaningful message that corresponds to your age: Now do a few runs of the age.sh script to test out with different ages: Notice that I have used the -lt (less than) test condition with the $AGE variable. #!/bin/bash # Checking the first argument provided if [[ -n $1 ]] then echo "You provided a value" else echo "You should provide something" fi Conclusion. If the temperature is greater than five, then the nested (inner) if-elif statement is evaluated. This way you can build much more efficient bash scripts and you can also implement error checking in your scripts. Bash way of writing Single and Multiline Comments, Salesforce Visualforce Interview Questions, Similar to Bash If statement, you may provide a single condition or multiple conditions after. In case one if the condition goes false then check another if conditions. These statements execute different blocks of code, depending upon whether a condition (or a boolean expression) provided by the programmer evaluates to true or false. También podemos usar el elif que nos permite comprobar si se cumplen varias condiciones. We also have the special elif on which we will see more in a minute. This tutorial describes how to compare strings in Bash. if..else Statement# Following is the form of Bash if..else statement: if TEST-COMMAND then STATEMENTS1 else STATEMENTS2 fi. In today’s tutorial, you learnt about the Bash “If Else” statement. From the bash variables tutorial, you know that $(command) syntax is used for command substitution and it gives you the output of the command. Now, let's create an example script root.sh. For example, if a user enters the marks 90 or more, we want to display “Excellent”. Any command of any length to be precise. Follow edited May 23 '17 at 10:30. Bash if-else statements are used to perform conditional tasks in the sequential flow of execution of statements. else echo "Number is odd." Don't believe me? To demonstrate, take a look at the following char.sh bash script: The script takes one character as an argument and displays whether the character is small/big alphabet, number, or a special character. Set of commands to be run when the is true. Output. I hope you have enjoyed making your bash scripts smarter! There must be space before and after the conditional operator (=, ==, <= etc). #Bash Script to check whether a number is even or odd read -p "Enter a number: " number if [ $((number%2)) -eq 0 ] then echo "Number is even." If the expression evaluates to true, statements of if block are executed. For example, input the marks of student and check if marks are greater or equal to 80 then print “Very Good”. If else is a conditional statement used in Bash scripting to execute different parts of your script based on the result of the if condition. If the result of TEST-COMMAND to True, it will execute the STATEMENTS1. Also be aware that you can have multiple elif statements but only one else statement in an if construct and it must be closed with a fi. if command then command executed successfully execute all commands up to else statement or to fi if there is no else statement else command failed so execute all commands up to fi fi Test conditions varies if you are working with numbers, strings, or files. Share. In Bash else-if, there can be multiple elif blocks with a boolean expression for each of them. That's the decent way of doing it but you are not obliged to it. This can be further enhanced to use if..elif..else and nested if so we will cover all such possible scenarios in this tutorial guide. 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