Bash Else If
Bash Else If statements are an important part of Bash scripting. They allow for complex conditional actions to be executed based on a variety of situations. Understanding how to use Bash Else If statements is crucial for productive Bash scripting. In this article, we will explore the basics of Bash Else If and its different forms, including if, if..else, if..elif..else, and nested if statements. We will also explain test operators and logical operators such as OR and AND, with examples provided throughout the tutorial. By the end of this article, you will have a solid understanding of Bash Else If and be able to use it in your own Bash scripting projects.
Basic Bash If
The Bash If statement is the most basic form of conditional statement in Bash scripting. It allows a program to make decisions based on different conditions. According to Linux Hint, the Bash If statement checks whether a certain condition is true or false and then executes the code block that follows, depending on the result. Here, we will explore the basics of the Bash If statement, including its syntax and an example of it in use.
Syntax of Bash If Statement
The syntax of the Bash If statement is as follows:
if [ condition ]
then
# code block to execute if condition is true
fi
The keyword if is followed by a space and then the condition to be evaluated, enclosed within square brackets. The then keyword is used to start the code block that will execute if the condition is true. The code block is ended by the fi keyword.
Example of Bash If Statement
Here is an example of how to use the Bash If statement in a Bash script, as provided by Linux Hint. The script checks whether a file named example.txt exists in the current directory. If it does exist, it prints a message to the console.
#!/bin/bash
if [ -e example.txt ]
then
echo "The file example.txt exists."
fi
In this example, the -e flag is used to check whether the file exists. If it does exist, the echo command is executed, printing the message to the console.
Bash If Else
The Bash If Else statement is an extension of the Bash If statement. If the condition in the If statement is false, the program can execute a different code block using the Else statement. In this section, we will explore the Bash If Else statement, including its syntax and an example of it in use.
Syntax of Bash If Else Statement
The syntax of the Bash If Else statement is as follows:
if [ condition ]
then
# code block to execute if condition is true
else
# code block to execute if condition is false
fi
The if statement checks the condition and executes the code block following then if the condition is true. If the condition is false, the code block following else is executed. The fi keyword denotes the end of the If statement.
Example of Bash If Else Statement
Here is an example of how to use the Bash If Else statement in a Bash script, as provided by Linuxize. The script checks if a number is smaller than 10. If it is, it prints a message to the console saying that the number is smaller than 10. If it is not, it prints a message saying that the number is greater than or equal to 10.
#!/bin/bash
number=5
if [ $number -lt 10 ]
then
echo "$number is smaller than 10."
else
echo "$number is greater than or equal to 10."
fi
In this example, the -lt flag is used to check if the number is less than 10. If it is, the first message is printed to the console. If not, the second message is printed.
Bash If Elif Else
The Bash If Elif Else statement is a further extension of the Bash If statement and Bash If Else statement. It allows for multiple conditions to be evaluated, and different code blocks to be executed based on the result. In this section, we will explore the Bash If Elif Else statement, including its syntax and an example of it in use.
Syntax of Bash If Elif Else Statement
The syntax of the Bash If Elif Else statement is as follows:
if [ condition1 ]
then
# code block to execute if condition1 is true
elif [ condition2 ]
then
# code block to execute if condition1 is false and condition2 is true
else
# code block to execute if all conditions are false
fi
The if statement checks the first condition and executes the code block following then if the condition is true. If the condition is false, the elif statement checks the second condition. If the second condition is true, the code block following then is executed. If both conditions are false, the else statement is executed, and the code block following then is executed. The fi keyword denotes the end of the If statement.
Example of Bash If Elif Else Statement
Here is an example of how to use the Bash If Elif Else statement in a Bash script, as provided by GeeksforGeeks. The script checks if a number is positive, negative, or zero. If it is positive, it prints a message saying that the number is positive. If it is negative, it prints a message saying that the number is negative. If it is zero, it prints a message saying that the number is zero.
#!/bin/bash
number=-10
if [ $number -gt 0 ]
then
echo "$number is positive."
elif [ $number -lt 0 ]
then
echo "$number is negative."
else
echo "$number is zero."
fi
In this example, the -gt flag is used to check if the number is greater than zero. The -lt flag is used to check if the number is less than zero. If neither condition is met, the final message is printed.
Bash Nested If
The Bash Nested If statement is a form of the Bash If statement that allows one or more If statements to be nested within another If statement. This allows for complex conditional statements to be created, with multiple levels of conditions. In this section, we will explore the Bash Nested If statement, including its syntax and an example of it in use.
Syntax of Bash Nested If Statement
The syntax of the Bash Nested If statement is as follows:
if [ condition1 ]
then
# code block to execute if condition1 is true
if [ condition2 ]
then
# code block to execute if condition1 and condition2 are true
fi
fi
The if statement checks the first condition and executes the code block following then if the condition is true. If the condition is false, the nested if statement checks the second condition. If both conditions are true, the code block following then in the nested if statement is executed.
Example of Bash Nested If Statement
Here is an example of how to use the Bash Nested If statement in a Bash script, as provided by JavaTpoint. The script checks if a number is positive, negative, or zero. If it is positive, it prints a message saying that the number is positive. If it is negative, it prints a message saying that the number is negative. If it is zero, it prints a message saying that the number is zero. If the number is greater than 100, it prints a message saying that the number is greater than 100.
#!/bin/bash
number=120
if [ $number -gt 0 ]
then
echo "$number is positive."
if [ $number -gt 100 ]
then
echo "$number is greater than 100."
fi
elif [ $number -lt 0 ]
then
echo "$number is negative."
else
echo "$number is zero."
fi
In this example, the -gt flag is used to check if the number is greater than zero. If it is, the nested if statement checks if the number is greater than 100. If both conditions are true, the two messages are printed to the console.
Bash If Else If
The Bash If Else If statement is a form of the Bash If statement that allows for multiple conditions to be evaluated and different code blocks to be executed based on the results. It is commonly used when dealing with a range of values or conditions. In this section, we will explore the Bash If Else If statement, including its syntax and an example of it in use.
Syntax of Bash If Else If Statement
The syntax of the Bash If Else If statement is as follows:
if [ condition1 ]
then
# code block to execute if condition1 is true
elif [ condition2 ]
then
# code block to execute if condition1 is false and condition2 is true
elif [ condition3 ]
then
# code block to execute if condition1 and condition2 are false and condition3 is true
else
# code block to execute if all conditions are false
fi
The if statement checks the first condition and executes the code block following then if the condition is true. If the condition is false, the elif statement checks the second condition. If the second condition is true, the code block following then is executed. If both conditions are false, the next elif statement is checked, and so on. If all conditions are false, the else statement is executed, and the code block following then is executed. The fi keyword denotes the end of the If statement.
Example of Bash If Else If Statement
Here is an example of how to use the Bash If Else If statement in a Bash script, as provided by LinuxHint. The script checks if a number is positive, negative, or zero. If it is positive, it prints a message saying that the number is positive. If it is negative, it prints a message saying that the number is negative. If it is zero, it prints a message saying that the number is zero.
#!/bin/bash
number=0
if [ $number -gt 0 ]
then
echo "$number is positive."
elif [ $number -lt 0 ]
then
echo "$number is negative."
else
echo "$number is zero."
fi
In this example, the -gt flag is used to check if the number is greater than zero. If it is, the first message is printed to the console. If not, the -lt flag is used to check if the number is less than zero. If it is, the second message is printed. If neither condition is met, the final message is printed.
Bash If Statement with Logical Operators
The Bash If statement can be used in combination with logical operators to create more complex conditional statements. Logical operators allow you to test multiple conditions at once, and determine whether all or some of them are true. In this section, we will explore the Bash If statement with logical operators, including its syntax and an example of it in use.
Syntax of Bash If Statement with Logical Operators
The syntax of the Bash If statement with logical operators is as follows:
if [ condition1 ] && [ condition2 ]
then
# code block to execute if both condition1 and condition2 are true
fi
if [ condition1 ] || [ condition2 ]
then
# code block to execute if either condition1 or condition2 is true
fi
The && operator is used to test if both conditions are true. If both conditions are true, the code block following then is executed. The || operator is used to test if either of the conditions is true. If either condition is true, the code block following then is executed.
Example of Bash If Statement with Logical Operators
Here is an example of how to use the Bash If statement with logical operators in a Bash script, as provided by Linuxize. The script checks if a user is logged in and has sudo privileges. If the user is logged in and has sudo privileges, it prints a message saying that the user is logged in and has sudo privileges. If not, it prints a message saying that the user does not have the required privileges.
#!/bin/bash
if [ $(id -u) != 0 ]; then
echo "This script must be run as root."
exit 1
fi
if [[ $(sudo -n uptime 2>&1) = *"load"* ]]; then
echo "User is logged in and has sudo privileges."
else
echo "User does not have the required privileges."
fi
In this example, the first if statement checks if the user is logged in as root. If not, it prints an error message and exits the script. The second if statement uses the sudo command to test if the user has sudo privileges. If the command returns output containing the word “load”, the user is considered to be logged in and have sudo privileges. The appropriate message is then printed to the console.
Bash If Statement with Test Operators
The Bash If statement can also be used in combination with test operators to check for specific conditions. Test operators are used to test for file attributes, string comparisons, and numeric comparisons. In this section, we will explore the Bash If statement with test operators, including its syntax and examples of it in use.
Syntax of Bash If Statement with Test Operators
The syntax of the Bash If statement with test operators is as follows:
Numeric comparisons
if [ num1 -eq num2 ]
then
# code block to execute if num1 is equal to num2
fi
if [ num1 -ne num2 ]
then
# code block to execute if num1 is not equal to num2
fi
if [ num1 -lt num2 ]
then
# code block to execute if num1 is less than num2
fi
if [ num1 -le num2 ]
then
# code block to execute if num1 is less than or equal to num2
fi
if [ num1 -gt num2 ]
then
# code block to execute if num1 is greater than num2
fi
if [ num1 -ge num2 ]
then
# code block to execute if num1 is greater than or equal to num2
fi
String comparisons
if [ str1 = str2 ]
then
# code block to execute if str1 is equal to str2
fi
if [ str1 != str2 ]
then
# code block to execute if str1 is not equal to str2
fi
if [ -z str ]
then
# code block to execute if str is empty
fi
if [ -n str ]
then
# code block to execute if str is not empty
fi
File attribute checks
if [ -e file ]
then
# code block to execute if file exists
fi
if [ -f file ]
then
# code block to execute if file is a regular file
fi
if [ -d file ]
then
# code block to execute if file is a directory
fi
if [ -r file ]
then
# code block to execute if file is readable
fi
if [ -w file ]
then
# code block to execute if file is writable
fi
if [ -x file ]
then
# code block to execute if file is executable
fi
Examples of Bash If Statement with Test Operators
Here are some examples of how to use the Bash If statement with test operators in a Bash script, as provided by GeeksforGeeks.
Numeric comparisons
#!/bin/bash
num1=2
num2=3
if [ $num1 -eq $num2 ]; then
echo "$num1 is equal to $num2"
elif [ $num1 -lt $num2 ]; then
echo "$num1 is less than $num2"
else
echo "$num1 is greater than $num2"
fi
String comparisons
#!/bin/bash
str1="hello"
str2="world"
if [ $str1 = $str2 ]; then
echo "Strings are equal"
else
echo "Strings are not equal"
fi
File attribute checks
#!/bin/bash
file="/etc/passwd"
if [ -e $file ]; then
echo "File exists"
else
echo "File does not exist"
fi
Wrapping Up
In this article, we have explored the Bash If statement, including its syntax and examples of it in use with various types of conditional statements. We have also looked at how to use logical and test operators with the Bash If statement to create more complex conditional statements.
Bash scripting is a powerful tool that can be used to automate a wide range of tasks on Linux systems. By mastering the Bash If statement and its various forms, you can create powerful scripts that can save you time and effort.
We hope that this article has been helpful in providing you with a better understanding of the Bash If statement and its many uses. If you have any questions or comments, please feel free to leave them below.
And don’t forget to check out our other great content on Linux Home Page for more tips and tricks on Linux and open-source software.
Questions and Answers
What is the Bash Else If statement?
Bash Else If is a conditional statement used to test multiple conditions in a Bash script.
How does the Bash Else If statement work?
The Bash Else If statement works by testing a series of conditions in sequence until one is found to be true.
Who uses the Bash Else If statement?
The Bash Else If statement is used by Linux system administrators and developers who work with Bash scripts.
What are some examples of Bash Else If in use?
Bash Else If can be used to check if a file exists, if a user is logged in, or if a command has executed successfully.
How do I use Bash Else If in my Bash script?
To use Bash Else If in your Bash script, you can use the syntax if condition1; then ... elif condition2; then ... else ... fi.
What if my Bash Else If statement has too many conditions?
If your Bash Else If statement has too many conditions, you can use logical operators to combine them into a single test.