Linux scripting if guide

Master the If Statement in Shell Scripting on Linux: A Comprehensive Guide

Learn the syntax, usage, and advanced features of if statements in Bash on Linux. Automate tasks and increase control with efficient and effective shell scripts using conditional statements. Master the If statement in shell scripting now!

• Syntax of If Statements
• Adding Else and Elif Statements
• Bash if statement
• Combining Multiple Conditions with the && Operator
• Comparison Operators in If Statements
• Advanced Usage of If Statements
• Other code examples for the shell if statement in Bash on Linux
• Conclusion
• How do I use the IF command in Bash?
• How do you write if in Bash?
• How do you do if statements in shell?
• What is == in shell?

If statements are essential in shell scripting as they allow you to test a condition and execute specific statements based on the result. In this guide, we will cover the syntax, usage, and advanced features of if statements in Bash on Linux. By the end of this guide, you will have a thorough understanding of how to use if statements in shell scripts.

Syntax of If Statements

The syntax of an if statement includes the if keyword, the conditional phrase, and the then keyword, and ends with the fi keyword.

if [ $num1 -gt $num2 ] then echo "num1 is greater than num2" fi 

The above code is an example of how to use the if statement in Bash. Here, the condition is [ $num1 -gt $num2 ] , which means if num1 is greater than num2 , then the statement inside the if block will be executed.

Adding Else and Elif Statements

An else statement can be added to the if statement to execute specific statements when the condition is false. The elif statement can be used to add additional conditions to the if statement.

if [ $num1 -gt $num2 ] then echo "num1 is greater than num2" elif [ $num1 -eq $num2 ] then echo "num1 is equal to num2" else echo "num1 is less than num2" fi 

The above code is an example of how to use if-else and if-elif-else structures. Here, the condition checks if num1 is greater than num2 . If that is true, then the first statement is executed. If the first condition is false, the elif statement checks if num1 is equal to num2 . If that is true, then the second statement is executed, and if both conditions are false, the else statement is executed.

Bash if statement

Bash Scripting on Linux (The Complete Guide) Class 05 — If Statements · Git and GitHub for Duration: 13:31

Combining Multiple Conditions with the && Operator

The && operator can be used to combine multiple conditions in the if statement, all of which must be true for the statements to execute.

if [ $num1 -gt $num2 ] && [ $num1 -gt $num3 ] then echo "num1 is the greatest" fi 

The above code is an example of how to use the && operator in an if statement. Here, the condition checks if num1 is greater than both num2 and num3 . If that is true, then the statement inside the if block will be executed.

Comparison Operators in If Statements

The == operator is used to compare two operands for equality, and the != operator is used to compare two operands for inequality.

if [ $name == "John" ] then echo "Hello John!" fi 

The above code is an example of how to use the == operator in an if statement. Here, the condition checks if the value of the name variable is equal to “John”. If that is true, then the statement inside the if block will be executed.

Advanced Usage of If Statements

The if statement can be used to check the success or failure of a command and execute specific statements based on the result.

if grep -q "example" file.txt then echo "example found in file.txt" else echo "example not found in file.txt" fi 

The above code is an example of how to use if statements to check the success or failure of a command. Here, the grep command is used to search for the word “example” in the file.txt . If the word is found, then the statement inside the if block is executed, and if not, then the statement inside the else block is executed.

Other code examples for the shell if statement in Bash on Linux

In Shell , for instance, bash if statement

and - && or - ||# and example if [ -r $1 ] && [ -s $1 ] then echo This file is useful. fi# or example if [ $USER == 'bob' ] || [ $USER == 'andy' ] then ls -alh else ls fi

In Shell , for example, bash if code sample

#!/bin/bashfoo="qux" bar="qux"if [ "$foo" = "$bar" ]; then echo "The strings are equal." else echo "The strings aren't equal." fi

In Shell as proof, bash else if code example

if [ "$animal" == "penguin" ]; then echo "Hmmmmmm fish. Tux happy!" elif [ "$animal" == "dolphin" ]; then echo "Pweetpeettreetppeterdepweet!" else echo "*prrrrrrrt*" fiif TEST-COMMANDS; then CONSEQUENT-COMMANDS; elif MORE-TEST-COMMANDS; then MORE-CONSEQUENT-COMMANDS; else ALTERNATE-CONSEQUENT-COMMANDS; fi

In Shell , for instance, if statement in shell script code example

 if [ "$result" == "1" ] then echo "test" >> /home/samurai/test.txt fi if [[ "$result" -eq "1" ]] then echo "test" >> /home/samurai/test.txt fi 

In Shell , for instance, bash if else code sample

# Basic syntax if [[ condition_1 ]]; then echo "Code to execute if condition_1 is true" elif [[ condition_2 ]]; then echo "Code to execute if condition_1 is false and condition_2 is true" else echo "Code to execute if condition_1 and condition_2 are false" fi# Note, the syntax for the one-line equivalent is: if [[ condition_1 ]]; then echo "Code to execute if condition_1 is true"; elif [[ condition_2 ]]; then echo "Code to execute if condition_1 is false and condition_2 is true"; else echo "Code to execute if condition_1 and condition_2 are false"; fi# Note to self, see this link for more on bash operators and [ ] vs [[ ]]: # https://tldp.org/LDP/abs/html/comparison-ops.html

In Shell case in point, if and if bash code example

In Shell case in point, bash if statement code sample

Operator Description ! EXPRESSION The EXPRESSION is false. -n STRING The length of STRING is greater than zero. -z STRING The lengh of STRING is zero (ie it is empty). STRING1 = STRING2 STRING1 is equal to STRING2 STRING1 != STRING2 STRING1 is not equal to STRING2 INTEGER1 -eq INTEGER2 INTEGER1 is numerically equal to INTEGER2 INTEGER1 -gt INTEGER2 INTEGER1 is numerically greater than INTEGER2 INTEGER1 -lt INTEGER2 INTEGER1 is numerically less than INTEGER2 -d FILE FILE exists and is a directory. -e FILE FILE exists. -r FILE FILE exists and the read permission is granted. -s FILE FILE exists and it's size is greater than zero (ie. it is not empty). -w FILE FILE exists and the write permission is granted. -x FILE FILE exists and the execute permission is granted. 

In Shell , in particular, if else bash shell script

if [[ some condition ]]; then do_this elif [[ another condition ]]; then do_that_a elif [[ yet another condition]]; then do_that_b else do_that_default_thing fi 

In Shell , for example, bash if code sample

nome=tiago ## with SPACE between variable and comparation if [ $nome == 'tiago' ] ; then echo "hello Tiago" fi

In Shell as proof, bash ifelse code sample

# you can use it if you want but it isn't very accurate # as of best practices and such for DB in $( sudo mysql -e 'show databases' -s --skip-column-names ) ; do if [ $DB == 'information_schema' ] || [ $DB == 'performance_schema' ]; then echo 'warning' ; else echo "success $DB"; fi done 

Conclusion

If statements are essential in shell scripting, and mastering them can help you automate tasks and increase control and flexibility in program flow. By understanding the syntax, usage, and advanced features of if statements, you can create efficient and effective shell scripts on Linux.

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