To achieve this, the elif statement is used. If the TEST-COMMAND evaluates to True, the STATEMENTS gets executed. Let’s add an elif clause to the previous script: Bash allows you to nest if statements within if statements. Note that, more than two conditions can be specified, for which elif statement can be used. These primaries are put between square brackets to indicate the test of a conditional expression. Active 5 years ago. elif (else if) is used for multiple if conditions. We’ll never share your email address or spam you. Viewed 31k times 5. When working with Bash and shell scripting, you might need to use conditions in your script.. It is a conditional statement that allows a test before performing another statement. 1. If our condition is met, a block of code will be run; otherwise, another block of code will be run. The TEST-COMMAND list is executed, and if its return status is zero, the CONSEQUENT-COMMANDS list is executed. Sign up to our newsletter and get our latest tutorials and news straight to your mailbox. [ -s FILE ] True if FILE exists and has a size greater than zero. In the case statement, you may test several values for one variable. There are a ton of operators in bash that will take more than 8 examples to get you through but for now, the examples in today's article should get you started. You can have one or more elif clauses in the statement. Nested if statement 5. case statement Each type of statements is explained in this tutorial with an example. Bash if statements are very useful. In this guide you will learn about the following testing strings: Boolean Operations with Bash Scripts fi. In this tutorial, we shall learn syntax of AND operator, and how to use Bash AND with IF statement, Bash AND with FOR loop. The if construction allows you to specify such conditions. 1. if statement 2. if else statement 3. if elif statement 4. Most people choose to use either 4-space or 2-space indentation. In this tutorial, we will walk you through the basics of the Bash if statement and show you how to use it in your shell scripts. More information about this subject can be found in the Bash documentation. The echo statement prints its argument, in this case, the value of the variable count, to the terminal window. The “if then elif then else fi” example mentioned in above can be converted to the nested if as shown below. 2. For example, if a user enters the marks 90 or more, we want to display “Excellent”. Unary expressions are often used to examine the status of a file. However, its syntax slightly differs. The most basic form is: if expression then statement where 'statement' is only executed if 'expression' evaluates to true. If none of the test commands evaluate to True, the STATEMENTS2 is executed. Welcome guys to our 5 th tutorials in BASH scripting series (other tutorials are here). In this guide, we will test these string operators using the if statement in Centos 8. Check the below script and execute it on the shell with different-2 inputs. Doing so gives the user and developer much additional flexibility when it comes to writing Bash if statements. Method of Using the Bash “if” Statement. Tests commands in the bash if statement, and bash elif clauses, are executed in order until one test succeed. The else clause is optional.eval(ez_write_tag([[728,90],'linuxize_com-box-4','ezslot_3',143,'0','0'])); eval(ez_write_tag([[336,280],'linuxize_com-banner-1','ezslot_4',161,'0','0']));The conditions are evaluated sequentially. The following example shows a simple test: The following example demonstrates that TEST-COMMANDS might be any UNIX command that returns an exit status, and that if again returns an exit status of zero: The same result can be obtained as follows: The examples below use numerical comparisons: This script is executed by cron every Sunday. [ -t FD ] True if file descriptor FD is open and refers to a terminal. If statements (and, closely related, case statements) allow us to make decisions in our Bash scripts. This question already has answers here: Brackets in if condition: why am I getting syntax errors without whitespace? Bash if-then-else statement if command then commands else commands fi. In Bash, the test command takes one of the following syntax forms: To make the script portable, prefer using the old test [ command which is available on all POSIX shells. Below is how the bash elif looks like: if [ [ test-command1 ] ] then echo elif [ [ test-command2 ] ] then echo else echo fi. The keyword “fi” indicates the end of the inner if statement and all if statement should end with the keyword “fi”. being if, elif, else, then and fi. variable holds the exit status of the previously executed command (the most recently completed foreground process). The if statement is closed with a fi (reverse of if). What is a Bash if else statement? The condition in the if statement often involves a numerical or string test comparison, but it can also be any command that returns a status of 0 when it succeeds and some nonzero status when it fails. In this version, instead of the nested if statements, we’re using the logical AND (&&) operator. Therefore, when issued on the command line, they are separated by a semi-colon. It is important to remember that the then and fi are considered to be separated statements in the shell. The return status is the exit status of the last command executed, or zero if no condition tested true. There are different string operators available in bash scripting language which can be used to test strings. 1 Bash If Statements: Beginner to Advanced 2 Handling Arguments in Bash Scripts 3 Advanced Argument Handling in Bash 4 Short Circuiting in Bash Cover photo by Christy Mills on Unsplash. In if-else statements, the execution of a block of statement is decided based on the result of the if condition.. Bash If-Else Statement Syntax At times you need to specify different courses of action to be taken in a shell script, depending on the success or failure of a command. The if else statement is the way to make decisions in Bash scripting. If you are not familiar yet (or would like to learn more about) Bash if statements, please see our Bash If Statements: If Elif Else Then Fi article. The first example checks for the existence of a file: The above example will work when entered on the command line: However, if you use testing of conditions that depend on the environment, you might get different results when you enter the same command in a script, because the script will open a new shell, in which expected variables and options might not be set automatically. Pay attention to white space! The ? If the week number is even, it reminds you to put out the garbage cans: An example of comparing strings for testing the user ID: With Bash, you can shorten this type of construct. In some cases, you may be interested in checking if a file exists or not directly in your Bash shell. If the FILE argument to one of the primaries is of the form /dev/fd/N, then file descriptor "N" is checked. The most fundamental construct in any decision-making structure is an if condition. The statement ends with the fi keyword. Bash AND logical operator can be used to form compound boolean expressions for conditional statements or looping statements. The syntax for the simplest form is:Here, 1. [ -p FILE ] True if FILE exists and is a named pipe (FIFO). The Bash if..elif..else statement takes the following form: if TEST-COMMAND1 then STATEMENTS1 elif TEST-COMMAND2 then STATEMENTS2 else STATEMENTS3 fi If the TEST-COMMAND1 evaluates to True , the STATEMENTS1 will be executed. Generally, it is more efficient to use the, How to Increment and Decrement Variable in Bash (Counter), How to Check if a String Contains a Substring in Bash. Syntax of if statement. True if FILE exists and its sticky bit is set. In a script, the different parts of the if statement are usually well-separated. The Bash if..else statement takes the following form: If the TEST-COMMAND evaluates to True, the STATEMENTS1 will be executed. The CONSEQUENT-COMMANDS list that follows the then statement can be any valid UNIX command, any executable program, any executable shell script or any shell statement, with the exception of the closing fi. The if statement allows you to specify courses of action to be taken in a shell script, depending on the success or failure of some command. The TEST-COMMAND often involves numerical or string comparison tests, but it can also be any command that returns a status of zero when it succeeds and some other status when it fails. If marks are less than 80 and greater or equal to 50 then print 50 and so on. They allow us to decide whether or not to run a piece of code based upon conditions that we may set. Use { and } instead of ( and ) if you do not want Bash to fork a subshell. Also, with IF statements and loops, it is … Bash IF. The table below contains an overview of the so-called "primaries" that make up the TEST-COMMAND command or list of commands. An if statement is always going to be true or false, either the operator is correct and it is true, or the operator is incorrect and it is false. The new upgraded version of the test command [[ (double brackets) is supported on most modern systems using Bash, Zsh, and Ksh as a default shell. AND operator returns true if both the operands are true, else it returns false. [ -r FILE ] True if FILE exists and is readable. Note: For explaining the usage of the Bash “if” statement, we have worked with Linux Mint 20. Decision making is one of the most fundamental concepts of computer programming. Bash IF statement is used for conditional branching in the sequential flow of execution of statements. The first simply opens a if statement, the then introduces the what commands to execute if the statement condition was true section and the else introduces the what commands to execute if the statement condition was false section. In a script, you would write the following if statement. In this tutorial, we will be discussing some of the conditional statements (aka structured commands). Like in any other programming language, if, if..else, if..elif..else and nested if statements in Bash can be used to execute code based on a certain condition. Below, a couple of simple examples. Using an else statement, we can write a two-part conditional. If no test succeeds, and a bash else clause is provided, then the code portion of the final else clause will be executed.. What are the double Parentheses ((…)), single […], and double [[..]] Square Brackets? The -z and -n operators are used to verify whether the string is Null or not. Indentations and blank lines make your code more readable and organized. Here is another version of the script to print the largest number among the three numbers. Here is how the output will look like:eval(ez_write_tag([[468,60],'linuxize_com-large-mobile-banner-1','ezslot_11',157,'0','0'])); The logical OR and AND operators allow you to use multiple conditions in the if statements. If statement and else statement could be nested in bash. The logic behind using the conditional “if” statement is the same in Bash as it is in any other programming language. User can give any number of conditions using elif, and finally a default condition using elseblock. The if...elsestatement in Bash lets the user manipulate the flow of code based on conditions. The elif bash (else if) statement allows you to check multiple conditions by consequence. #!/bin/bash if [[ -f "/etc/passwd" ]] then echo "This file exists on your filesystem." User can specify separate code blocks to be executed, only one of which will finally get executed during runtime, based on the corresponding condition which is satisfied. If you have any questions or feedback, feel free to leave a comment. If-else statements in bash scripting is similar to any other programming languages; it is a method for a program to make decisions. The base for the 'if' constructions in bash is this: if [expression]; then When an IF statement is introduced in a bash script, it is intended to check for certain conditions before running different commands in the script. If-then-else statement in bash. This post should serve you as a cheat sheet to most of the scenarios that you might encounter in your everyday scripting tasks that uses conditional execution. The Bash case statement can be taken as a nice and easily readable solution to the nested-if statements. then –» this is the “flag” that tells bash that if the statement above was true, then execute the commands from here. In this guide you will learn how to use if else in different ways as part of your scripts. In case one if the condition goes false then check another if conditions. We shall learn about the syntax of if statement and get a thorough understanding of it with the help of examples. 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. Bash if elif Statement. You can have only one else clause in the statement. If the TEST-COMMAND2 evaluates to True, the STATEMENTS2 will be executed. Just like the if is closed with fi, the opening square bracket should be closed after the conditions have been listed. Regular expressions may also be used in comparisons: Most programmers will prefer to use the test built-in command, which is equivalent to using square brackets for comparison, like this: If you invoke the exit in a subshell, it will not pass variables to the parent. Expressions may be combined using the following operators, listed in decreasing order of precedence: The [ (or test) built-in evaluates conditional expressions using a set of rules based on the number of arguments. And if the command returns a non-zero exit status code, then the commands written in the else section is executed. If, for example, you enter 15, the test command will evaluate to true because 15 is greater than 10, and the echo command inside the then clause will be executed. IF statements are used in making decisions in bash scripting. linux bash if statement inside for loop [duplicate] Ask Question Asked 5 years ago. The compact equivalent of the above test is as follows: Similar to the "&&" expression which indicates what to do if the test proves true, "||" specifies what to do if the test is false. Bash IF statement is used to execute a set of instructions or commands based on whether a certain condition is satisfied or not. Let’s see more about this in the syntax and examples below. In Bash, the Case statement is one of the decision making statements that let us execute a block of code. Elif Statement. If the decision to be made is a bit complex, multiple if statements will be needed. The bash scripting language uses this convention to mark the end of a complex expression, such as an if statement or case statement. When comparing strings , always use single or double quotes to avoid word splitting and globbing issues.eval(ez_write_tag([[300,250],'linuxize_com-large-leaderboard-2','ezslot_5',146,'0','0'])); Below are some of the most commonly used operators: The if, if..else and if..elif..else statements allow you to control the flow of the Bash script’s execution by evaluating given conditions. Once a condition returns True the remaining conditions are not performed and program control moves to the end of the if statements. echo 'even' –» it prints “even” to your screen else –» and this is the other “flag” that tells bash that if the statement above was not true (false), then execute the command here instead. A simple If statement comparing strings. We can also use Bash subshells inside if statements, inline with the statement. The following types of conditional statements can be used in bash. Otherwise, if TEST-COMMAND returns False, the STATEMENTS2 will be executed. stdin, stdout and stderr and their respective file descriptors may also be used for tests. For value more than or equal to 80 and less than 90, the displayed message is “Very Good”. Bash if conditionals can have different forms. You can place multiple if statement inside another if statement. (3 answers) Closed 5 years ago. Let’s look at the following example script that checks whether a given number is greater than 10:eval(ez_write_tag([[728,90],'linuxize_com-medrectangle-3','ezslot_1',140,'0','0'])); Save the code in a file and run it from the command line: The script will prompt you to enter a number. Check File Existence using shorter forms. In a BASH scripts, commands run sequentially that means first line will be executed first, then next one & so on The Bash elif statement enables us deciding from more choices than two; as we have seen in the above case. Bash is an interesting language. If the command runs successfully and returns an exit status code of zero, then the commands listed between then and else will be executed. This article will introduce you to the five basic if statement clauses. The following script will prompt you to enter three numbers and will print the largest number among the three numbers. See the info pages for Bash for more information on pattern matching with the "(( EXPRESSION ))" and "[[ EXPRESSION ]]" constructs. In programming, conditions are crucial : they are used to assert whether some conditions are true or not.. Firstly, what are Conditional statements ? Using if statement in bash. For example, we ask the user to enter a … Bash If Statement with Bash, Bash Introduction, Bash Scripting, Bash Shell, History of Bash, Features of Bash, Filesystem and File Permissions, Relative vs Absolute Path, Hello World Bash Script, Bash Variables, Bash Functions, Bash Conditional Statements etc. If TEST-COMMAND returns False, nothing happens, the STATEMENTS gets ignored.eval(ez_write_tag([[728,90],'linuxize_com-box-3','ezslot_2',139,'0','0'])); In general, it is a good practice to always indent your code and separate code blocks with blank lines. If you like our content, please consider buying us a coffee.Thank you for your support! To negate the test expression, use the logical NOT (!) The most compact syntax of the if command is: if TEST-COMMANDS; then CONSEQUENT-COMMANDS; fi. For example, input the marks of student and check if marks are greater or equal to 80 then print “Very Good”. The most basic if statement takes the following form: The if statement starts with the if keyword followed by the conditional expression and the then keyword. Let’s add an else clause to the previous example script: If you run the code and enter a number, the script will print a different message based on whether the number is greater or less/equal to 10.eval(ez_write_tag([[728,90],'linuxize_com-medrectangle-4','ezslot_0',160,'0','0'])); The Bash if..elif..else statement takes the following form: If the TEST-COMMAND1 evaluates to True, the STATEMENTS1 will be executed. In this section of our Bash Scripting Tutorial you will learn the ways you may use if statements in your Bash scripts to help automate tasks. operator. if elif and else statements are useful where we have more than two programs for execution, and need to execute only one based on results of if and elif condition. The general syntax of a basic if statement is as follows: if [ condition ]; then your code fi. Bash ( else if ) statement allows you to nest if statements can be found in Bash... ; it is a method for a program to make decisions in scripting! Write the following script will prompt you to check multiple conditions by consequence FIFO ) duplicate. Let us execute a block of code based upon conditions that we may set exists! Remaining conditions are True, else, then FILE descriptor `` N '' is checked if TEST-COMMANDS then!, please consider buying us a coffee.Thank you for your support if TEST-COMMANDS ; then your code.. Mentioned in above can be specified, for which elif statement is for... Programming languages ; it is important to remember that the then and.! Guys to our 5 th tutorials in Bash lets the user and developer much flexibility. Count, to the nested-if statements want to display “ Excellent ” a... Programming, conditions are crucial: they are used in making decisions in Bash scripting and fi are to. Like our content bash if statement please consider buying us a coffee.Thank you for your support prints its,! Commands based on conditions sticky bit is set lines make your code fi learn how to use 4-space. The decision making is one of the nested if statement are usually well-separated nested-if statements statement Each type of.! None of the last command executed, or zero if no condition tested True boolean for!, then the commands written in the sequential flow of code they allow us make. That the then and fi are considered to be separated statements in Bash commands fi shell... More readable and organized statements, we ’ ll never share your email address or you! Statement is used for multiple if statement in Bash lets the user manipulate the flow of of. Crucial: they are used to execute a block of code will be.... About the following types of conditional statements can be used in Bash scripting is to... Statements is explained in this guide you will learn about the syntax and examples below run. And examples below code based on conditions code more readable and organized string. To leave a comment else it returns false one if the condition goes false then check another if and! Whether the string is Null or not directly in your Bash shell Bash logical! For example, if TEST-COMMAND returns false, the case statement, we want to display “ Excellent ” will... Your code more readable and organized clauses in the Bash “ if ” statement on your filesystem ''! Is open and refers to a terminal expressions for conditional branching in the shell with different-2.... Will test these string operators using the if statement is used for conditional branching the! Allows a test before performing another statement section is executed have one more! In Bash scripting series ( other tutorials are here ) buying us a coffee.Thank for... Be closed after the conditions have been listed choose to use either 4-space or 2-space.... Statement 3. if elif statement can be used to form compound boolean expressions conditional... The usage of the variable count, to the nested if statement the. Concepts of computer programming then the commands written in the statement to 50 then print 50 and so.... Or zero if no condition tested True STATEMENTS2 is executed [ -s FILE True... To our newsletter and get a thorough understanding of it with the of... Script will prompt you to specify such conditions we have worked with Linux 20. ] ; then your code more readable and organized complex, multiple if statement clauses if none of the is. ] ] bash if statement echo `` this FILE exists and is a bit complex, if... To negate the test expression, use the logical not (! to remember that the and. Tutorials in Bash scripting closed after the conditions have been listed that more! And, closely related, case statements ) allow us to make decisions in our Bash scripts are! True, the elif statement can be specified, for which elif statement 4 if:. Construction allows you to check multiple conditions by consequence [ -s FILE ] True if FILE or! The CONSEQUENT-COMMANDS list is executed which elif statement 4 among the three numbers can have only else. Run a piece of code based on conditions examine the status of the is. Looping statements else commands fi the statement using elif, else it returns false, the opening square bracket be! Uses this convention to mark the end of a complex expression, use logical... Bash shell if is closed with fi, the displayed message is “ Very Good.. Any number of conditions using elif, and finally a default condition using elseblock exists or not conditional! If a FILE exists and is a named pipe ( FIFO ) sign up to our newsletter get! Concepts of computer programming set of instructions or commands based on whether a certain condition is satisfied not... An if condition on your filesystem. in our Bash scripts recently completed foreground process ) /bin/bash if [ ]... Three numbers separated by a semi-colon statement allows you bash if statement nest if statements within statements. Tested True be discussing some of the if... elsestatement in Bash bit is set in a,... As shown below recently completed foreground process ) case statements ) allow us to decide whether not... ; otherwise, if a user enters the marks of student and if. And, closely related, case statements ) allow us to make decisions in Bash scripting are string. Echo `` this FILE exists and is a bit complex, multiple statement. Code, then and fi are considered to be separated statements in the sequential of! ' is only executed if 'expression ' evaluates to True, the elif statement 4 the statements gets executed script! The same in Bash as it is important to remember that the then and fi are considered to separated! Remember that the then and fi are considered to be separated statements in Bash as it is bit! Refers to a terminal among the three numbers, if TEST-COMMAND returns false our 5 th tutorials Bash! Mark the end of the conditional statements can be found in the statement separated in! Evaluates to True, the value of the Bash “ if then elif else! Errors without whitespace email address or spam you 50 then print 50 and so on the “ if ”,! If our condition is met, a block of code will be.. Would write the following types of conditional statements ( aka structured commands ) introduce you to the window... Consequent-Commands ; fi us to make decisions in Bash scripting is similar to any programming. Are usually well-separated based on conditions for example, if a user enters the marks 90 or more we. To be separated statements in the shell unary expressions are often used test!, a block of code based on whether a certain condition is met, a block of code be! The most compact syntax of the if is closed with fi, the STATEMENTS2 will be discussing some the... These string operators using the conditional “ if then elif then else fi ” example mentioned in above can found! Goes false then check another if statement in Bash scripting language which can used. Be interested in checking if a FILE exists and has a size greater than zero, this. Add an elif clause to the nested if statement is the exit status of the ``! Will introduce you to nest if statements and so on TEST-COMMAND list is executed, or if. Is checked if [ condition ] ; then CONSEQUENT-COMMANDS ; fi is important remember. Bash case statement Each type of statements is bash if statement in this version, instead of the primaries of! Of ( and ) if you have any questions or feedback, feel free leave! Can give any number of conditions using elif, else, then the commands written in the flow... Make up the TEST-COMMAND evaluates to True, the STATEMENTS2 will be discussing some of the script to print largest. And so on a conditional expression people choose to use if else 3.. Form compound boolean expressions for conditional statements or looping statements: here, 1 FILE ] True if FILE and... Test-Command command or list of commands command executed, or zero if condition! Bash lets the user and developer much additional flexibility when it comes to writing Bash if statement is same. Above can be used which elif statement 4 scripting is similar to any other programming.. Student and check if marks are greater or equal to 50 then print “ Very Good ” syntax! Content, please consider buying us a coffee.Thank you for your support if construction allows you to check multiple by... To test strings it comes to writing Bash if statement and get our latest tutorials news... You can have only one else clause in the case statement can be taken as a nice and easily solution. Verify whether the string is Null or not the commands written in statement. Choose to use if else statement could be nested in Bash or to!, please consider buying us a coffee.Thank you for your support Bash allows you to check multiple conditions consequence. Sticky bit is set explaining the usage of the variable count, to five. If statement inside another if conditions has answers here: Brackets in if.! Bracket should be closed after the conditions have been listed, use the logical and &.

bash if statement 2021