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Perl if Statement

Summary : in this tutorial, you are going to learn about Perl if statement that allows you to control the execution of code conditionally.

Simple Perl if statement

Perl if statement allows you to control the execution of your code based on conditions. The simplest form of the if statement is as follows:

In this form, you can put the if statement after another statement. Let’s take a look at the following example:

The message is only displayed if the expression $a == 1 evaluates to true . How Perl defines true and false ? The following rules are applied when Perl evaluates an expression:

• Both number 0 and string “0” are false .
• The undefined value is false .
• The empty list () is false .
• The empty string "" is false .
• Everything else is true .

If you do not remember the rules or you doubt whether a condition is true or false , you can always write a simple if statement to test the expression.

The limitation of the Perl if statement is that it allows you to execute a single statement only. If you want to execute multiple statements based on a condition, you use the following form:

Noticed that the curly braces {} are required even if you have a single statement to execute. Watch out C/C++ and C# programmers!

The following flowchart illustrates the Perl if statement:

And the following is an example of using the if statement:

Perl if else statement

In some cases, you want to also execute another code block if the expression does not evaluate to true . Perl provides the if else statement that allows you to execute a code block if the expression evaluates to true , otherwise, the code block inside the else branch will execute.

The following flowchart illustrates the Perl if else  statement:

See the following example, the code block in the else branch will execute because $a and $b are not equal.

Perl if elsif statement

In some cases, you want to test more than one condition, for example:

• If $a and $b are equal, then do this.
• If $a is greater than $b then do that.
• Otherwise, do something else.

Perl provides the if elsif statement for checking multiple conditions and executing the corresponding code block as follows:

The following flowchart illustrates the if elseif else statement:

Technically speaking, you can have many elsif branches in an if elseif  statement. However, it is not a good practice to use a lengthy if elsif statement.

Perl if statement example

We are going to apply what we have learned so far to create a simple program called currency converter.

• We will use a hash to store the exchange rates.
• To get the inputs from users via the command line, we will use <STDIN>. We use the chomp() function to remove the newline character (\n) from the user’s inputs.
• We convert the amount from local currency to foreign currency if the currencies are supported.

The following source code illustrates the simple currency converter program:

In this tutorial, you’ve learned various forms of the Perl if statement including simple if , if else , and if esif else statements to control the execution of the code.

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The conditional (ternary) operator

Apr 16, 2013 by David Farrell

One way to reduce the verbosity of Perl code is to replace if-else statements with a conditional operator expression. The conditional operator (aka ternary operator) takes the form: logical test ? value if true : value if false .

Let’s convert a standard Perl if-else into its conditional operator equivalent, using a fictitious subroutine. First here is the if-else:

And here is the same statement using the conditional operator:

Hopefully this example shows how using the conditional operator can shorten and simplify Perl code. For further detail, check out the official documentation .

This article was originally posted on PerlTricks.com .

David Farrell

David is a professional programmer who regularly tweets and blogs about code and the art of programming.

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Unary, binary, ternary operators

The conditional operator, setting a limit.

Published on 2014-02-07

Author: Gabor Szabo

• about the translations

Conditional Decisions

Perl conditional statements allow conditions to be evaluated or tested with a statement or statements to be executed per the condition value which can be either true or false .

Perl does not have native boolean types. However, the numeric literal 0, the strings "0" and "", the empty array () and undef are all considered false in the context of condition evaluation.

Below are several types of conditional statements:

• if (condition) statement
• if (condition) {statement1; statement2; statement3;}
• if (condition) statement else statement
• if (condition) elsif (condition) statement else statement
• unless (condition) statement
• unless (condition) statement else statement
• unless (condition) elsif (condition) statement else statement

Ternary operator

The ? conditional operator is a simplified method of if (condition) statement else statement . It has the general form of: (condition) ? statement1 : statement2 .

First the condition is evaluated. If true, then statement1 is executed and becomes the value of the expression, otherwise, statement2 is executed and becomes the value of the expression.

Equality and Comparison Operators

These operators can be used to define conditions in conditional statements. Numeric values and string values are compared using different operators

Numeric values operators

• == true if the value of the left operand is equal to the value of right operand, else false
• != true if the value of the left operand is not equal to the value of right operand, else false
• ! negates the boolean value of whatever comes after this in a conditional expression
• <=> Compares the values of two numeric values and returns -1, 0, or 1 if the left argument is numerically less than, equal to, or greater than the right argument, respectively
• > true if the value of the left operand is smaller than the value of right operand, else false
• < true if the value of the left operand is lower than the value of right operand, else false
• >= true if the value of the left operand is smaller or equal than the value of right operand, else false
• <= true if the value of the left operand is lower or equal than the value of right operand, else false

String values operators

• eq true if the left argument is stringwise equal to the right argument
• ne true if the left argument is stringwise not equal to the right argument
• gt true if the left argument is stringwise greater than the right argument
• lt true if the left argument is stringwise less than the right argument
• ge true if the left argument is stringwise greater than or equal to the right argument
• le true if the left argument is stringwise less than or equal to the right argument
• cmp -1, 0, or 1 depending on whether the left argument is stringwise less than, equal to, or greater than the right argument, respectively

An array @family holds a list of family member names. The first hash %shoe_color contains favorite shoe color per person name. The second hash %shoe_size contains shoe size per person name.

Evaluate and print the favorite shoe color and shoe size per each family member. For shoe sizes 10 and above, add the word 'large' to the output line.

Output lines should be in the format: "Homer wears large brown shoes size 12".

Note : not all family members may be included in the hash variables, so you better conditionally check if they exist or not (using the exists operator). If a name does not exist, add the key/value pair into the hash variables - for show color add: black ; for shoe size add 99 .

Using if, elsif, else and unless

Perl if statements can consist of an 'if' evaluation or an 'unless' evaluation, an 'elsif' evaluation (yes the 'e' is missing), and an 'else' evaluation.

The syntax for an if statement can be arranged a few ways:

The unless statement is just like an 'if-not'. For example, the following two lines of code are equivalent:

Most commonly, you will see the following use of unless:

The else statement gets run when the preceding 'if' or 'unless' is not true:

If you want to check for more than one condition, you can build a larger statement using 'elsif':

The expression inside the 'if' condition, is evaluated. This means it is checked to see whether it is true or false. The following condition evaluates to true:

And the following evaluates to false:

The above example could also be written as:

You can also use if to check if a variable has a defined value. The following evaluates to false because $value has no defined value.

This works quite nicely with boolean values and objects, however you must be careful with strings. While the string in the following code has a defined value, it still evaluates to false:

This is because perl is not a strongly typed language. If you wanted to check if $value had a defined value, it is better to use the 'defined' function:

The c-style ? operator

Another way of writing an if statement is using the c-style shorthand conditional operator ?. This is very useful when assigning values. An example is:

If $flag evaluates to true, then $c will equal 4, otherwise $c will equal 5.

The form of 'if-else' statement can be easily embedded in other statements, for example, a print statement:

To find out more, run the command:

Perl if, else, elsif ("else if") syntax

Summary: This tutorial shows a collection of Perl if , else , and else if examples.

Here are some examples of the Perl if/else syntax, including the “else if” syntax, which is really elsif . (I wrote this because after working with many different languages I can never remember the “else if” syntax for most languages, and elsif is pretty rare.)

The Perl if/else syntax

The Perl if / else syntax is standard, I don’t have any problems here:

The Perl “else if” syntax (elsif)

The Perl “else if” syntax actually uses the elsif keyword. Here’s some example code that show this syntax:

Perl’s numeric and string comparison operators

While I’m in the neighborhood of Perl and equality/comparison tests, here’s a list of Perl’s numeric and string comparison/equality operators:

Not knowing the Perl has different operators for numeric tests and string tests can be a big “gotcha” when programming in Perl (so I wanted to make sure I noted this here).

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• Perl comparison operators
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• Introduction
• if and else
• while and until
• Regular expressions
• for and each
• Modules and packages
• Classes and objects
• Inheritance
• Using Moose

if and else in Perl

From here your real programming learning will start. In this chapter, you will learn about decision making. This means that if a user gives you some input, then you will learn to judge that input and then perform according to it.

In real life, we also make conditional decisions e.g.- If it is raining, then you will take an umbrella, else not; if it is your birthday, then it is a special day, else a normal day; if you want to allow some features in a website to the users with an account only, then you can think of - if user has an account, then this else not.

Now let's implement this in Perl.

In the first line, we are taking input. if ($a>10) - Here we used 'if' . First see $a>10 - The condition is comparing a with 10 and if a is greater than 10, then it is true and if smaller, then false . So, the whole story is that if a>10 ( if a is greater than 10 ), then print "your number is greater than 10\n"; will be executed, otherwise it will execute print "your number not greater than 10\n"; {} represents the bodies of 'if' and 'else'. This means that the statements written inside the curly braces '{}' after 'if' constitute the body of that 'if' and the statements inside the curly braces '{}' constitute the body of that 'else'. It will be clearer from examples. So, let's proceed for now.

See the flow diagram below.

We first write if (condition) ( where the condition is what has to be judged.. In the first example, the condition was ' a>10 ' ). The statements in the body of if will be executed only when this condition is true, otherwise the statements in the body of else will be executed. ( {} represents the bodies of 'if' and 'else').

Odd and even example

if ($a%2 == 0) : This is very simple to understand. $a%2 will give the remainder of the division of 'a' by 2. We know that if a number is divisible by 2, then it is even. So, if 'a' is divisible by 2, then 'a%2' will be 0. So, the whole story is that if a is divisible by 2 (a%2==0), then print "EVEN\n"; will be executed, otherwise print "ODD\n"; will be executed.

if under if

Yes, we can also use one if inside another. Let's see how to do this.

This is also called nesting. It is very simple. After giving input, firstly, the condition of the top-most 'if' will be checked i.e. ($a > 10000) . If it is true, then the statements inside this 'if' will be executed. The first statement inside this 'if' is if ($b eq "M") . So, this will be executed and if the condition of this if is also true, then the statements inside it will be executed, otherwise the statements inside the corresponding else will be executed.

Therefore, after giving the inputs of '12000' and 'F', the 'if' with condition 'a > 10000' became true. So, the statement in its body got executed. Now, the first statement inside it is another if with the condition b eq "M" which became false. So, the statement inside the corresponding 'else' got executed i.e. print "Your salary is good and you are a female\n"; .

Using elsif

elsif is used for else if. Imagine that there are 10 pockets of candies and each of them costs 1 coin. Now, if you have more than 10 coins, then you will buy 10. Else if you have 5 coins, then you will buy 5 pockets. Else you will buy less than 5 pockets. We do the same thing in Perl. Look at the following example to understand this.

I hope that you have already got this by just an example. Next lines will make it even clearer. The first condition in 'if' will be checked. If this condition is true, then only 'if' will be executed (i.e. its corresponding statements will be executed) and if it is false, then the compiler will check below. If the condition of 'if' is false, then the condition of 'elsif' will be checked. In the same way, if this condition is true, then its statements will be executed, otherwise the compiler will come below. If the conditions of 'if' and all 'elsif' are false, then only the statement corresponding to else(i.e. print "Enter valid input\n") will be executed.

We can have any number of 'elsif' after 'if'.

In the above example, we have given inputs of '8000' and 'M'. So, the condition of 'if' ( $a>10000 && b eq "M" ) is false since a is less than 10000. Now coming to the next 'elsif' having the condition ( $a>10000 && b eq "F" ), its condition is also false. The condition ( $a<=10000 && b eq "M" ) of the next 'elsif' is true because 8000 < 10000 and also 'b' is 'M'. So, the statement inside this 'elsif' got executed and ' Your salary is not so good and you are a male ' got printed on the screen.

Perl provides another tool for conditional flow and it is unless . It is exactly the opposite of 'if'. The statements inside 'if' are executed if the condition is true but the statements inside 'unless' are executed if the condition is false. Let's see an example to understand this.

We have entered 100 and it is less than 10000. So, the condition $>10000 is false and that's why the statement inside it got executed.

Another form of if else

We can also judge the condition using the ternary operator . Ternary operator checks whether a given condition is true and then evaluates the expressions accordingly. It works as follows.

condition ? expression1 : expression2;

If the condition is true , then expression1 gets evaluated, otherwise expression2 gets evaluated.

Here, if the condition ($age > 18) is true, then expression1 i.e. print("eligible to vote\n") will get evaluated, otherwise expression2 i.e. print("not eligible to vote\n") will get evaluated. Since the value of age that we entered (10) is less than 18, therefore the expression2 got evaluated and "not eligible to vote" got printed.

Let's see another example in which we want to find the greater among two numbers.

In this example, if the condition ($num2 > $num1) is true, then num2 i.e. 5 will get assigned to 'num', otherwise 'num1' i.e. 4 will get assigned to 'num'. In our case, the values of 'num1' and 'num2' are 4 and 5 respectively. Thus, the condition '$num2 > $num1' became and the value of num2 i.e. 5 got assigned to num and so 5 got printed.

my - Local variable

Suppose we have a variable having some value but we want to use a different value of the same variable only in one block of code. This can be easily done using a keyword my in Perl. Let's see an example to understand how it works.

Let's see one more example of using 'my' in 'if' block.

if-else Statement

Let's discuss if-else statements in detail, including nested-ifs with examples.

Branches in Perl

• The if-else statement
• Explanation
• Nested if-statements

We often need the execution of some portions of our code to be subject to a certain condition(s). Within the Perl programming language, the simplest and sometimes the most useful way of creating a condition within your program is through an if-else statement.

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Perl Else If

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• Introduction

Table of Contents

Understanding the Perl 'If' Statement

Introducing the perl 'else' statement, exploring the perl 'elsif' statement, common pitfalls and tips.

• The 'if' statement in Perl is used to execute a block of code if a certain condition is true. The syntax of the 'if' statement in Perl is as follows:
• The 'else' statement in Perl can be used in conjunction with the 'if' statement to execute a block of code if the condition in the 'if' statement is not true. Here is the syntax:
• Perl provides an 'elsif' keyword to allow for multiple, distinct conditions to be tested in sequence. The 'elsif' statement is only executed if the preceding 'if' or 'elsif' condition is not true and its own condition is true. The syntax is as follows:
• One of the most common pitfalls when using 'if-elsif-else' in Perl is the incorrect use of conditions. Always remember that the condition should return a boolean value (true or false).
• Another common mistake is forgetting to use the curly braces '{}' to define the scope of the 'if', 'elsif', and 'else' blocks. Without these, Perl will not know where the block begins and ends.
• It's crucial to remember that the conditions are evaluated from top to bottom. If a condition is true, Perl executes that block of code and skips the rest, even if they may also be true. Therefore, the order in which conditions are written is important.
• Lastly, 'elsif' in Perl is written as 'elsif', not 'elseif' or 'else if'. This is a common typo that can lead to syntax errors.

Perl if-else Statement

The if statement in Perl language is used to perform operation on the basis of condition. By using if-else statement, you can perform operation either condition is true or false. Perl supports various types of if statements:

The Perl single if statement is used to execute the code if condition is true. The syntax of if statement is given below:

Flowchart of if statement in Perl

Let's see a simple example of Perl language if statement.

Here, output is even number as we have given input as 10.

The Perl if-else statement is used to execute a code if condition is true or false. The syntax of if-else statement is given below:

Flowchart of if-else statement in Perl

Let's see the simple example of even and odd number using if-else statement in Perl language.

Here, input is an even number and hence output is even.

Perl If-else Example with Input from user

In this example, we'll take input from user by using standard input (<STDIN>/<>).

In the first output, user has entered number 5 which is odd. Hence the output is odd.

In the second output, user has entered number 4 which is even. Hence the output is even.

The Perl if else-if statement executes one code from multiple conditions. The syntax of if else-if statement is given below:

Flowchart of if else-if statement in Perl

The example of if else-if statement in Perl language is given below.

Perl - Assignment Operator

Learn Perl Assignment operator with code examples.

This tutorial explains about Perl assignment Operators

Perl assignments operators

Assignment operators perform expression and assign the result to a variable.

• Simple assignment
• Assignment Addition
• Assignment Subtraction
• Assignment Multiplication
• Assignment Division
• Assignment Modulus
• Assignment Exponent

Perl Assignment Operator

For example, We have operand1(op1)=6 and operand2(op2) =2 values.

Here is a Perl Assignment Operator Example

What Assignment operators are used in Perl scripts?

Arithmetic operators with assignments in Perl allow you to do arithmetic calculations on operands, and assign the result to a left operand. Addition(+=),Multiplication(*=),Subtraction(-=), Division(/=), Modulus(%=), Exponent(power (**=)) operators exists for this.

What are Assignment operators in Perl

there are 6 operators in Per for Assignment operators. Addition(+=),Multiplication(*=),Subtraction(-=), Division(/=), Modulus(%=), Exponent(power (**=)) operators exists for this.