Perl/Basics/Boolean Logic/Statements

Perl > Basics > Boolean Logic > Statements

if

An if statement may have 3 types of clauses: if,elsif, and else. For the below example, assume that the $age scalar is passed as a command line argument:

if (int($age) == $age) { #Making sure it's an integer. if ($age < 18) { #If the age is less than 18: print "You must be at least 18 to view this.\n"; } elsif ($age < 21) { # If the age is more than 18, but less than 21: print "Because you are under 21, some features may be restricted.\n"; } else { # If none of the conditions have been met: display_content(); } }

unless

An unless statement may only have the unless clause and an else clause.

unless ($age >= 21) { print "All content is restricted for users under the age of 21.\n"; } else { print "Welcome to our sample age gate!\n"; display_content(); }

AND and OR

"And" and "or" are used to apply multiple conditions to a boolean statement.

• && is the way perl represents "and"
• || is the way perl represents "or"

Example:

if ($age < 21 && $age >= 18) { print "Some content will be restricted because you are not older than 21.\n"; }

switch

To use perl's switch() routine you must have use Switch; before your switch() statement. A switch statement allows a programmer to avoid long chains of "elsif" statements. It condenses the amount of required lines of code. Perl's switch statement is very similar to the switch() statement in C and C++, though the syntax is a little different. A perl switch() statement may contain case and else clauses. Perl switch cases can also be used to determine if a value is in a list, an array element, hash key, or matches a regular expression or string. In this example, suppose $option was a numeric value for an integer based menu with 3 options.

use Switch; switch(int($option)) { case 1 { # Essentially the same as if ($option == 1) print "You picked option 1!\n"; } case 2 { # Essentially the same as elsif ($option == 2) print "You picked option 2!\n"; } case 3 { # Essentially the same as elsif ($option == 3) print "You picked option 3!\n"; } else { print "invalid menu option!\n"; } }

For more information, see perldoc switch, or: here.

Golfing

The term golfing applies to condensing a boolean statement into one line. Golfing is typically used when you only need to execute one line of code for a boolean statement.

print "You are not 18 or older!\n" unless ($age >= 18);

• Is essentially the same as:

print "You are not 18 or older!\n" if ($age < 18);

• Is essentially the same as this un-golfed statement:

unless ($age >= 18) { print "You are not 18 or older!\n"; }