perl function defined

The defined function in Perl is used to determine whether a variable has a defined value. Here's an example of how to use defined:

my $foo;
my $bar = 42;

if (defined $foo) {
  print "The value of \$foo is defined\n";
} else {
  print "The value of \$foo is undefined\n";
}

if (defined $bar) {
  print "The value of \$bar is defined\n";
} else {
  print "The value of \$bar is undefined\n";
}

In this example, two variables are declared: $foo and $bar. The defined function is used to check whether each variable has a defined value. In the first if statement, $foo has not been assigned a value, so defined returns false and the message "The value of $foo is undefined" is printed to the console. In the second if statement, $bar has been assigned the value 42, so defined returns true and the message "The value of $bar is defined" is printed to the console.

It's important to note that the defined function returns true if the value of the variable is anything other than undef, including the empty string, zero, and false. Therefore, it's useful for determining whether a variable has any kind of value, rather than just checking for a specific value.