perl function no

The no keyword in Perl is used to turn off a particular module or pragma that was previously turned on using the use keyword. Here's an example:

use strict;
use warnings;

my $foo = 42;
print $foo;

no warnings 'once';
$bar = 99;
print $bar;

In this example, we turn on the strict and warnings pragmas using the use keyword. We then declare a variable $foo and print its value. Next, we use the no keyword to turn off the warnings pragma temporarily so that we can assign a value to an undeclared variable $bar. Finally, we print the value of $bar.

Without the no warnings 'once'; statement, Perl would display a warning message because we are assigning a value to an undeclared variable. By temporarily turning off the warnings pragma using the no keyword, we can suppress this warning.

Note that the no keyword only affects the current scope, so any modules or pragmas that were turned off using no will be turned back on when the scope ends.