Question

How can I Initialise and clear multiple hash in one line.

Ex:

my %hash1 = ();
my %hash2 = ();
my %hash3 = ();
my %hash4 = ();

to

my ( %hash1, %hash2, %hash3, %hash4 ) = ?

Answer 1

It appears (from your comments) that you really want to empty hashes that already have stuff in them. You can do it like this:

(%hash1,%hash2,%hash3) = ();

Complete example:

use strict;
use warnings;

my %hash1 = ('foo' => 1);
my %hash2 = ('bar' => 1);
my %hash3 = ('baz' => 1);

(%hash1,%hash2,%hash3) = ();

print (%hash1,%hash2,%hash3);

A variable declaration always gives you an empty variable, so there is no need to set it to empty. This is true even in a loop:

for (0..100)
{
    my $x;
    $x++;
    print $x;
}

This will print 1 over and over; even though you might expect $x to retain its value, it does not.

Explanation: Perl allows list assignment like ($foo,$bar) = (1,2). If the list on the right is shorter, any remaining elements get assigned undef. Thus assigning the empty list to a list of variables makes them all undefined.

Another useful way to set a bunch of things is the x operator:

my ($x,$y,$z) = (100)x3;

This sets all three variables to 100. It doesn’t work so well for hashes, though, because each one needs a list assigned to it.