GrandFather showed you how to pass the array. However, it would be more efficient if a reference to the array was passed:

&rien2rien(\@ut);

.
.
.

sub rien2rien
{
    my $other = shift;
    for (my $i = 0; $i < @$other; $i++)
    {
        my $a = $other->[$i]{'first'};
        my $b = $other->[$i]{'second'};
        print "in other sub:\t$a\t$b\n";
    }
}
[download]

Other problems:

1) $a and $b have special meanings for sort. Using them as normal variables can cause unexpected problems. Use other names instead.

2) You're using prototypes (e.g. sub rien2rien(@)), which is a bad idea.

3) You use the ampersand notation for calling functions (e.g. &rien2rien(@ut) ) which overrides the prototype, also a bad idea.

4) You're using a C-style for loop, which is much less readable and no more efficient than a Perl-style for loop, or even a foreach loop:

sub rien2rien
{
    my $other = shift;
    foreach (@$other)
    {
        my $var1 = $_->{'first'};
        my $var2 = $_->{'second'};
        print "in other sub:\t$var1\t$var2\n";
    }
}
[download]