How can I selectively access elements returned by a Perl subroutine?

Pull off the first argument only via list context:

my ( $wanted ) = array_returning_sub( @args );

TIMTOWTDI with a slice:

my $wanted = ( array_returning_sub( @args ) )[0];

---

Both styles could be extended to extract the n'th element of the returned array, although the list slice is a bit easier on the eye:

my ( undef, undef, $wanted, undef, $needed ) = array_returning_sub( @args );

my ( $wanted, $needed ) = ( array_returning_sub( @args ) )[2,4];

Slices

use warnings;
use strict;

sub foo {
    return 'a' .. 'z'
}

my $y = (foo())[3];
print "$y\n";

__END__

d

Alternately, you do not need an intermediate variable:

use warnings;
use strict;

sub foo {
    return 'a' .. 'z'
}

print( (foo())[7], "\n" );

if ( (foo())[7] eq 'h') {
    print "I got an h\n";
}

__END__

h
I got an h

One way could be [(arrayoutput(some argument))]->[0].