Putting the call inside a @{[ ... ]} construct does something different.

print "[@{ [ scalar test('abc') ] }]\n";
print "[", scalar test('abc'), "]\n\n";

print "[@{ [ test('abc') ] }]\n";
print "[", test('abc'), "]\n\n";

print "[@{ [ scalar test('123') ] }]\n";
print "[", scalar test('123'), "]\n\n";

print "[@{ [ test('123') ] }]\n";
print "[", test('123'), "]\n";

sub test
{
    my @rv = $_[0] =~ /^([0-9]+)$/;
    return @rv[ 0 .. $#rv ];
}
[download]

produces

[ ]
[[]

[]
[]

[123]
[123]

[123]
[123]
[download]

Running 5.8.4 on Solaris 9.

Cheers,

JohnGG