Setting aside why you want to do this, how about: 

#!/usr/bin/env perl
use strict;
sub f {
        return 2;
}

sub g {
        my ($y) = shift @_;
        return $y*2;
}

if ( my $k = g(my $x = f())  ) {
        print "If the answer is four I'm happy.  Answer == $k\n";
}

[download]
That example seems to do all that you want.
update: Test platform was perl v5.8.6


Be Appropriate && Follow Your Curiosity

In reply to Re: scope of my $x in if statements by mikeraz
in thread scope of my $x in if statements by perl5ever

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