This is fine:

if (open(my $fh, '<', $qfn)) {
    ...read from $fh...
}

# $fh is out of reach here
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Perl doesn't care where the my is to the point that it allows the following (even though the behaviour is officially undefined):

my $fh if ...;
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that's another thing:

if(my $x = expr) { ... } # my always executed
my $x if expr;           # my is conditional
if(expr) { my $x }       # as above
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what i was saying is that if i can my on a arg of a function, maybe i can do the same in the "argument" of a if

Oha

"as above" is unclear. I think you meant "my is conditional", but it's really "my always executed" (in the scope in which it resides).

c() or my $x;       # XXX Conditionally executed
c() and my $x;      # XXX Conditionally executed
my $x if c();       # XXX Conditionally executed (same as previous)
sub foo { my $x }   # OK  Always executed
if (c()) { my $x }  # OK  Always executed
die; my $x;         # OK  Always executed
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