if ( my $t = shift ) { 
   $t =~ s/change_something/to_something_else/;
} 
print "$t\n";   # out of scope here
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Somewhat surprisingly then, this does not work:

print $t if (my $t = shift);
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doom's explanation is wrong. It has nothing to do with order. Even if you fixed the order, it still wouldn't work.

(my $t = shift) and print $t;   # Fails.
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Variables cannot be used (by name) in the statement in which they are declared. This allows statements such as my $t = $t; to work.

print $t if (my $t = shift);       # Fails.
my $t = shift; print $t if $t;     # Ok.
if (my $t = shift) { print $t; }   # Ok.
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if behaves similar to for in this respect.

Yes good point. I always forget about that, too... sometimes you'd like to have the loop counter defined after the loop is over, but you have to make a special effort to do that. This won't work, for example:

my @list = qw( wuhn tew thuree foah DONE whateva you know);
for my $i (0..10) {
  last if ($list[$i] eq 'DONE');
}
print "final index: $i\n";
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Somewhat surprisingly then, this does not work:

print $t if (my $t = shift);
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Well, I wouldn't say that that's exactly a surprise -- after all, it's a fairly odd thing to do, declaring it's a lexical after you use it... This doesn't work either:

$t = shift;
print $t;
my $t;
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