my($ret) ||= foo();
What you're doing amounts to this, step-wise:
1. my ($ret); # Create a scalar variable called $ret
2. $ret ||= foo() # If $ret is undefined or zero, assign it to foo(
+)
But of COURSE $ret is undefined when you first declare it, because you haven't assigned it to anything!
A similarly bad thing is going on here:
my($ret) = $ret || foo();
where you're trying to create a new scalar variable my($ret), but its value depends on a previously defined scalar called $ret (notice that's the same variable name?), or foo() if the the value of the $ret was previously undefined or zero.
If you use strict and warnings (as you always should), then you'll get an error with the second one. Try this (essentially equivalent) code:
use strict;
use warnings;
my $x = $x || 5;
print "Now x = $x\n";
Without strict and warnings you get:
Now x = 5
but with them you get:
Global symbol "$x" requires explicit package name at test.pl line 5.
Execution of test.pl aborted due to compilation errors.
Finally, the reason your title is misleading (as diotalevi suggests), is because it's perfectly fine to do either:
use strict;
use warnings;
my $y = 7;
my $x;
$x = $x || $y;
print "Now x = $x\n";
and:
use strict;
use warnings;
my $y = 7;
my $x;
$x ||= $y;
print "Now x = $x\n";
which will both yield the expected:
Now x = 7
s''(q.S:$/9=(T1';s;(..)(..);$..=substr+crypt($1,$2),2,3;eg;print$..$/
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