[sf-perl] Odd behavior for dot operator?

david wright david_v_wright at yahoo.com
Fri Mar 18 09:10:03 PDT 2011

A handy module for this sort of thing is B::Deparse.

>From the docs:
With -p, it uses parentheses (almost) whenever they would be legal. 
This can be useful if you are used to LISP, or if you want to see how perl 
parses your input.

[dwright~(8)]$ perl -w -MO=Deparse,-p
$x = 'a' . (defined $y)? $y :'undef' ."\n";
print $x;
BEGIN { $^W = 1; }
($x = (('a' . defined($y)) ? $y : "undef\n"));
- syntax OK

From: Andrew Sigmund <ASIGMUND at altera.com>
To: Francisco Obispo <fobispo at isc.org>
Cc: "SanFrancisco-pm at pm.org" <SanFrancisco-pm at pm.org>
Sent: Thu, March 17, 2011 11:19:01 PM
Subject: Re: [sf-perl] Odd behavior for dot operator?

Yup, that was the problem.  I verified that the precedence of the dot operator 
is higher than that of the conditional operator.
So, by default, I was getting
$x = ( 'a' . (defined $y) )? $y ....  which is always true, so perl was trying 
to actually use the undefined $y, and thus gave me the warning.

Thanks Francisco.


-----Original Message-----
From: Francisco Obispo [mailto:fobispo at isc.org]
Sent: Thursday, March 17, 2011 23:03
To: Andrew Sigmund
Cc: SanFrancisco-pm at pm.org
Subject: Re: [sf-perl] Odd behavior for dot operator?

the problem is the precedence or the operators.


$x = 'a' . ( (defined $y) ? $y :'undef' ."\n");  # now I try to put something up 
print $x;

On Mar 17, 2011, at 10:55 PM, Andrew Sigmund wrote:

> $x = 'a' . (defined $y)? $y :'undef' ."\n";  # now I try to put something up 
> print $x;

Francisco Obispo
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email: fobispo at isc.org
Phone: +1 650 423 1374 || INOC-DBA *3557* NOC
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