[Melbourne-pm] Simple(?) question involving backticks and die

Tim Connors tconnors+pmmelb at astro.swin.edu.au
Wed Jan 4 21:38:28 PST 2006

On Thu, 5 Jan 2006, Benji Wakely wrote:

> On Thu, 5 Jan 2006 16:27:29 +1100 (EST), 
> Tim Connors <tconnors+pmmelb at astro.swin.edu.au> wrote:
> >>   my @list = `/bin/ls /home` || die ("Couldn't list files");
> >
> >Aren't you meant to use "or" rather than "||" when using die, for 
> >precedence reasons?  Could this be what is happening? `` becomes scalar 
> >context when combined with the ||  ?
> That checks out, and now I'll happily use 'or' rather than '||' 
> in this situation.
> ...Wish I knew why it was so, though.


Because what you were trying to do was to || the backticks with the die, 
and then assigning the result into the array.  || forces the backticks to 
become a scalar, and the result is true, so die doesn't evaluate to 
anything.  Hence, the scalar ends up in the first element of the array.

The alternatives, are to bracket things correctly, forcing the evaluation 
of the backticks in array context, then assigning that to the array, and 
then evaluating whether to die.  Or use "or", which has a lower precedence 
than "||", as it is meant to be used -- the proper idiom is to use:

$blah=blah() or die()
rather than
$blah=blah() || die()

Read up on precedence in a perl or C book somewhere.

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