Re: Trying to read a filehandle inside a loop

The diagnostics error is due to the fact that the reading of a file could return 0 which would evaluate to false in a boolean context, whereas you want to be testing for definedness. The reason you can't read from <DATA> within the loop is that you've already slurped it in the foreach. So in this case a while loop would make a lot more sense e.g

use strict;
use diagnostics;

my $line = (<DATA>);
print "line ouside loop = $line";

while(my $line = <DATA>) {

    print "line from foreach = $line";

    $line = (<DATA>) or print "error reading filehandle\n";
    $line ||= "null\n";
    print "line inside loop = $line";

}

__DATA__
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[download]

HTH

_________ broquaint

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Re: Re: Trying to read a filehandle inside a loop by roik (Scribe) on Oct 23, 2002 at 09:31 UTC
Thanks for your explanation. I can see now that the foreach has 'slurped' the data from the filehandle, so there is no data to read inside the loop. Why doesn't the 'while' loop slurp the data too? I'll have a look in perlsyn I think! Cheers.	[reply]
Re: Re: Re: Trying to read a filehandle inside a loop by broquaint (Abbot) on Oct 23, 2002 at 09:42 UTC
Why doesn't the 'while' loop slurp the data too? Because the filehandle is only evaulated in a scalar context, so you'll only get one line per iteration. Whereas a `foreach` loop evaluates the filehandle in a list context which produces the list which it iterates over. Another thing to be aware of is that if you're iterating over a filehandle in a `while` loop perl will auto-magically stick a `defined` test around your condition e.g `while(my $line = <DATA>) # becomes while (defined(my $line = <DATA>))` [download] So now if a single 0 is read the loop will continue. HTH `_________ broquaint`	[reply] [d/l]