On May 15, Paul said:
>
>--- Peter Cornelius <[EMAIL PROTECTED]> wrote:
>> The <FILE> doesn't read into $_. You can add a 'print $_;' in there
>> to verify it. I think you're getting confused by the
>> while(<FILE>){...}
>> structure. This puts the result of the readline into $_ for you if
>> the <FILE> is the only thing in the '()'. Otherwise, I believe just
>> calling <FILE> on a line by itself sends that line to the bit bucket.
>
>I think that's right. On a line alone is a void context, but while(){}
>is a scalar context.
Perl changes certain things at compile-time. If you have a while loop
that can be optimized to 'while (<FH>)', then Perl turns that into 'while
(defined($_ = <FH>))' (and likewise for 'while ($x = <FH>)').
Watch and see:
friday:~ $ perl -MO=Deparse
while (<FH>) { 1 }
while ($x = <FH>) { 1 }
while (1 and <FH>) { 1 }
while (1 and $x = <FH>) { 1 }
while ($x and <FH>) { 1 }
while ($x and $y = <FH>) { 1 }
- syntax OK
while (defined($_ = <FH>)) {
'???';
}
while (defined($x = <FH>)) {
'???';
}
while (defined($_ = <FH>)) {
'???';
}
while (defined($x = <FH>)) {
'???';
}
while ($x and <FH>) {
'???';
}
while ($x and $y = <FH>) {
'???';
}
Those last two can't be optimized to a simple assignment from <FH>, so
Perl doesn't do its magical change.
--
Jeff "japhy" Pinyan [EMAIL PROTECTED] http://www.pobox.com/~japhy/
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Perl Programmer at RiskMetrics Group, Inc. http://www.riskmetrics.com/
Acacia Fraternity, Rensselaer Chapter. Brother #734
