Re: What exactly does "$| = 1;" do?

[Jan Eden]

Hi Todd,

Todd W wrote on 16.12.2004:

>
>"Robert" <[EMAIL PROTECTED]> wrote in message
>news:[EMAIL PROTECTED]
>> I have seen in a few scripts now, including some of the articles that Mr.
>> Schwartz has written. I have read it does something with the buffers but
>on
>> a more technical level what is that?
>>
>> Robert
>>
>
>Along with the other explinations, consider an example:
>
>[EMAIL PROTECTED] trwww]$ perl
>use warnings;
>use strict;
>
>foreach my $i ( 1 .. 5 ) {
>  print($i, '...');
>  sleep( 1 );
>}
>print( "\n" );
>
>$| = 1;
>sleep( 1 );
>
>foreach my $i ( 1 .. 5 ) {
>  print($i, '...');
>  sleep( 1 );
>}
>print( "\n" );
>^D
>1...2...3...4...5...
>1...2...3...4...5...
>
>The first line is all printed out at once. The second line prints
>'1...' then waits a second then prints '2...' and so on.
>

That's what I knew about $|, too. But with the following script, it does not 
work as expected:

___BEGIN CODE___

#!/usr/bin/perl -wT

use CGI;
use strict;
use LWP::UserAgent;

my $q = new CGI;

print $q->header(-type=>'text/html', -charset=>'utf-8'),
        $q->start_html("URL-Checker"),
        $q->h1('URL-Checker');
        
if ($q->param) {
    my $input = $q->param('input');
    my @urls = split /[\r\n]+/, $input;
    my $fh = $q->upload('input_file');
    while (<$fh>) {
        my @line = split /[\r\n]+/;
        push @urls, @line;
        }
    for (@urls) {
        # Hinzufügen des Schemas
        $_ = "http://"; . $_ unless /^http/;
        my $browser = LWP::UserAgent->new( );
        # Um eine automatische Weiterleitung zu vermeiden: weitergeleitete URLs 
erscheinen als invalid!
        $browser->requests_redirectable([]) if ($q->param('no_redirect'));
        my $response = $browser->get($_);
        if ($response->status_line eq "200 OK") {
            print qq{<p><span style="color:green">'$_'</span> is valid</p>};
        }
        else {  
            print qq{<p><span style="color:red">'$_'</span> is not valid<br 
/><b>Response status:</b> }, $response->status_line, "</p>";
        }
    }
}
else {
# html form is displayed here
}

print $q->end_html;

___END CODE___

This checks all URLs passed to the script and prints them out at once. When I 
add $| = 1; somewhere near the top, it also seems to buffer the output. I would 
expect the lines to appear one after the other.

What am I doing wrong?

Thanks,

Jan
-- 
There are two major products that come out of Berkeley: LSD and UNIX. We don't 
believe this to be a coincidence. - Jeremy S. Anderson

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