malaga has asked for the wisdom of the Perl Monks concerning the following question:

i'm trying to say that for each my $ref (@records ) if there is an entry for {qw/URL/}, then print 'Webpage'. i've been trying to say the "if" part in the first line, but not having any luck. here's what i have, but it prints 'webpage' whether or not it exists. (i've also tried if exists, btw) 
for my $ref ( @records ) {
    print "<B>", 'Webpage:', ' ', "</B>";
    print "<A HREF\= \"@{$ref}{qw/URL/}\">", @{$ref}{qw/URL/}, "</A>",
+ "<br>";

}

[download]

Replies are listed 'Best First'.
Re: if
by chipmunk (Parson) on Feb 13, 2001 at 23:58 UTC
    A simple approach: 
    for my $ref ( @records ) {
    if ($ref->{URL}) {
        print qq{<B>Webpage:</B> <A HREF="$ref->{URL}">$ref->{URL}</A>
+<br>};
    }
}

    [download]
    But I think you're asking for an approach that puts the check for URL in the foreach line: 
    for my $ref ( grep $_->{URL}, @records ) {
    print qq{<B>Webpage:</B> <A HREF="$ref->{URL}">$ref->{URL}</A><br>
+};
}

    [download]
    I combined the print statements into a single print of a single string, and used qq{} to avoid having to escape the double quotes.

    That's two ways to do it...

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[d/l]
[select]
Re: if
by epoptai (Curate) on Feb 14, 2001 at 00:05 UTC
    You should carefully study the source code of working scripts for examples of looping and matching, you will learn a lot! In the meantime pay close attention to the difference between this and your original code which lacked the 'if' condition: 
    foreach my $ref (@records){
 if($ref=~/URL/){
 print qq(<B>Webpage: </B><A HREF="$ref">$ref</A><br>);
 }
}

    [download]
[reply]
[d/l]
      i know it. i was trying to follow other scripts, but i wasn't able to apply it here. sorry bout that. i still get confused sometimes when i'm dealing with hashes, especially when i'm being rushed, which i am. thanks.
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Re: if
by MeowChow (Vicar) on Feb 14, 2001 at 00:13 UTC
    Is there any reason you are dereferencing your ref hash with a hash slice of one element? 
      @{$ref}{qw/URL/}

    [download]
    is just a convoluted way of saying: 
      $ref->{URL}

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    There may be some tricks to be played by returning a singleton list instead of a scalar, but I don't think you're looking for anything of that sort. 
       MeowChow                                   
               s aamecha.s a..a\u$&owag.print
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[d/l]
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      I swear there's a book somewhere teaching people a Bondage and Discipline version of Perl. This convoluted access syntax has shown up time after time in posts.

      Instead, make it all cute and fluffy with curly braces:      @{${ref}}{map{qw{URL}}} Just kidding
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[d/l]
      i knew that, and the code started out that way, but at a certain point i decided to leave it open for more than one field in each print line. but it doesn't make sense to me now and i just went in and changed them all. thanks.
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(sacked) Re: if
by sacked (Hermit) on Feb 14, 2001 at 00:12 UTC
    Try replacing qw with q or just single quotes. qw is used to return a list of words, and q is equivalent to using single quotes. Also, because we're looking for a single element in the hash, you don't need the hash slice notation. Now we have: 
    for my $ref ( @records ) {
  if ( $ref->{'URL'} ) {
    print qq(<B>Webpage:</B>) .
          qq(<A HREF="$ref->{'URL'}">$ref->{'URL'}</A><br>);
  }
}

    [download]

    --sacked
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[d/l]
Re: if
by malaga (Pilgrim) on Feb 14, 2001 at 00:06 UTC
    perfect. i was trying every which way, but couldn't get the reference right. thanks a lot.
[reply]

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