http://qs321.pair.com?node_id=1095329

ghosh123 has asked for the wisdom of the Perl Monks concerning the following question:

Hi monk,
I am working with a Perl which looks like below : 


  sub display {
                $self = shift;
                if(exists $error){
                  $html .= "<table border=0>";
                  $html .= "<tr>";
                  $html .= "<td align=center ><b>".$self->     {error}
+."</b></td>";
                  $html .= "</tr>";
                  $html .= "</table><br>";
           }
     
                 $html .= <<END;
     
                    <table border=0>
                    <tr>
                   <th bgcolor="#CCCCEE">Name</th><th>&nbsp;     </th>
+<th bgcolor="#CCCCEE">Address</th>
                   </tr>
        
                   <tr align=center>
                   <td bgcolor="#EEEEEE">@{[ $qry->popup_menu(-id=>'ID
+', -name=>'PS', -size=>10, -values=>$array_ref, -labels=>$hash_ref,  
+-onChange=>"fetchData(id,'','','')") ]}</td>
   
                   </tr>
                </table>

END

return $html;

}

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In the above code, what does this <<END and END mean ?
how can I change the code which is in between that <<END and END, to insert a if-else condition for that popup_menu.

To clarify further, depending on some values passed to that function, I want another popup_menu which will have a onload function instead of onChange.
In this above code, how can I do that by writing a if-else condition.

Replies are listed 'Best First'.
Re: a perl code syntax help
by Discipulus (Canon) on Jul 28, 2014 at 11:09 UTC
    hello, you are facing a so called here-doc declaration: you can find more on this here

    You cannot insert a conditional statemenent in an such a construction.
    But you can easyly wrap the assignement in a conditional: 
    ##not tested

if ($a){$html .= <<END;
  
  #here case A  

END
}
else{$html .= <<END;
  
  #here case B or default  

END


}

    [download]

    HtH
    L*
    There are no rules, there are no thumbs..
    Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.
[reply]
[d/l]

      "You cannot insert a conditional statemenent in an such a construction."

      I beg to differ!

      use strict;
use warnings;

print <<"END" for 1..100;
@{[$_%3?():"Fizz",$_%5?():"Buzz",$_%5&&$_%3?$_:()]}
END

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      For simpler examples, it's even possible to make it sort of legible!

      use strict;
use warnings;

print <<"END" for 1..100;
@{[  ($_ % 2) ? 'Odd' : 'Even'  ]}
END

      [download]
      toby döt ink
[reply]
[d/l]
[select]
        ehehe i had some precognition when i wrote that..
        Better i would say: 'I tried but it was a...' but in Perl many many things are possible!

        Thanks tobyink
        There are no rules, there are no thumbs..
        Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.
[reply]
[d/l]

      thanks for your reply and pointer to the doc.
      I just do not want to write the same code again and again, can I write a function and pass 'onload' or 'onChange' in a variable? so that it would resolve the $func value as -onChange or -onload ?

[reply]

        You could make life much easier for yourself by using a templating system rather than creating HTML in this manner, but you already know that.

[reply]
        Yes, we can. Like that (untested): 
        ...
my $trigger = 'onload';

                 $html .= <<END;
...
                   <td bgcolor="#EEEEEE">@{[ $qry->popup_menu(-id=>'ID
+', -name=>'PS', -size=>10, -values=>$array_ref, -labels=>$hash_ref,  
+-${trigger}=>"fetchData(id,'','','')") ]}</td>
   
                   </tr>
                </table>

END

        [download]
        The original code did already interpolate a list expression in the heredoc string (@{[ ... ]} was already present). So you just have to replace the fixed text part (onChange) in the above expression (...) with a string variable (here I used $trigger).
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[d/l]
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Re: a perl code syntax help
by kcott (Archbishop) on Jul 28, 2014 at 11:32 UTC

    G'day ghosh123,

    "In the above code, what does this <<END and END mean ?"

    The construct 

    <<END;
...
END

    [download]

    is called a heredoc.

    Simplistically, it's just a string. In perlop, it's introduced in "Quote and Quote-like Operators" with a lot more detail in "Quote-Like Operators".

    "how can I change the code which is in between that <<END and END, to insert a if-else condition for that popup_menu."

    Now that you know that's a string, you probably won't be trying to do that any more. :-)

    I'd suggest something along these lines: 

    my $popup_string;

if (some_condition()) {
    $popup_string = ...;
}
else {
    $popup_string = ...;
}

$html .= <<END;
...
<td bgcolor="#EEEEEE">$popup_string</td>
...
END

    [download]

    -- Ken

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[d/l]
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Re: a perl code syntax help (ppi_dumper, wxPPIxregexplain.pl
by Anonymous Monk on Jul 28, 2014 at 20:44 UTC
[reply]
[d/l]

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