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

Dear fellow monks, I have this script that reads a rather lengthy text file line by line and extracts information from it.
While developing I want to see the values that are put into different variables at the time, so I print them out to STDOUT.

So far everything is fine. But I do get a lot of "Use of uninitialized value in concatenation (.) or string" warnings because the values are in fact uninitialized. The way I got rid of the warnings is: 
    {
        no warnings "uninitialized";
        print "var1=$var1 -- var2=$var2 -- var3=$var3\n";
    }

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This looks just a bit clumsy to me. Is there a better way to achieve this?

si_lence

Replies are listed 'Best First'.
Re: no uninitialized warnings
by herveus (Prior) on Aug 25, 2004 at 13:06 UTC
    Howdy!

    What do you want displayed when the variable is uninitialized? Your approach is straightforward and clear.

    Data::Dumper provides another mechanism that will show uninitialized values as "undef" without requiring you to write lots of code.

    yours,
    Michael
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Re: no uninitialized warnings
by ccn (Vicar) on Aug 25, 2004 at 12:46 UTC

    Why don't you just initialize them? 

    $_ ||= '' for $var1, $var2, $var3;    
print "var1=$var1 -- var2=$var2 -- var3=$var3\n";

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    or 
    print "var1=", $var1 || '', " -- var2=", $var2 || '', " -- var3=", $va
+r3 || '',  "\n";

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      Danger, Will Robinson. Danger!

      If $var1 has the value 0, it will be set to '', which might not be what you want.

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        Mh... something like this?

        @x=(1..3) ;
undef $x[1] ;
$_ = defined $_? $_: '[__UNDEF__]' for @x ;
print "@x" ;

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        Ciao!
        --bronto

        The very nature of Perl to be like natural language--inconsistant and full of dwim and special cases--makes it impossible to know it all without simply memorizing the documentation (which is not complete or totally correct anyway).
        --John M. Dlugosz
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      If the values might be uninitialized in the normal course of operation, and it's acceptible, then I see no problem just turning off the warning, as the OP has done. This is Perl, after all. The language should do what we want, not the other way around. :-)

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Re: no uninitialized warnings
by Forsaken (Friar) on Aug 26, 2004 at 09:56 UTC
    well, i'm one of those people that considers warnings blasphemy, so i avoid them like the plague. In a case like this I'd simply use something like:

    print "some sort of introduction of the following comes here";
    if($var1) { print "\$var1 = $var1 "; }
    if($var2) { print "\$var2 = $var2 "; }
    if($var3) { print "\$var3 = $var3"; }
    print "\n";

    perhaps i'm allowing the quirks of the language to dominate my style here, but I have all my bases covered this way :-)

    Additionally, I tend to encapsulate a construction like this in a if($debug) {} so as to allow me to turn all the debug messages in a script on or off with the change of a single variable somewhere.
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Re: no uninitialized warnings
by si_lence (Deacon) on Aug 26, 2004 at 12:29 UTC
    Thanks for all the input! I used Data::Dumper to print out larger data structures, but using it to print out the names is very nice too. 
        print Data::Dumper->Dump([$var1, $var2, $var3], [qw($var1 $var2 $v
+ar3)]);

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    Speaking of a $debug switch to print out information only while debugging:
    I usually use an if statement modifier so I can use more than one level of verbosity 
       my $v=0; #0 for silent, 1 for main info, 2 for all info

   ...
   print "something important\n" if $v > 0;
   print "something not so important\n" if $v >1;

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    si_lence
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