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

Example 
$var1 = 7;
$var2 = 3;
foreach $number(1..2) {
  print $var${number} . "\n";
}

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this doesn't work....docos are bare on this....how to construct variable names on the fly?

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Re: construct variable name on the fly
by Fletch (Bishop) on Oct 19, 2004 at 00:44 UTC

    They don't really mention it because it's a bad idea. In your case you want an array @var; in the more general class you'd use a hash. See perldoc perlref for discussion about symbolic references.

    Update: See also Program Repair Shop and Red Flags (and while not directly relevant there's another two Red Flag articles here and here that are well worth checking out).

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      i know it's a bad idea.....and i will rectify when i have time. right now i have a report overdue (work) and need to get it going. Any help on getting the keys from a hash whose name is constructed from other variables would be appreciated. e.g. keys %this.${somevar}.name; doesnt work.
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Re: construct variable name on the fly
by Juerd (Abbot) on Oct 19, 2004 at 20:44 UTC
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Re: construct variable name on the fly
by nedals (Deacon) on Oct 19, 2004 at 06:49 UTC
    In direct response... but it will not work under 'strict' 
    $var1 = 7;
$var2 = 3;
foreach $number(1..2) {
    $varname = 'var'.$number; 
    print $$varname."\n";
}

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    Or you could use a hash 
    use strict;
my %var;
$var{1} = 7;
$var{2} = 3;
foreach my $number(1..2) {
    print $var{$number}."\n";
}

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Re: construct variable name on the fly
by TedPride (Priest) on Oct 19, 2004 at 14:04 UTC
    print ${"var$_"}."\n" for (1..2);

    ${'var1'} gives the same results as $var1.

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Re: construct variable name on the fly
by aquarium (Curate) on Oct 19, 2004 at 01:11 UTC
    thank you....the dot operator did the trick. this doesn't work for getting keys from such a constructed variable though. Any help in this regard please. Example: 
    $thisname{'frank'} = 1;
$thisname{'lee'} = 2;
$hashname = 'thisname';
print keys %.$hashname;

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      $thisname{'frank'} = 1;
$thisname{'lee'} = 2;
$hashname = 'thisname';
print keys(%$hashname);

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Re: construct variable name on the fly
by bradcathey (Prior) on Oct 19, 2004 at 00:39 UTC

    Here's a method, but it doesn't work under strict.

    {
   no strict 'subs';        
   foreach $number(1..2) {
      print $var.$number . "\n";
   }
}

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    Update: Oops, a little too fast on the draw. I confused it with populating HTML::Template params. Way off!

    {
   no strict 'subs';        
   foreach $number(1..2) {
      $template ->param(
         var.$number     => $somevalue );
   }
}

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    So, Fletch is absolutely correct on both accounts.


    —Brad
    "Don't ever take a fence down until you know the reason it was put up." G. K. Chesterton
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      Whatever you posted before your update, or after, why no strict 'subs' has anything to do with the problem.What you want to mention is really 'refs'.

      This works:

      $thisname{'frank'} = 1;
$thisname{'lee'} = 2;
$hashname = 'thisname';
print keys(%$hashname);

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      This works:

      use strict('subs');
$thisname{'frank'} = 1;
$thisname{'lee'} = 2;
$hashname = 'thisname';
print keys(%$hashname);

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      This does not work:

      use strict('refs');
$thisname{'frank'} = 1;
$thisname{'lee'} = 2;
$hashname = 'thisname';
print keys(%$hashname);

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      No, that doesn't work even under strict. ${ "var$number" } would, but again symbolic references are bad practice.

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