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variable with $$

by Anonymous Monk
on Apr 08, 2004 at 04:27 UTC ( #343493=perlquestion: print w/ replies, xml ) Need Help??
Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

hello monks , I have a variable like that : 
my $name = Sam;

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what I wanna do is create a variable from reading $name which will look like this : 
my $newvar = $Sam;

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so I want to print the value for name with a $ in the front of it. I tried : 
my $newvar = $\"$name";
or 
my $newvar = '$'"$name";

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no luck ,, any idea? can someone help? thanks

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Re: variable with $$
by asarih (Hermit) on Apr 08, 2004 at 04:51 UTC
    
$var="test";
$test="fred";
print ${$var};


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    update Note to self: read thoroughly before post.
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Re: variable with $$
by The Mad Hatter (Priest) on Apr 08, 2004 at 04:52 UTC
    Put $name in double quotes and then backslash (escape) the extra $... 
    my $name = "Sam";
my $newvar = "\$$name";
# or even ... my $newvar = '$' . $name;

print $name, "\n", $newvar;

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    which prints 
    Sam
$Sam

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Re: variable with $$
by Steve_p (Priest) on Apr 08, 2004 at 04:54 UTC

    Try...

    my $newvar = "\$" . "$name";
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Re: variable with $$
by kvale (Monsignor) on Apr 08, 2004 at 04:56 UTC
    You can do this with 
    my $name = "Sam";
my $newvar = '$' . $name;

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    -Mark

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      thanks all
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Re: variable with $$
by bart (Canon) on Apr 08, 2004 at 10:56 UTC
    You're asking for symbolic references, huh? At least, I think you are. Well: don't do it, unless you know really well what you're doing — and basically, if you have to ask how to do it, I dare to bet that you don't. Making a name based on a user's input is always very dangerous. You never know whether he'll input the name of a variable you've used yourself in your program.

    See dominus' classic 3 articles on his website, for more arguments against it:

    1. Why it's stupid to `use a variable as a variable name'
    2. A More Direct Explanation of the Problem
    3. What if I'm Really Careful?

    In general: don't do it. Use a hash. Like this: 

    my %v;   # my hash for user variables
$v{Sam}++; 
# or:
my $name = 'Sam';
$v{$name}++;

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    Oh, and if you really want to do it, try $$name or ${$name}, which both do the same thing, and only work on global (= package) variables — and only with no strict 'refs'. Just to show you it can be done... ;-)

    If all you want is to work on predefined variables with no input from the user/outside world, try hard references instead. 

    my $var = \$sam;
$$var++;  # increments $sam

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    Yes, the syntax is exactly the same. That's one reason why coding without strict 'refs' in place, is a rather bad idea.
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Re: variable with $$
by zentara (Archbishop) on Apr 08, 2004 at 13:24 UTC
    Yep, it is far from my lowly status to say that Bart is right, but he is. Whenever you start thinking about using a "variable in a variable" just stop!!...and think how can I do this with a hash? It will save you tons of trouble, and once you get the "hang of hashes", you'll love them.
    I'm not really a human, but I play one on earth. flash japh
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