«

I have written a function to log variables like this:

" varName: varValue"

but it takes two arguments: the variable name as a string, and the
variable symbol:

logVar ("myVar", $myVar) ;

sub logVar {
my $varName = shift ;
my $varValue = shift ;
if (!defined($varValue)) {
$varValue = "<undef>" ;
}
printf ("%16s: %s\n", $varName, $varValue) ;
}

Is there any way to get "myVar" from $myVar or vice versa, without
foregoing 'strict' and 'warnings'?

Note: My actual code uses Std::Log but the problem is the same.

Thanks,

Jerry Krinock

Jerry Krinock <> wrote in news:a2761c7e-8820-4f16-
98d7-:

> I have written a function to log variables like this:
>
> " varName: varValue"

This is a FAQ:

perldoc -q "How can I use a variable as a variable name"

Sinan

--
A. Sinan Unur <>
(remove .invalid and reverse each component for email address)

comp.lang.perl.misc guidelines on the WWW:
http://www.rehabitation.com/clpmisc/

A. Sinan Unur <> wrote:
> Jerry Krinock <> wrote in news:a2761c7e-8820-4f16-
> 98d7-:

> > I have written a function to log variables like this:
> >
> > " varName: varValue"

> This is a FAQ:

> perldoc -q "How can I use a variable as a variable name"

> Sinan

I think the OP is looking for something a bit different, i.e.
a way to get the name of variable from the variable itself.
I.e. some hypothetical code like

my $x = 10;
logvar( \$x );

sub logvar {
my $varref;
print get_name_from_reference( $var ) . " " . $$var . "\n";
}

It's clear that for something like this to work a reference to
the variable has to be passed to the function. But I have no
idea how to write a function like get_name_from_reference()
and also have my doubts that it is possible at all (but then
this is Perl and there's so much magic that it is hard to be
sure
Regards, Jens
--
\ Jens Thoms Toerring ___
\__________________________ http://toerring.de

On May 9, 1:21 pm, Jerry Krinock <je...@sheepsystems.com> wrote:
> I have written a function to log variables like this:
>
> " varName: varValue"
>
> but it takes two arguments: the variable name as a string, and the
> variable symbol:
>
> logVar ("myVar", $myVar) ;
>
> sub logVar {
> my $varName = shift ;
> my $varValue = shift ;
> if (!defined($varValue)) {
> $varValue = "<undef>" ;
> }
> printf ("%16s: %s\n", $varName, $varValue) ;
>
> }
>
> Is there any way to get "myVar" from $myVar or vice versa, without
> foregoing 'strict' and 'warnings'?
>
> Note: My actual code uses Std::Log but the problem is the same.
>
> Thanks,
>
> Jerry Krinock

sounds like you need the (non-existent) Perl func uneval()

Quoth Jerry Krinock <>:
> I have written a function to log variables like this:
>
> " varName: varValue"
>
> but it takes two arguments: the variable name as a string, and the
> variable symbol:
>
> logVar ("myVar", $myVar) ;
>
> sub logVar {
> my $varName = shift ;
> my $varValue = shift ;
> if (!defined($varValue)) {
> $varValue = "<undef>" ;
> }
> printf ("%16s: %s\n", $varName, $varValue) ;
> }
>
> Is there any way to get "myVar" from $myVar or vice versa, without
> foregoing 'strict' and 'warnings'?

You can do this with PadWalker. If you need more hints than that, you
probably shouldn't be trying...

Ben

--
I have two words that are going to make all your troubles go away.
"Miniature". "Golf".
[]

On May 9, 11:21*am, j...@toerring.de (Jens Thoms Toerring) wrote:

> I think the OP is looking for something a bit different...

Yes, I am.

On May 9, 10:43 am, "A. Sinan Unur" <1...@llenroc.ude.invalid> wrote:
> This is a FAQ:
>
> perldoc -q "How can I use a variable as a variable name"

I'd read that, and now studied it further, but I get the impression
that the only solution is to always define all of my variables in my
own hash, just in case I ever decided that I wanted to log one of
them.

That's not going to be any fun, and not very readable by earthlings.
Indeed, this code works:

#!/usr/bin/perl
use strict ;
use warnings ;

my %MY_VARS ;

# New Way to declare a Loggable Variable...
# Instead of just "my $fred",
# I now have to write:
my $fred = $MY_VARS{"fred"} ;

# New Way to assign a Loggable Variable
# Instead of just "$fred = 23",
# I now have to write:
$MY_VARS{"fred"} = 23 ;

# Well, after all that yuck, indeed, as desired,
# I can log it with only one argument, :

logVar("fred") ;

# Using this handy function
sub logVar {
my $varName = shift ;
my $varValue = $MY_VARS{$varName} ;
if (!defined($varValue)) {
$varValue = "<undef>" ;
}
printf ("%32s: %s\n", $varName, $varValue) ;
}

But it's hardly worth all that massive obfuscation. Can someone
confirm that there is indeed no way to simply log a "regular" variable
and its name without having to type both of them, or is Jens correct
that it can't be done?

Jerry

On May 9, 1:43*pm, "A. Sinan Unur" <1...@llenroc.ude.invalid> wrote:
> Jerry Krinock <je...@sheepsystems.com> wrote in news:a2761c7e-8820-4f16-
> 98d7-64c1bc9ef...@k13g2000hse.googlegroups.com:
>
> > I have written a function to log variables like this:
>
> > * * *" * * * * varName: varValue"
>
> This is a FAQ:
>
> perldoc -q "How can I use a variable as a variable name"
>

I don't think this is quite it...perhaps the Debugger's DumpPackages?
This displays the symbol tables of packages.

wrote in news:2643728c-7f39-43d9-8c46-
:

> On May 9, 11:21*am, j...@toerring.de (Jens Thoms Toerring) wrote:
>
>> I think the OP is looking for something a bit different...
>
> Yes, I am.

I jumped the gun, sorry!

Sinan

--
A. Sinan Unur <>
(remove .invalid and reverse each component for email address)

comp.lang.perl.misc guidelines on the WWW:
http://www.rehabitation.com/clpmisc/

On May 9, 12:37 pm, Ben Morrow <b...@morrow.me.uk> wrote:

> You can do this with PadWalker.

Thank you. I haven't tried it yet, but documentation of PadWalker
from CPAN declares a var_name() function that seems to be exactly what
I want.

Apparently this was a tricky feat. From the documentation: "I
wouldn't recommend using PadWalker directly in production code, but
it's your call. Some of the modules that use PadWalker internally are
certainly safe for and useful in production."

And from a review: "PadWalker is really, really useful if you need to
debug something really, really weird. I hope you never have to use
this module, but if you do, use it boldly."



Thanks for all the help. I'll probably give PadWalker a try next time
I am feeling bold, and have a little time to spare before production.

Jerry Krinock

>>>>> "j" == jerrykrinock <> writes:

j> On May 9, 12:37 pm, Ben Morrow <b...@morrow.me.uk> wrote:
>> You can do this with PadWalker.

j> Thank you. I haven't tried it yet, but documentation of PadWalker
j> from CPAN declares a var_name() function that seems to be exactly what
j> I want.

j> Apparently this was a tricky feat. From the documentation: "I
j> wouldn't recommend using PadWalker directly in production code, but
j> it's your call. Some of the modules that use PadWalker internally are
j> certainly safe for and useful in production."

j> And from a review: "PadWalker is really, really useful if you need to
j> debug something really, really weird. I hope you never have to use
j> this module, but if you do, use it boldly."

j>

j> Thanks for all the help. I'll probably give PadWalker a try next time
j> I am feeling bold, and have a little time to spare before production.

and i doubt you have a legit reason to need this in production code. i
smell an XY problem here. when someone needs to use such a dark magic
solution, i say the problem is poorly specified or similar. tell us what
the real problem is, don't ask how to do something requiring magic. i
can find no good reason (other than debugging or wacko stuff) for
needing the name of a variable. and if you have anon references, you
can't get any name.

uri

--
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