Interpolating inside Net::DNS

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

Hy all,

I'm writing some code to allow a user to delete/create/update DNS records. I'm using Net::DNS for the hard work...
here's an excerpt from an example from the Net::DNS documentation

$update->push(update => rr_add('foo.example.com. 86400 A 192.168.1.2')
+);
[download]

Now I have replcaed the 'rr_add' with '${var1}', but this doesn't seem to work; compilation errors

syntax error at ./djeezycl.pl line 120, near "{$var1}("
[download]

The only way it seems to interpolate is when I use concatenation, but than the rest of the line is treated as 1 string and Net::DNS can't locate that "class"
It should only look for 'rr_add', which doesn't interpolate when placed inside '$var1'.

I hope i'm making some sort of sense here...
Any help much appreciated :)

bye,
Roghue

Comment on Interpolating inside Net::DNS Select or Download Code

Replies are listed 'Best First'.
Re: Interpolating inside Net::DNS by sgifford (Prior) on May 10, 2004 at 23:43 UTC
`rr_add` is the name of a function, right? And you're putting a different function name in `$var1`? This isn't a simple case of interpolation, because it modifies the flow of your program. That's not to say you can't do it, of course. You can either use `eval`, as in: `$var1=rr_add $update->push(update => eval "${var1}('foo.example.com. 86400 A 192.16 +8.1.2'))");` [download] or else you can use a symbolic reference: `no strict 'refs'; $var1=rr_add $update->push(update => $var1->('foo.example.com. 86400 A 192.168.1.2' +))");` [download] Both of these code snippets are untested, but they should get you pointed in the right direction.	[reply] [d/l] [select]
Re: Re: Interpolating inside Net::DNS by Roghue (Initiate) on May 11, 2004 at 19:52 UTC
You were right, it worked like a charm with the symbolic reference. I never had the need to go further than using the ${} when interpolating in my scripts... untill now :) Thnx for that. bye, Roghue	[reply]
Re: Interpolating inside Net::DNS by Sidhekin (Priest) on May 10, 2004 at 23:47 UTC
`rr_add` is a subroutine, and your `$var1` contains its name. You are on your way to symbolic references. Which is probably a bad thing for someone who does not know the correct syntax for symbolic references ... To answer your question: If you want to use your symbolic reference to a subroutine as a function, you need to dereference it as a function. `# Either deref with ->(): $var1->('foo.example.com. 86400 A 192.168.1.2') # ... or, less fancy, deref with sigil: &{$var1}('foo.example.com. 86400 A 192.168.1.2')` [download] ... and so I have probably given you enough rope to hang yourself ... :-\ Actually, this is one of those places where I just might use symbolic references. If you can forever trust `$var1`, that is. If that is not the case, you might do better to use a lookup table with real references. `print "Just another Perl ${\(trickster and hacker)},"` The Sidhekin proves Sidhe did it!	[reply] [d/l] [select]
Re: Interpolating inside Net::DNS by tachyon (Chancellor) on May 10, 2004 at 23:51 UTC
What you are trying to do is use a symbolic reference. This is almost always a bad idea. You should use a dispatch table or even a series of if/elsif statements. You could do it using eval but that is dangerous unless you know what you are doing. You can do it like this provided you turn off strict: `no strict 'refs'; my $var1 = 'foo'; &$var1('Roghue, symbolic refs are bad practice'); sub foo { print "Hello $_[0]\n" }` [download] cheers tachyon	[reply] [d/l]