I suspect it is not perl that is sending the string but your script or the module you are using. In that case it would be very helpful to know this script and/or the modules your are using.

Similar to the particle-wave duality in physics you could say that there is a string-number duality in perl. You can't test a variable whether it is a number or a string because it is both. Ok, you can use a regex and find out that there is nothing in a string that looks like a number, but the following just works (and would at most print a warning message if you turn on warnings):

> perl -e 'print 1+"buss";'
1
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If the module you are using is doing some automatic testing with regexes, you might have luck with just adding a space to your string. Otherwise there must be something to specify the type

If you're using XML::RPC, this should work:

sub as_string { 
   my $val = shift;
   return sub {   { string => $val };   };
}
...

$xmlrpc->call( 'gimmeallyourmoney', { cardnumber => as_string( 12345 )
+ } );
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Which generates:

<?xml version="1.0" encoding="UTF-8" ?>
<methodCall>
<methodName>gimmeallyourmoney</methodName>
<params>
<param>
<value>
<struct>
<member>
<name>cardnumber</name>
<value>
<string>12345</string>
</value>
</member>
</struct>
</value>
</param>
</params>
</methodCall>
[download]

Update: Added patch to XML::RPC-wishlist.

Its a free download, full of useful tips.

my $numeric_x = 0 + $x;  # forces numeric context

my $stringy_x = '' . $x; # forces string context

my $boolean_x =    !!$x; # forces boolean context
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Showing us some code would help.

I was bit by a similar situation doing XML RPC to a Java based server that was asking for a boolean. I used RPC::XML to make the XML RPC process easy and ultimately solve the problem.

In your case, the method would be something like:

RPC::XML::string->new(12345)
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