It works for me,

$ perl -w -e'my$n1="-933";my$n2="-1039";my$dif=$n1-$n2;print $dif,$/'
106
$
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Figure out how the spurious characters are getting in and you'll find the solution.

And this reminds me of another reason why I don't use Data::Dumper. It defaults to being "efficient" and so doesn't actually 'dump' the variable contents, in an effort to avoid the arduous task of escaping all those weird characters. You have to go out of your way to tell Data::Dumper to "useqq" for it to actually dump strings in a fool-proof manner.

> perl -del
# ...
  DB<4> print Dumper("\c\\-10")
$VAR1 = '-10';

  DB<5> print Data::Dumper->new(["\c\\-10"])->Useqq(1)->Dump()
$VAR1 = "\34-10";

  DB<6>
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The unescaped CTRL-\ removed from the above output as how it would be displayed would depend on several things and it didn't even remain a CTRL-\ after being copy-n-pasted into the browser and converted to Latin-1 etc. anyway.

Update: Oh, I thought Zaxo had noted what "^\" represents but I see he didn't so, to be very clear, "^\" is how perl is safely dumping a single CTRL-\ ("\c\\") character in that warning, which is why my example code looks like it does. No, I didn't realize this when first viewing the warning.

- tye        

You are right, tye. Following your suggestion, and by doing this:

my $some_string = "0,-933";


$Data::Dumper::Useqq = 1;         
print Dumper ($some_string) ;

my ($id1,$n1) = split(",",$some_string);
#then do things with $n1 and $n2.
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It gives:

$VAR1 = "0,\34-933";
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So my questions are:
• How can this \34 comes, in the first place? Can we avoid that?
  My development is always under Linux/Unix platform. And those variable values are read from a file.
• How to remove this \34 character from $VAR?

Regards,
Edward

Your strings having a leading character, ascii 28 (also known as the field separator). I can reproduce your error messages and results as follows:

$n1 = "\x1c-933"; ## hex( 1c ) == 28 == ^\ == Field separator
$n2 = "\x1c-1093"; 

print $n1 - $n2;;
Argument "^\-1093" isn't numeric in subtraction (-) at (eval 6) line 1
Argument "^\-933" isn't numeric in subtraction (-) at (eval 6) line 1
0
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That doesn't explain how those characters are getting into your data, but it will give you something to look for. You could try dumping the string prior to spliting using unpack:

print unpack 'C*', $the_string;
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Is this data being read from a file or a device?

Is there any chance that the data is getting the unicode bit set?

$h{1, 2} = "hello";
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my %h;
$h{1, 2} = "hello";
$Data::Dumper::Useqq = 1;
print Dumper \%h;
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From perlvar:

$SUBSCRIPT_SEPARATOR
$SUBSEP
$;      The subscript separator for multidimensional array emulation. 
+If
        you refer to a hash element as

            $foo{$a,$b,$c}

        it really means

            $foo{join($;, $a, $b, $c)}
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That's exactly what I did. Thanks so much for pointing that out!
FunkyMonk+++

Regards,
Edward

Argument "^\-933" isn't numeric in subtraction (-) at mycode.pl line 1
+15.
Argument "^\-1039" isn't numeric in subtraction (-) at mycode.pl line 
+115.
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Since the error message indicates that the values include initial caret and backslash characters ("^\"), my first guess would be that something odd is happening when assigning a value to the string that is being split on "," -- or something is altering the two values after the split -- involving regular expression operations.

Show us more of the actual code that caused the error -- in fact, see if you can construct a minimal self-contained script that includes the relevant value assignments, the split and the subtraction, and generates the error.

As others have pointed out, the "boiled down" information you've shown so far would not cause this error.

Update: Following your update, now we know that $n1 is splitted out from $some_string. But, where the heck this $some_string came from? It's the ultimate source of the data you need to tell so we know how is the data originally or initially the first time it arrives to the perl interpreter or your script. Don't emulate by literally assinging it to a variable if that's not actually the case since we'll just get nowhere.

$ cat diff.pl
use strict;
use warnings;

my $n1 = '-933';  # the same result
my $n2 = '-1039'; # without quotes
my $diff = $n1 - $n2;
print "diff: $diff\n";

$ perl diff.pl
diff: 106

$ perl -V
Summary of my perl5 (revision 5 version 8 subversion 8) configuration:
  Platform:
    osname=linux, osvers=2.6.9-22.18.bz155725.elsmp, archname=i386-lin
+ux-thread-multi
    uname='linux hs20-bc1-6.build.redhat.com 2.6.9-22.18.bz155725.elsm
+p #1 smp thu nov 17 15:34:08 est 2005 i686 i686 i386 gnulinux '
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Perhaps you could show us an actual runnable sample that demonstrates the problem? You could start by modifying the following to the point where it doesn't work any more:

use strict;
use warnings;

my $some_string = "0,-933";
my ($id1, $n1) = split(",",$some_string);
my $dif = $id1 - $n1;

print $dif;
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Prints:

933
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Hmmm... when I tried your code it worked just fine and $dif had the value of 106. What version of Perl are you using? What is the actual context of the code?

Not knowing the context, you might consider doing something like:

my $dif = ( int $n1 ) - ( int $n2 );
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perl -e 'split//,q{john hurl, pest caretaker}and(map{print @_[$_]}(joi
+n(q{},map{sprintf(qq{%010u},$_)}(2**2*307*4993,5*101*641*5261,7*59*79
+*36997,13*17*71*45131,3**2*67*89*167*181))=~/\d{2}/g));'
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If I run your program as:

my $n1 = '-933';
my $n2 = '-1039';

my $dif = $n1 - $n2;
print $dif . "\n";
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I get "106" as an output, which seems to be what you want.

Btw, here I have:

C:> perl -v
This is perl, v5.8.8 built for MSWin32-x86-multi-thread
(with 50 registered patches, see perl -V for more detail)

Binary build 820 [274739] provided by ActiveState
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