Perl execute SQLCMD with variables

I need to pass variables to the SQLCMD command. I have the following script:

#! /usr/bin/perl 
use strict;
use POSIX qw(strftime);
use Config::IniFiles;
my $TODAY = strftime "%Y%m%d", localtime;
my $cfg = Config::IniFiles->new( -file => 'test.ini' );
my @db = $cfg->Sections;

for my $dbs (@db){
  my $IP=$cfg->val($dbs,'ip');
  my $PORT=$cfg->val($dbs,'port');
  my $USER=$cfg->val($dbs,'user');
  my $PASS=$cfg->val($dbs,'pass');
  my $DB=$cfg->val($dbs,'pass');
  my $MOTOR=$cfg->val($dbs,'motor');
  my $INSTANCIA=$cfg->val($dbs,'instancia');
  my $PATH=$cfg->val($dbs,'path');
  my $DUMP=$PATH . "Backup_Test_" . $TODAY . ".bak";
  'sqlcmd -S $IP,$PORT -U $USER -P $PASS -Q "BACKUP DATABASE [$DB] TO DISK='$DUMP'"}';
  if($? == 0){
    print "0\n";
  }
  else{
    print "Error\n";
  }
 }

How I do it so that the sqlcmd takes the values of these variables. I have tried several combinations but I still can not perform database backup and I get a 0 as a result, the command was executed well but the dump is not generated ...?.