• The first error means the value against which you are matching is undef. The value against which you are matching is data_verify's first argument. That situation is not possible in the code you posted.

  There are numerous places where undefined could be passed to data_verify in the code on your scratchpad.

• The second error is caused by your use of the $/ in your pattern while that variable is undefined. m{s/\s*$//}xms means

  • Match the two characters 's/',
  • followed by any number of spaces,
  • followed by the pattern held by $/,
  • followed by the character '/'.

  Obviously not what you wanted. For starters, you wanted to do a substitution rather than a match. m{s/\s*$//}xms should be just s/\s*$//.

  sub data_verify {
   my @data = shift;
   my $loop_count = 0;
   while (@data) {
    $data[$loop_count] =~ s/^\s*//;
    $data[$loop_count] =~ s/\s*$//;
    $loop_count++;
   }
   return @data;
  }
  [download]

By the way,

sub data_verify {
 my @data = shift;
 my $loop_count = 0;
 while (@data) {
  $data[$loop_count] =~ s/^\s*//;
  $data[$loop_count] =~ s/\s*$//;
  $loop_count++;
 }
 return @data;
}
[download]

is equivalent to

sub data_verify {
 my $data = shift;
 $data =~ s/^\s*//;
 $data =~ s/\s*$//;
 return $data;
}
[download]

Based on the code in your scratchpad, you want to process multiple values per call. What you really want is

sub data_verify {
 my @data = @_;
 for (@data) {
   s/^\s*//;
   s/\s*$//;
 }
 return @data;
}
[download]