Sometimes just modifying the input line with a very simple expression works out fine. In this case, apparently sometimes the "-", minus sign is sometimes not preceded by a space. A simple idea is to fix that in the input line (if it occurs). The code below does not modify the input line unless there is a negative number which is not preceded by a space.

Once a simple space separated token rule has been enforced, then a simple split statement suffices. I don't know if this is true in this case, but often running a couple of simple regex/split statements can execute faster than a single complicated regex. 

use warnings;
use strict;

while (my $line = <DATA>) 
{
  
   chomp $line;
   print "Input Line: '$line'\n";
   $line =~ s/(\S)-/$1 -/g;  # add space before minus if needed
                             # otherwise don't add a space
   print "Modified Line: '$line'\n";
   my @numbers = split ' ', $line;
   print "Numbers are @numbers\n\n";
}

=prints:

Input Line: '1.234 5.6789 -1.235-4'
Modified Line: '1.234 5.6789 -1.235 -4'
Numbers are 1.234 5.6789 -1.235 -4

Input Line: '1.234 5.6789-12.235-4'
Modified Line: '1.234 5.6789 -12.235 -4'
Numbers are 1.234 5.6789 -12.235 -4

=cut


__DATA__
1.234 5.6789 -1.235-4
1.234 5.6789-12.235-4

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In reply to Re: match digit, followed by hyphen, followed again by digit - then add whitespaces and replace in file by Marshall
in thread match digit, followed by hyphen, followed again by digit - then add whitespaces and replace in file by fasoli

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