use strict;
my $str = '0 100 Continuity_PPMU_mV XSCI 140
1 100 Continuity_PPMU_mV XSCI 12
2 100 Continuity_PPMU_mV XSCI 76
3 100 Continuity_PPMU_mV XSCI 204
4 101 Continuity_PPMU_mV XSCO 139';
my $regex = qr/\s+\d+$/mp;
my $subst = '';
my $result = $str =~ s/$regex/$subst/rg;
print "The result of the substitution is' $result\n";
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html