#!/usr/local/bin/perl -w
use strict;

open (FILE_MAKE_ERR, "make.err");

while(my $line = <FILE_MAKE_ERR>)
{
   if($line =~ /(ERROR|error)/ && $line !~ /errors/)
   { 
       $line =~ / (ERROR|error)\s+in\s+(\w+)\s+/;
       $line = $2;
       print "$line\n";
   }
}

$line =~ /(ERROR|error)\s+in\s+([\w\/]+)\s+/;

#!/usr/local/bin/perl

use strict;
use warnings;

open (FILE_MAKE_ERR,'<', "make.err") or die $!;

while(my $line = <FILE_MAKE_ERR>)
    if(my ($test) = $line =~ /(?i:error)\s+in\s+([^\s]+)/){
        print $test,"\n";
    }
}

close FILE_MAKE_ERR;

ERROR in freeware/lib/lib_nt.mak (lib). See /net/test.i18Global/file.err
error in test/path/test.mak (lib)
test error

123> perl regex.pl 
freeware/lib/lib_nt.mak
test/path/test.mak

/(?i:error(?!s))\s+in\s+([^\s]+)/