#!perl -wl
use strict;

my $__item= 'abc_IoExtFscInjS_GetGlobalDatasetActvMethod';

warn $__item;
if ( ($__item =~ m/(?!Eth.+cfg)Eth/i) || ($__item =~ m/(?!abc_Eth.+cfg
+)abc_Eth/i) ) {
    print $`;
    print $&;
    print $';
    print "match";
} else {
    print "No match";
};
__END__
abc_IoExtFscInjS_GetGlobalDatasetActvMethod at tmp.pl line 6.
abc_IoExtFscInjS_GetGlobalDatasetActvM
eth
od
match
[download]

This had me stumped first, but when Perl claims it finds a match, it can also tell you, where :)