G'day thanos1983,

Instead of using intermediary variables, you could do this:

my %hash = ((split / /, $str), $str =~ y/ / / % 2 ? () : undef);
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I tested this on the command line. Sorry about the wrapping.

$ perl -wMstrict -MData::Dump -e 'my $s = "a 1 b 2 c 3 Odd"; my %h = (
+(split / /, $s), $s =~ y/ / / % 2 ? () : undef); dd \%h'
{ a => 1, b => 2, c => 3, Odd => undef }
$ perl -wMstrict -MData::Dump -e 'my $s = "a 1 b 2 c 3 Even 4"; my %h 
+= ((split / /, $s), $s =~ y/ / / % 2 ? () : undef); dd \%h'
{ a => 1, b => 2, c => 3, Even => 4 }
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See "perlop: Quote-Like Operators" if you're unfamiliar with using y/// for counting.