$item = 05540986;  #do not change!

 my @list=qw(05540987 05540984 05540982 05540981 05540986 05540983 05540991 05540985 05540990 05540989 05540988 05540992 );
 my %lookup;@lookup{@list} = (1..@list);


 $IDposition = $lookup{$item};

 print " $item is located at index $IDposition \n";