Perl map doubt

Hello ,

Please can someone tell me what exactly happens when the below filehandler is chomped into an array and later mapped.

$lcpLog="logcopy\@".getTimestamp."\log";

open CFg ,"< $lcpcfg";
chomp(@cfg = <CFG>);
close CFG;

@cfg=grep { $_ ne ' ' } map { lc + (split /\s*\/\//) [0] } @cfg;

Please explain what happens in above line