~$ perl -E 'my @x=({uno=>'one'},{dos=>'two'},{tres=>'three'}); map {say}  keys %$_ for @x'

##</code><code>##

~$ perl -E 'my @x=({uno=>'one'},{dos=>'two'},{tres=>'three'}); say  keys %$_ for @x'

##</code><code>##

~$ perl -E 'my @x=({uno=>'one'},{dos=>'two'},{tres=>'three'}); say for  keys %$_ for @x'
syntax error at -e line 1, near "$_ for "