#! perl -sw
use strict;
use List::Util qw[ max ];

my $first = <>;
my @ugly = <>;
my $last = pop @ugly;

my @bits = map[ m[(^\s+)(\S+)\s*=>\s*(\S+),\n] ], @ugly;
my $largest = max( map{ length( $_->[1] ) } @bits );

print $first;
printf "%s%-${largest}s => %s,\n", @$_ for @bits;
print $last;
[download]

Output:

C:\test>1159396
C:\test>1159396
%some_hash = (
               key => "value1",
               larger_key => "value2",
               even_larger_key => "value3",
             );
^Z
%some_hash = (
               key             => "value1",
               larger_key      => "value2",
               even_larger_key => "value3",
             );
[download]