Are you wanting to add the last line to the top and get rid of it at the bottom? Or just add last line to the top and keep rest of the file as is? I suggest you make a backup on you own before you try using this (if you do use it)

This will leave the last line in the file while putting it at the beginning as well:

use strict;
use warnings;

my @array;

open( my $orig,   '<', 'original_file' );
open( my $backup, '+>', 'original_backup' );

while (<$orig>) {
    push ( @array, $_ );
    print( $backup $_ );
}

close($orig);

open( my $new_orig, '+>', 'original_file' );

print( $new_orig $array[-1] );
print( $new_orig @array );

close( $new_orig );
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This will copy the last line to the beginning while removing it from the end

use strict;
use warnings;

my @array;

open( my $orig,   '<',  'original_file' );
open( my $backup, '+>', 'original_backup' );

while (<$orig>) {
    push( @array, $_ );
    print( $backup $_ );
}

close($orig);

open ( my $new_orig, '+>', 'original_file' );

print( $new_orig pop @array );
print( $new_orig @array );

close ( $new_orig );
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Sample input data:

is
a
test!!!
this
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