[18:25][nick:~/monks]$ cat 1135741.pl 
#! perl -w
use strict;
use feature qw/ say /;

use Path::Tiny qw/ path /;

my $file = 'test.dat';
my @lines = path( $file )->lines( { chomp => 1 } );

# do something with @lines ...

my @append = (); # empty array
path( $file )->append( @append, { truncate => 1 } );

say "Done.";

__END__

##</code><code>##

[18:25][nick:~/monks]$ cat test.dat
foo
bar
baz
quux

##</code><code>##

[18:26][nick:~/monks]$ perl 1135741.pl 
Done.

##</code><code>##

[18:26][nick:~/monks]$ cat test.dat
[18:26][nick:~/monks]$