returns a list of directory entries, each of which is a reference to a hash as described in the previous paragraph.

Where the previous paragraph says:

a hash with three keys: filename, the name of the entry in the directory listing; longname, an entry in a "long" listing like ls -l; and a, a Net::SFTP::Attributes object, which contains the file attributes of the entry (atime, mtime, permissions, etc.).

So, if you want to assign to a hash, you need to dereference first:

for my $remote_file ($sftp->ls('.')) {
    my %details = %$remote_file;
     print $details{filename}, "\n";
}
[download]

To visualize the whole structure, use Data::Dumper:

use Data::Dumper;
for my $remote_file ($sftp->ls('.')) {
    print Dumper($remote_file);
}
[download]

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]