If you really want to interact with the sftp cli, I think Expect is nearly always a better choice than IPC::Open2 or IPC::Open3. That being said, however, there is an sftp option that can make this a lot easier with just backticks...

open( OUT, ">/tmp/sftp-batch" );
print OUT <<"END";
cd foo
ls
END
close( OUT );

chomp( my @files = `sftp -b /tmp/sftp-batch hostname` );
open(OUT, ">/tmp/sftp-batch-2" );
print OUT <<"END";
cd foo
lcd bar
END
for my $file ( @files ) {
    print OUT "get $file\n";
}

system( "sftp -b /tmp/sftp-batch-2 hostname" );
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