I suppose this will work in any context but it seems to require more programming effort :-(

It's not that much effort :)   You could start with just the READLINE method, and add more functionality later, if the need should arise...

Here's a simple example implementing READLINE and PRINT functionality:

#!/usr/bin/perl

package MyFH;

sub TIEHANDLE {
    my $class = shift;
    return bless { @_ }, $class;
}

sub READLINE {
    my $self = shift;
    print "reading line from remote file $self->{file} ...\n";

    # ... (your implementation here)

    my $line = "foo\n";
    my @lines = ("foo1\n", "foo2\n");

    return wantarray ? @lines : $line;
}

sub PRINT {
    my $self = shift;
    print "writing line(s) to remote file $self->{file} ...\n";

    # ... (your implementation here)

    print "wrote: @_\n";
}


package main;

use Symbol 'gensym';

my $fh = gensym();  # get ref to anonymous glob

tie *$fh, "MyFH",  "file" => "foo.txt";

my $line = <$fh>;
print "read: $line\n";

print $fh "bar", "baz";
[download]

Outputs:

reading line from remote file foo.txt ...
read: foo

writing line(s) to remote file foo.txt ...
wrote: bar baz
[download]

(Similarly, you could make use of Tie::Handle / Tie::StdHandle)

 

Update: the benefit of using a tied filehandle would also be that you could more easily make your remote SSH connection handle act like a full-fledged drop-in replacement for a regular filehandle, so existing code making use of <$fh> and print $fh ..., etc. wouldn't have to be modified. This might not seem important now, but who knows when you'll need it...

While you can overload the diamond operator, attempting to override/redefine print would soon turn into a major show stopper. Problem is that the print built-in doesn't have a prototype, at least not one that you could express with Perl's current prototyping mechanism (for this reason prototype 'CORE::print' is returning undef, btw). Its implicit prototype has been coded right into Perl's parser. This means that you cannot write a regular Perl subroutine which would be treated syntactically like the built-in print. In particular you can't get the "comma being absent" after the $fh in print $fh @args to work as desired (you'd get a syntax error if you tried).  With a tied filehandle you don't have such problems.

Using a tied filehandle is the 'correct' approach as others have pointed out. It's not much work if you use the (more or less undocumented) Tie::StdHandle class in Tie/Handle.pm. Just subclass Tie::StdHandle and then implement the routines you need, probably OPEN and READLINE in your case.