system(@ssh) steals stdin

[Marc Girod]

Hello,

Only partly a Perl question...

For some reason (don't ask...) I need to read data from stdin after
having invoked a program remotely, with ssh.
Surprise: there is nothing there...
Demo:

$ cat rsdtin
#!/usr/bin/perl -w

use strict;
use warnings;

my @ssh = qw(/usr/bin/ssh -q);
system(@ssh, qw(myhost /bin/date));
my @a = <>;
print "a: @a\n";
$ cat << eot | rstdin
aaa
bbb
eota:
$

Something I miss?
I thought of using Net::SSH:erl, but I had some problems to install
it (or some dependency) in a way which would work on both Solaris 8
and 10...

Thanks,
Marc

 

[Randal L. Schwartz]

Marc> Hello,
Marc> Only partly a Perl question...

Marc> For some reason (don't ask...) I need to read data from stdin after
Marc> having invoked a program remotely, with ssh.
Marc> Surprise: there is nothing there...

No surprise for me. In general, the child process started by system()
inherits Perl's stdin, stdout, and stderr. Your "ssh" is very likely
reading stdin in anticipation of sending it to the remote host.

If you tried the same trick with:

system "ssh myhost /bin/date </dev/null";

Or even:

system "date";

I'm sure you'd see a different output.

So it's not "system" stealing your input. It's ssh.

print "Just another Perl hacker,"; # the original

 

[Marc Girod]

I'm sure you'd see a different output.

I do.
Thanks!
Marc