system and pipes

FourierXForm has asked for the wisdom of the Perl Monks concerning the following question:

To the Brethren, I am trying to do the following shell equivalent in Perl:

$ /usr/bin/tar -cz /opt/back | /usr/bin/ssh myname@remote.host.com 'dd
+ of=/opt/rback/back.tar.gz'
[download]

Here is my Perl code:

my $tar = "/usr/bin/tar";
my $taropts = "-cz";
my $backupdir = "/opt/back";
my $ssh = "/usr/bin/ssh";
my $user = "myname";
my $remotehost = "remote.host.com";
my $remotedir = "/opt/rback";

my @args = ($tar, "$taropts", "$backupdir", "\|", $ssh, "$user\@$remot
+ehost", "'dd of=$remotedir/back.tar.gz'");

system(@args) == 0 or die "System @args failed: $!\n";
[download]

When I execute this code snippet, all the output goes to STDOUT. How do I get this to work. Thanks!

Comment on system and pipes Select or Download Code

Replies are listed 'Best First'.
Re: system and pipes by matija (Priest) on Jan 18, 2006 at 15:24 UTC
It is commendable that you're calling system with an array of references, because that avoids some of the shell exploits. However, since you intend to use shell redirection to accomplish your command, you can't do it this way. The easy way to do it would be: `system("$tar $taropts $backupdir \| $ssh $user\@$remotehost 'dd of=$rem +otedir/back.tar.gz'")` [download] The hard way would be starting tar in one process, the ssh/dd in another, and playing the IPC between them. Comparatively hard, for very little gain. In effect, you'd have to reimplement the shell redirects in order to do it. It's easier to just use the shell's redirects, and fortunately, Perl makes that possible.	[reply] [d/l]
Re^2: system and pipes by FourierXForm (Acolyte) on Jan 18, 2006 at 15:32 UTC
Thank you very much. It worked perfectly!!	[reply]
Re: system and pipes by glasswalk3r (Friar) on Jan 18, 2006 at 17:45 UTC
Despite it works using system() function as told before, you may want to test using Perl modules that implements the functions that you want (tar and ssh) instead of making systems calls. You will have more control of what is happening and making your program more secure too. Alceu Rodrigues de Freitas Junior --------------------------------- "You have enemies? Good. That means you've stood up for something, sometime in your life." - Sir Winston Churchill	[reply]
Re: system and pipes by Anonymous Monk on Jan 18, 2006 at 19:55 UTC
Why not just... `system("/usr/bin/tar -cz /opt/back \| /usr/bin/ssh myname@remote.host.com 'dd of=/opt/rback/back.tar.gz'");`	[reply] [d/l]
Re: system and pipes by svenXY (Deacon) on Jan 18, 2006 at 15:22 UTC
Hi, ~~just a rough guess, could it be that the second pipe (the one before the dd) is missing?~~ Regards, svenXY Update: Found his typo, but no solution to his problem...	[reply]
Re^2: system and pipes by FourierXForm (Acolyte) on Jan 18, 2006 at 15:26 UTC
I apologize as it was a mistake on my part. I had since corrected it :)	[reply]
Re: system and pipes by bravenmd (Sexton) on Jan 19, 2006 at 15:40 UTC
Seems easier to just use: system("$tar $taropts $backupdir \| $ssh $user\@$remotehost 'ddof=$remotedir/back.tar.gz'");	[reply]