executing commands and getting output

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

Hi Perl Monks,
Need help with your wise advice here.

I was trying to run a daemon in a server, and I need to execute commands to get information regarding what active nodes is running in the server(for a specific application, particularly Netsolve), in order to then kill or restart the nodes (must be done one by one).

I was trying to use exec and system command, but with this, I could not get the output from the application, since I need them for deciding the subsequent actions in the program and also to update clients connected to the server regarding what's going on in the server.(The connection to clients are using IO::Socket::INET)

Can you give me suggestion to do this? ( execute command, get response from the application, and based on this response,execute different kinds of commands)

A bunch of thanks to you all.

Comment on executing commands and getting output

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Re: executing commands and getting output by zby (Vicar) on Sep 05, 2003 at 07:16 UTC
You should investigate the `open` function (using a "\|" in the file name). Or you could use the backtics: $output = `command`.	[reply] [d/l] [select]
Re: Re: executing commands and getting output by tja_ariani (Acolyte) on Sep 05, 2003 at 08:02 UTC
Hi, I tried the $output = 'command' method but it doesn't seem to work. $output is empty and does not contain anything. With the open command, could you give me a clue of what does it actually do ? Thanks for your help	[reply]
Re: Re: Re: executing commands and getting output by rnahi (Curate) on Sep 05, 2003 at 08:29 UTC
$output = `command`; # ^ ^ # \| \| [download] The quotes around command are backticks (ASCII 96, hex 60), not single quotes. As an alternative, you may use `$output = qx(command);` [download]	[reply] [d/l] [select]
Re: executing commands and getting output by bm (Hermit) on Sep 05, 2003 at 09:10 UTC
Use backticks. This only captures STDOUT, so you should add shell redirection to capture any errors that appear on STDERR: my $cmd = '/this/is/a/command -sdfw'; my $result = `$cmd 2>&1`; do_something() if ($result =~ /regex/); [download] see `perldoc -q capture` -- bm	[reply] [d/l] [select]
Re: executing commands and getting output by Roger (Parson) on Sep 05, 2003 at 11:02 UTC
Assume your command will return code on STDOUT or STDERR. Then you could simply do: my $result = `program`; # for collecting data from STDOUT [download] and my $result = `program 2>&1`; # for collecting data from STDERR. [download] There is no need to redirect the file handle. In the second case, the `2>&1` directive tells the shell to redirect all the output of program's STDERR (file handle 2) to STDOUT (file handle 1), so your perl program can collect the output of it.	[reply] [d/l] [select]
Re: executing commands and getting output by ctilmes (Vicar) on Sep 05, 2003 at 11:29 UTC
As already mentioned, backtics (`) will do the basics. If you want to do fancy stuff with stdin/stdout/stderr, etc. take a look at IPC::Run which provides some great mechanisms for perl interactions with background processes.	[reply]
Re: executing commands and getting output by jmanning2k (Pilgrim) on Sep 05, 2003 at 13:53 UTC
There's 3 options detailed for you in this post. Give them a try.	[reply]
Re: executing commands and getting output by gilbert0 (Monk) on Sep 05, 2003 at 16:24 UTC
If you want to see the output of the text, your best option is the Pipe. Ironicly i just asked rfp for some advice about his 'Pesky Pipe' problem so i can give you the example script and output: [root@wicca /root]# cat ppipe.pl #!/usr/bin/perl open(FILE,"/bin/netstat\|") \|\| die("can't open"); while(<FILE>){ print $_; } close(FILE); [root@wicca /root]# perl ppipe.pl Active Internet connections (w/o servers) Proto Recv-Q Send-Q Local Address Foreign Address St +ate tcp 0 0 10.9.205.4:netbios-ssn aeon-gig:1028 ESTAB +LISHED tcp 0 0 10.9.205.4:ssh aeon-gig:4931 ESTAB +LISHED Active UNIX domain sockets (w/o servers) Proto RefCnt Flags Type State I-Node Path unix 5 [ ] DGRAM 644 /dev/log unix 2 [ ] DGRAM 1512 unix 2 [ ] DGRAM 1504 unix 2 [ ] DGRAM 904 [root@wicca /root]# [download]	[reply] [d/l]