in reply to system commands/shell and perl variables.

With a command as complex as you showed, I would very much recommend doing as much of it in Perl as possible instead of shelling out - there are potential security issues, quoting challenges, etc. with shelling out. I wrote about that at length here (with code examples). In particular, both fgrep and awk can be replaced by pure Perl. Instead of ps, you might try Proc::ProcessTable. That leaves only xl and sockstat. If you want to run those external processes and need to feed something to their STDIN, I'd recommend IPC::Run3. Otherwise, if you just want a simple replacement for backticks, there's capturex from IPC::System::Simple.

Replies are listed 'Best First'.
Re^2: system commands/shell and perl variables.
by knight.neo (Initiate) on Jan 22, 2019 at 17:34 UTC
    Hi there, First of all thank you very much. I am starting with perl and I trying to automate my shell scripts by perl scripts. Here my final script ( of course I will follow HAUKEX advice which is what I want. 
    
#!/usr/local/bin/perl
use strict;
use warnings;

my @get_vmlist = ( `xl list` );

sub show_vmlist {
        print @get_vmlist;
}


my $arg =  shift @ARGV;
my $vm_run = pop @ARGV;

sub get_vncport {
        my $DOMID = qq(DOM_ID="`xl list | fgrep $vm_run | awk '{print 
+\$2}'`" && VNCPORT="`ps x | fgrep -m 1 "domid \$DOM_ID" | awk '{print
+ \$1}'`" && sockstat -4l | fgrep \$VNCPORT | awk '{print \$6}');
        print `$DOMID`;
}

my %rec_args = ( vmlist => \&show_vmlist,
        getvnc => \&get_vncport,
);

if (defined $arg && exists $rec_args{$arg}) {
        $rec_args{$arg}->();
}

    [download]
[reply]
[d/l]
[reply]
[d/l]
[select]
        Hi haukex, Absolutely , xl is part of xen-tools. xl is used to manipulate virtual machines as other system parameters as well. Here is a tipical output of "xl list" ( used to list running virtual machines ) I am using FreeBSD as dom0. When I start a VM on HVM mode, I use VNC to access vm console. 
        # xl list
Name                                        ID   Mem VCPUs      State 
+  Time(s)
Domain-0                                     0 18442     2     r----- 
+  16256.2
git                                          1  1023     2     -b---- 
+  14499.4
zabbix                                       2   512     1     -b---- 
+   3228.6
jenkins                                      3  4096     2     -b---- 
+  21733.3
openbsd                                      4  2048     1     -b---- 
+   1202.6
wiki                                         5  2048     1     -b---- 
+   1140.4
builder                                      6  4096     2     -b---- 
+    206.9

        [download]
        This perl script which you guys helped, do the follow: "pxl vmlist" ( which will return xl list ), and "pxl getvnc jenkins" ( which will return vnc port listening of that VM ) "127.0.0.1:5906" Next steps, I will provide ssh port forward and connect to it :) Thanks again
[reply]
[d/l]

In Section Seekers of Perl Wisdom