[perl] How can I store the result of a system command in a Perl variable?

$ cat test.pl
my $pid = 5892;
my $not = system("top -H -p $pid -n 1 | grep myprocess | wc -l");
print "not = $not\n";
$ perl test.pl
11
not = 0
$

I want to capture the result i.e. 11 into a variable. How can I do that?

Also for eg. you can use IPC::Run:

use IPC::Run qw(run);

my $pid = 5892;
run [qw(top -H -n 1 -p), $pid],
    '|', sub { print grep { /myprocess/ } <STDIN> },
    '|', [qw(wc -l)],
    '>', \my $out;

print $out;

• processes are running without bash subprocess
• can be piped to perl subs
• very similar to shell

Use backticks for system commands, which helps to store their results into Perl variables.

my $pid = 5892;
my $not = ``top -H -p $pid -n 1 | grep myprocess | wc -l`; 
print "not = $not\n";

The easiest way is to use the `` feature in Perl. This will execute what is inside and return what was printed to stdout:

 my $pid = 5892;
 my $var = `top -H -p $pid -n 1 | grep myprocess | wc -l`;
 print "not = $var\n";

This should do it.

Try using qx{command} rather than backticks. To me, it's a bit better because: you can do SQL with it and not worry about escaping quotes and such. Depending on the editor and screen, my old eyes tend to miss the tiny back ticks, and it shouldn't ever have an issue with being overloaded like using angle brackets versus glob.

Using backtick or qx helps, thanks everybody for the answers. However, I found that if you use backtick or qx, the output contains trailing newline and I need to remove that. So I used chomp.

chomp($host = `hostname`);
chomp($domain = `domainname`);
$fqdn = $host.".".$domain;

More information here: http://irouble.blogspot.in/2011/04/perl-chomp-backticks.html