$ 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?
-
1Also see What's the differences between system and backticks and pipes in Perl?jww– jww2016-06-29 02:16:39 +00:00Commented Jun 29, 2016 at 2:16
Add a comment
|
6 Answers
From Perlfaq8:
You're confusing the purpose of system() and backticks (``). system() runs a command and returns exit status information (as a 16 bit value: the low 7 bits are the signal the process died from, if any, and the high 8 bits are the actual exit value). Backticks (``) run a command and return what it sent to STDOUT.
$exit_status = system("mail-users");
$output_string = `ls`;
There are many ways to execute external commands from Perl. The most commons with their meanings are:
1 Comment
Hi-Angel
Worth noting: if you want the output to be split on newlines (which is probably the case in the example with with
ls), just assign it to "array" variable. I.e. replace $output_string = `ls` with @output_string = `ls`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.
2 Comments
Lazer
Is the $pid substitution within backtics a new feature? Can't get it to work with
v5.6.1.
Peter Tillemans
This has worked as far as I can remember. e.g. try :
perl -e '$a="Hello"; print `echo $a`'Try using qx{command} rather than backticks. To me, it's a bit better because: you can do SQL with it and not worry about escaping quotes and such. Depending on the editor and screen, my old eyes tend to miss the tiny back ticks, and it shouldn't ever have an issue with being overloaded like using angle brackets versus glob.
1 Comment
Alexey
Great answer! Solved my problem!
Using backtick or qx helps, thanks everybody for the answers. However, I found that if you use backtick or qx, the output contains trailing newline and I need to remove that. So I used chomp.
chomp($host = `hostname`);
chomp($domain = `domainname`);
$fqdn = $host.".".$domain;
More information here: http://irouble.blogspot.in/2011/04/perl-chomp-backticks.html
2 Comments
Martin T.
chomp really is a strange beast... i don't get it, why $host =
hostname ; $out = chomp($host) is not working...
brian d foy
chomp returns the number of characters it removed after it modifies your argument. You almost never care about what chomp returns.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";
Comments
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
