CODEWITHSUNDEEP
linuxperlbashpid
Jordan Doyle
Jordan Doyle

Reputation: 3026

Perl not returning PID

If I run the command

nohup ./run > /dev/null 2>&1 & disown

in my terminal I get back something along the lines of [1] 1234 which I understand to be the PID.

However, when I run the following in Perl, it returns an error about disown not being defined or something, but that's not the point. When I remove disown, the terminal returns the same thing but Perl returns nothing. The variable it was assigned to is just blank.

my $command = `nohup ./run > /dev/null 2>&1 &`;
print("a " . $command); // "a " to check if it's actually printing anything.

Output:

a

Expected output:

[1] 1234

How do I get Perl to display the PID of the command which I can then parse with

@ar  = split(/\s+/, $process);
$pid = $ar[1];

Which was provided by another Stackoverflow user in my previous question.

Upvotes: 3

Views: 305

Answers (2)

michael501
michael501

Reputation: 1482

try this 

  $pin1=`(nohup ./run >/dev/null 2>&1 \& echo \$! )`

Upvotes: 0

ikegami
ikegami

Reputation: 385655

[1] 1234 is only output by bash for interactive shells (i.e. one started with the -i option).

my $command = `sh -ic 'nohup ./run > /dev/null 2>&1 &' 2>&1`;
die "Can't execute child: $!\n"                if $? < 0;
die "Child killed by signal ".($? & 0x7F)."\n" if $? & 0x7F;
die "Child exited with error ".($? >> 8)."\n"  if $? >> 8;

or better yet,

use IPC::System::Simple qw( capture );
capture(q{sh -ic 'nohup ./run > /dev/null 2>&1 &' 2>&1});

Another option is to "daemonize" using Daemon::Daemonize. Unfortunately, it only returns the PID via a pid file.

Upvotes: 8

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