Question

LINUX! In shell scripting if possible and show commands (please do not copy codes form others) Thank you!

Write a simple test program to find out PIDs of ALL ancestor (i.e., parent, grandparent ) processes of the current process or a given process specified by a PID. A parent process's PID of a given process pid can be found in /proc/$pid/status

Answer 1

pid is given as an argument, second is the pid of its parent, grandparent and so on.

use strict;
use warnings;
  
use Getoption::Long;
use Pod::Usage;
  
sub _usage_and_exit {
my %option = @_;
pod2usage(
-noperldoc => 1,
-verbose => 99,
-exitval => defined $option{help} && $option{help} ? 0 : 1,
-output => defined $option{help} && $option{help} ? \*STDOUT : \*STDERR,   
);
}
  
my %option;   
my $sw = Getoptionions( \%option, 'help|h', );   
my $pid = shift;

_usage_and_exit( help => $option{help} )
if not $sw   
or defined $option{help}
or not defined $pid
or $pid !~ /^\d+$/
or $pid < 1
or @ARGV;
  
while ( $pid > 0 ) {
open my $stat_fh, "<", "/proc/$pid/stat"
or die "no such pid: $pid\n";   
my $ppid = ( split /\s+/, <$stat_fh> )[3];
close $stat_fh;
print $pid, "\n";
$pid = $ppid;
}

This scripts non-zero value if it unable to find pid given or the process is in chain.