Unable to inspect variable - perl

Question

I'm having a very difficult time inspecting the $return variable. The print "return = ". $return ."\n"; always comes back blank even though the process is still running. I do receive a warning about uninitialized variable. Can someone please explain?
my $process="MInstaller";
my $return=` ps -eaf |grep $process | grep -v grep`;
sub chk_proc{
print "in chk_proc\n";
print "\n";
print "return = ". $return ."\n";
while ( my $return ne "" ) {
sleep(5);
};
};

Answer 1

You're close. Your code doesn't works, because the variable $return in the
while ( my $return ne "" ) {
is another variable (declared in the scope of while) as your first $return.
You can try the next:
use 5.014;
use warnings;
chk_proc('[M]Installer'); #use the [] trick to avoid the 'grep -v grep :)
sub chk_proc{ while( qx(ps -eaf |grep $_[0]) ) {sleep 5} };

Answer 2

Are you using use warnings; and use strict;?
What about using pgrep instead of ps?
What happens if $return returns more than one line?
Your program would flow better if your subroutine merely checked to see if the process is running and you used that in another loop.
Here, my check process subroutine returns a list of all the processes it find. I can use this in my loop to see if the process itself has stopped. I could have used qx() to get a process list, then use split to create a list of processes.
use warnings;
use strict;
use feature qw(say);
use constant {
PROCESS => "MInstaller",
SLEEP => 5,
};
while ( process_check( PROCESS ) ) {
say qq(Process ) . PROCESS . qq( is running...);
sleep SLEEP;;
}
say qq(Process ) . PROCESS . qq( has ended.);
sub process_check {
my $process = shift;
open ( my $process_fh, "-|", "pgrep $process" );
my #process_list;
while ( my $line = <$process_fh> ) {
chomp $line;
push #process_list, $line;
}
close $process_fh;
return #process_list;
}