如何使用Perl检查Unix命令何时完成处理

Question

I am working on a capstone project and am hoping for some insight.

This is the first time I've worked with Perl and it's pretty much a basic Perl script to automate a few different Unix commands that need to be executed in a specific order. There are two lines throughout the script which executes a Unix command that needs to finish processing before it is acceptable for the rest of the script to run (data will be incorrect otherwise).

How am I able to use Perl (or maybe this is a Unix question?) to print a simple string once the Unix command has finished processing? I am looking into ways to read in the Unix command name but am not sure how to implement a way to check if the process is no longer running and to print a string such as "X command has finished processing" upon it's completion.

Example:

system("nohup scripts_pl/RunAll.pl &");

This runs a command in the background that takes time to process. I am asking how I can use Perl (or Unix?) to print a string once the process has finished.

Answer 1

I'm sorry if I didn't understand your asking context. But couldn't you use perl process fork function instead of & if you would like to do parallel process?

# parent process
if (my $pid = fork) {
    # this block behaves as a normal process

    system("nohup scripts_pl/RunAll2.pl"); # you can call other system (like RunAll2.pl)
    wait; # wait for the background processing
    say 'finished both';
}
# child process
else {
    # this block behaves as a background process
    system("nohup scripts_pl/RunAll.pl"); # trim &
}

Answer 2

You could try to use IPC::Open3 instead of system :

use IPC::Open3;
my $pid = open3("<&STDIN", ">&STDOUT", ">&STDERR", 'nohup scripts_pl/RunAll.pl');
waitpid( $pid, 0 );

Or, if you need to run nohup through the shell:

my $pid = open3("<&STDIN", ">&STDOUT", ">&STDERR", 'bash','-c', 'nohup scripts_pl/RunAll.pl & wait');

Update : Thanks to @ikegami. A better approach if you would like STDIN to stay open after running the command:

open(local *CHILD_STDIN, "<&", '/dev/null') or die $!;
my $pid = open3("<&CHILD_STDIN", ">&STDOUT", ">&STDERR", 'nohup scripts_pl/RunAll.pl');