How can I check the status of the first program in pipeline in Perl's system()?

Question

perl -e \'system (\"crontab1 -l\");print $?\'

returns -1 as expected (program crontab1 doesn\'t exist)

perl -e \'system (\"crontab1 -l|         


        

Answer 1

[This was composed as an answer to another question which was closed as a duplicate of this one.]

Executing a shell command requires executing a shell. To that end,

system($shell_command)

is equivalent to

system('/bin/sh', '-c', $shell_command)

As such, all of your examples run a single program (/bin/sh). If you want the exit statuses of multiple children, you're going to need to have multiple children!

use IPC::Open3 qw( open3 );

open(local *CHILD1_STDIN, '<', '/dev/null')
   or die $!;

pipe(local *CHILD2_STDIN, local *CHILD1_STDOUT)
   or die $!;

my $child1_pid = open3(
   '<&CHILD1_STDIN',
   '>&CHILD1_STDOUT',
   '>&STDERR',
   'prog1', 'arg1', 'arg2',
);

my $child2_pid = open3(
   '<&CHILD2_STDIN',
   '>&STDOUT',
   '>&STDERR',
   'prog2', 'arg1', 'arg2',
);

my @pipe_status = map { waitpid($_, 0) } $child1_pid, $child2_pid;

IPC::Open3 is rather low level. IPC::Run3 and/or IPC::Run can possibly make this easier. [Update: Indeed, IPC::Run does].