What exactly are you having problems with? This is quite well documented in system's documentation.

my $rv = system('perl -e "exit(123)"');

die("Unable to launch command: $!\n")
   if $rv == -1;

die("Child died with signal ", ($rv & 127), "\n")
   if $rv & 127;

die("Child exited with value ", ($rv >> 8), "\n")
   if $rv >> 8;

print("Child exited successfully\n");
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outputs

Child exited with value 123
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Keep in mind that system("$cmd; echo $status"); will return the error code of the shell used to launch these two commands, which will be the error code of echo if nothing goes wrong.