return values with system()

jason has asked for the wisdom of the Perl Monks concerning the following question:

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Re: return values with system() by davorg (Chancellor) on Feb 13, 2007 at 16:56 UTC
perldoc system The return value is the exit status of the program as returned by the "wait" call. To get the actual exit value, shift right by eight (see below). Or maybe you want the $? variable (see perldoc perlvar for details). -- <http://dave.org.uk> "The first rule of Perl club is you do not talk about Perl club." -- Chip Salzenberg	[reply]
Re: return values with system() by Joost (Canon) on Feb 13, 2007 at 17:06 UTC
When I run the application locally it sets the environment variable $status to 4. .... system($cmd;echo $status); Have you tried that? AFAIK you can't "push" environment variables to the parent process (in this case the shell) on UNIX - i.e. if you set an env variable it will only affect the current process and it's children. I would probably just print out the value to STDOUT and retrieve it in the perl process using backquotes. Setting variables and then echo()ing them is useless overhead. my $output = `some-program`; print "Output from some-program is '$output'"; [download] that way you're much more flexible and it's easier to debug since you can immediately see the output if you run the program on its own. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l]
Re^2: return values with system() by jason (Initiate) on Feb 13, 2007 at 19:03 UTC
Thanks. This is what I'll do.	[reply]
Re: return values with system() by ikegami (Patriarch) on Feb 13, 2007 at 18:21 UTC
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 $rv >> 8; print("Child exited successfully\n");` [download] outputs `Child exited with value 123` [download] Keep in mind that `system("$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.	[reply] [d/l] [select]
Re: return values with system() by sauoq (Abbot) on Feb 13, 2007 at 18:41 UTC
When I run the application locally it sets the environment variable $status to 4. Oh? How do you run it? Do you source it? Eval it? Are you on unix or a unix-like OS? If what you claim is true, you should theoretically be able to `system("$cmd; exit \$status")` but your command should not be able to affect its parent's shell. Oh, wait... do you use csh tcsh or something?... that would explain $status. (I'm bourne-shell-centric, I guess.) `-sauoq "My two cents aren't worth a dime.";`	[reply] [d/l]