Hi guys,

I am writing a subroutine for daemonizing a process. Broadly speaking I've written it like this:

sub daemonize {
    # try to daemonize
    if (success) {
    return 1 
    } else {
    return errstr
    }
}
[download]

I call it this way

$isdaemon = daemonize()
if ($isdaemon ne "1") {
    print "error: $isdaemon";    
}
[download]

The problem with this is that the caller needs to do a "ne" check as it works for both 1 and error string. I would like to change the calling interface to:

if (! daemonize) {
    report error
}
[download]

But in the current implementation I can't use the desired way because if daemonize fails it returns an errstr which passes the "if (! daemonize)" test. I want to report the error, so I cannot return 0 on failure.

I wanted to set the errstr in a way that $! does it - which is make the subroutine call more intuitive, like the way we use open or close

open($fh, file) or die "$!";
[download]

The best I can do is this:

use Scalar::Util;
sub daemonize {
    # try to daemonize
    if (success) {
    return 1 
    } else {
    return dualvar 0, errstr
    }
}
[download]

so the usage is

$isdaemon = daemonize;
if ($isdaemon == 0) {
    print "error: $isdaemon";
}
[download]

which is better than the first way because I can use $isdaemon is both the string and numeric context and get my work done, but it still isn't as good as the way $! does it.

1. Is there a better way?
2. Can I not set $! and use my subroutines like I have used open() call above? A perl DBI module sets $DBI::err variable. I may do that but that's plan B.
3. How do you guys handle such situations where in the return value is more than success or error - like a subroutine which checks if lockfile is in use or not - return 0 if lockfile free, return pid if someone using the lockfile, return error if failed to check if someone is using it?

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