I ran into an oddity determining the success of a tar process using it's exit code. In the following code $result evaluates to 0, even though /nonexistent doesn't exist and tar is unable to open the output file (tested under Ubuntu and CentOS):

my $pid = open(CMD, '-|');

die("cannot fork: $!") unless (defined $pid);

if ($pid == 0) {
    close(STDERR);
    open(STDERR, ">&STDOUT")
        or print "Unable to reopen STDOUT, errors may be lost: $!";
    exec('/bin/tar', 'czf', '/nonexistent/test.tar.gz', '.')
        or die("Unable to exec: $!")
}

local $/ = undef;
my $output .= <CMD>;

close (CMD);
my $result = $? >> 8;

print "result = $result\n";
print $output;

[download]
Output: 
result = 0
/bin/tar: /nonexistent/test.tar.gz: Cannot open: No such file or direc
+tory
/bin/tar: Error is not recoverable: exiting now

[download]

When I remove the 'z' flag from tar result correctly evaluates to a non zero exist status.

Bash returns the expected result when you run this as /bin/tar czf /nonexistent/test.tar.gz .; echo $?, but I have not been able to obtain the same result (testing for the successful completion of the archive task) in Perl.

I think the key difference here is that with the 'z' flag tar forks, opens the output file and execs gzip, but the pipe is only connected to tar not the child process.

In reply to Exit codes from forking children by DustinLundquist

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