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26 Feb 2001 18:57:38 +0100
Gnus/5.0808 (Gnus v5.8.8) XEmacs/21.1 (Cuyahoga Valley)
Pavel Roskin <address@hidden> writes:
> Hello, Akim!
> I'm not a Perl guru, and maybe I don't quite understand you doubts, but
> I'll try to anser the questions that I can answer.
> > Yep, I know this, but the documentation for die was saying it should
> > be automatic. And in fact, it is automatic: it works fine when -d is
> > given, i.e., when END does not run unlink.
> You are missing one important point.
> > die LIST
> > Outside an `eval', prints the value of LIST to
> > `STDERR' and exits with the current value of `$!'
> > (errno). If `$!' is `0', exits with the value of
> If `$!' is `0'!!! This is not the case if system() fails. In this case the
> exit status is in the upper byte of $!,
This is not my reading :(
system PROGRAM LIST
Does exactly the same thing as `exec LIST', except
that a fork is done first, and the parent process
waits for the child process to complete. Note
that argument processing varies depending on the
number of arguments. If there is more than one
argument in LIST, or if LIST is an array with more
than one value, starts the program given by the
first element of the list with arguments given by
the rest of the list. If there is only one scalar
argument, the argument is checked for shell
metacharacters, and if there are any, the entire
argument is passed to the system's command shell
for parsing (this is `/bin/sh -c' on Unix plat
forms, but varies on other platforms). If there
are no shell metacharacters in the argument, it is
split into words and passed directly to `execvp',
which is more efficient.
Beginning with v5.6.0, Perl will attempt to flush
all files opened for output before any operation
that may do a fork, but this may not be supported
on some platforms (see the perlport manpage). To
be safe, you may need to set `$|' ($AUTOFLUSH in
English) or call the `autoflush()' method of
`IO::Handle' on any open handles.
The return value is the exit status of the program
as returned by the `wait' call. To get the actual
exit value divide by 256. See also the exec entry
elsewhere in this document. This is not what you
want to use to capture the output from a command,
for that you should use merely backticks or
`qx//', as described in the section on "`STRING`"
in the perlop manpage. Return value of -1 indi
This is not => cates a failure to start the program (inspect $!
our case => for the reason).
Like `exec', `system' allows you to lie to a pro
gram about its name if you use the `system PROGRAM
LIST' syntax. Again, see the exec entry elsewhere
in this document.
Because `system' and backticks block `SIGINT' and
`SIGQUIT', killing the program they're running
doesn't actually interrupt your program.
@args = ("command", "arg1", "arg2");
system(@args) == 0
or die "system @args failed: $?"
This is => You can check all the failure possibilities by
what I => inspecting `$?' like this:
meant to use.
This is not $!. $exit_value = $? >> 8;
$signal_num = $? & 127;
$dumped_core = $? & 128;
When the arguments get executed via the system
shell, results and return codes will be subject to
its quirks and capabilities. See the section on
"`STRING`" in the perlop manpage and the exec
entry elsewhere in this document for details.