Antw: Re: [] pipe or die

Roland Bauer Roland.Bauer at
Mon May 15 03:05:55 CDT 2000

* * * vienna-pm-list * * *

> Johannes Fuernkranz wrote on Thu, May 04 2000 (13:40:18 +0200):
> > open(IN,"non_existent_script |") or die "Script doesn't exist";

Ergaenzug aus dem Perl-FAQ ;-)

Why doesn't open() return an error when a pipe open fails?

    It does, but probably not how you expect it to. On systems that
    follow the standard fork()/exec() paradigm (such as Unix), it works
    like this: open() causes a fork(). In the parent, open() returns
    with the process ID of the child. The child exec()s the command to
    be piped to/from. The parent can't know whether the exec() was
    successful or not - all it can return is whether the fork()
    succeeded or not. To find out if the command succeeded, you have to
    catch SIGCHLD and wait() to get the exit status. You should also
    catch SIGPIPE if you're writing to the child -- you may not have
    found out the exec() failed by the time you write. This is
    documented in the perlipc manpage.

    On systems that follow the spawn() paradigm, open() *might* do what
    you expect - unless perl uses a shell to start your command. In
    this case the fork()/exec() description still applies.

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