IPC::Open3 - phpMan

NAME
    IPC::Open3 - open a process for reading, writing, and error handling
    using open3()

SYNOPSIS
        use Symbol 'gensym'; # vivify a separate handle for STDERR
        my $pid = open3(my $chld_in, my $chld_out, my $chld_err = gensym,
                        'some', 'cmd', 'and', 'args');
        # or pass the command through the shell
        my $pid = open3(my $chld_in, my $chld_out, my $chld_err = gensym,
                        'some cmd and args');

        # read from parent STDIN
        # send STDOUT and STDERR to already open handle
        open my $outfile, '>>', 'output.txt' or die "open failed: $!";
        my $pid = open3('<&STDIN', $outfile, undef,
                        'some', 'cmd', 'and', 'args');

        # write to parent STDOUT and STDERR
        my $pid = open3(my $chld_in, '>&STDOUT', '>&STDERR',
                        'some', 'cmd', 'and', 'args');

        # reap zombie and retrieve exit status
        waitpid( $pid, 0 );
        my $child_exit_status = $? >> 8;

DESCRIPTION
    Extremely similar to open2(), open3() spawns the given command and
    connects $chld_out for reading from the child, $chld_in for writing to
    the child, and $chld_err for errors. If $chld_err is false, or the same
    file descriptor as $chld_out, then STDOUT and STDERR of the child are on
    the same filehandle. This means that an autovivified lexical cannot be
    used for the STDERR filehandle, but gensym from Symbol can be used to
    vivify a new glob reference, see "SYNOPSIS". The $chld_in will have
    autoflush turned on.

    If $chld_in begins with "<&", then $chld_in will be closed in the
    parent, and the child will read from it directly. If $chld_out or
    $chld_err begins with ">&", then the child will send output directly to
    that filehandle. In both cases, there will be a dup(2) instead of a
    pipe(2) made.

    If either reader or writer is the empty string or undefined, this will
    be replaced by an autogenerated filehandle. If so, you must pass a valid
    lvalue in the parameter slot so it can be overwritten in the caller, or
    an exception will be raised.

    The filehandles may also be integers, in which case they are understood
    as file descriptors.

    open3() returns the process ID of the child process. It doesn't return
    on failure: it just raises an exception matching "/^open3:/". However,
    "exec" failures in the child (such as no such file or permission
    denied), are just reported to $chld_err under Windows and OS/2, as it is
    not possible to trap them.

    If the child process dies for any reason, the next write to $chld_in is
    likely to generate a SIGPIPE in the parent, which is fatal by default.
    So you may wish to handle this signal.

    Note if you specify "-" as the command, in an analogous fashion to
    "open(my $fh, "-|")" the child process will just be the forked Perl
    process rather than an external command. This feature isn't yet
    supported on Win32 platforms.

    open3() does not wait for and reap the child process after it exits.
    Except for short programs where it's acceptable to let the operating
    system take care of this, you need to do this yourself. This is normally
    as simple as calling "waitpid $pid, 0" when you're done with the
    process. Failing to do this can result in an accumulation of defunct or
    "zombie" processes. See "waitpid" in perlfunc for more information.

    If you try to read from the child's stdout writer and their stderr
    writer, you'll have problems with blocking, which means you'll want to
    use select() or IO::Select, which means you'd best use sysread() instead
    of readline() for normal stuff.

    This is very dangerous, as you may block forever. It assumes it's going
    to talk to something like bc(1), both writing to it and reading from it.
    This is presumably safe because you "know" that commands like bc(1) will
    read a line at a time and output a line at a time. Programs like sort(1)
    that read their entire input stream first, however, are quite apt to
    cause deadlock.

    The big problem with this approach is that if you don't have control
    over source code being run in the child process, you can't control what
    it does with pipe buffering. Thus you can't just open a pipe to "cat -v"
    and continually read and write a line from it.

See Also
    IPC::Open2
        Like Open3 but without STDERR capture.

    IPC::Run
        This is a CPAN module that has better error handling and more
        facilities than Open3.

WARNING
    The order of arguments differs from that of open2().