1IPC::Open3(3pm)        Perl Programmers Reference Guide        IPC::Open3(3pm)
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NAME

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

10           $pid = open3(\*CHLD_IN, \*CHLD_OUT, \*CHLD_ERR,
11                           'some cmd and args', 'optarg', ...);
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13           my($wtr, $rdr, $err);
14           use Symbol 'gensym'; $err = gensym;
15           $pid = open3($wtr, $rdr, $err,
16                           'some cmd and args', 'optarg', ...);
17
18           waitpid( $pid, 0 );
19           my $child_exit_status = $? >> 8;
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DESCRIPTION

22       Extremely similar to open2(), open3() spawns the given $cmd and
23       connects CHLD_OUT for reading from the child, CHLD_IN for writing to
24       the child, and CHLD_ERR for errors.  If CHLD_ERR is false, or the same
25       file descriptor as CHLD_OUT, then STDOUT and STDERR of the child are on
26       the same filehandle (this means that an autovivified lexical cannot be
27       used for the STDERR filehandle, see SYNOPSIS).  The CHLD_IN will have
28       autoflush turned on.
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30       If CHLD_IN begins with "<&", then CHLD_IN will be closed in the parent,
31       and the child will read from it directly.  If CHLD_OUT or CHLD_ERR
32       begins with ">&", then the child will send output directly to that
33       filehandle.  In both cases, there will be a dup(2) instead of a pipe(2)
34       made.
35
36       If either reader or writer is the null string, this will be replaced by
37       an autogenerated filehandle.  If so, you must pass a valid lvalue in
38       the parameter slot so it can be overwritten in the caller, or an
39       exception will be raised.
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41       The filehandles may also be integers, in which case they are understood
42       as file descriptors.
43
44       open3() returns the process ID of the child process.  It doesn't return
45       on failure: it just raises an exception matching "/^open3:/".  However,
46       "exec" failures in the child (such as no such file or permission
47       denied), are just reported to CHLD_ERR under Windows and OS/2, as it is
48       not possible to trap them.
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50       If the child process dies for any reason, the next write to CHLD_IN is
51       likely to generate a SIGPIPE in the parent, which is fatal by default.
52       So you may wish to handle this signal.
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54       Note if you specify "-" as the command, in an analogous fashion to
55       "open(FOO, "-|")" the child process will just be the forked Perl
56       process rather than an external command.  This feature isn't yet
57       supported on Win32 platforms.
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59       open3() does not wait for and reap the child process after it exits.
60       Except for short programs where it's acceptable to let the operating
61       system take care of this, you need to do this yourself.  This is
62       normally as simple as calling "waitpid $pid, 0" when you're done with
63       the process.  Failing to do this can result in an accumulation of
64       defunct or "zombie" processes.  See "waitpid" in perlfunc for more
65       information.
66
67       If you try to read from the child's stdout writer and their stderr
68       writer, you'll have problems with blocking, which means you'll want to
69       use select() or the IO::Select, which means you'd best use sysread()
70       instead of readline() for normal stuff.
71
72       This is very dangerous, as you may block forever.  It assumes it's
73       going to talk to something like bc, both writing to it and reading from
74       it.  This is presumably safe because you "know" that commands like bc
75       will read a line at a time and output a line at a time.  Programs like
76       sort that read their entire input stream first, however, are quite apt
77       to cause deadlock.
78
79       The big problem with this approach is that if you don't have control
80       over source code being run in the child process, you can't control what
81       it does with pipe buffering.  Thus you can't just open a pipe to "cat
82       -v" and continually read and write a line from it.
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See Also

85       IPC::Open2
86           Like Open3 but without STDERR capture.
87
88       IPC::Run
89           This is a CPAN module that has better error handling and more
90           facilities than Open3.
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WARNING

93       The order of arguments differs from that of open2().
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97perl v5.30.2                      2020-03-27                   IPC::Open3(3pm)
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