| 1 | package IPC::Open2; |
| 2 | |
| 3 | use strict; |
| 4 | our ($VERSION, @ISA, @EXPORT); |
| 5 | |
| 6 | require 5.000; |
| 7 | require Exporter; |
| 8 | |
| 9 | $VERSION = 1.01; |
| 10 | @ISA = qw(Exporter); |
| 11 | @EXPORT = qw(open2); |
| 12 | |
| 13 | =head1 NAME |
| 14 | |
| 15 | IPC::Open2, open2 - open a process for both reading and writing |
| 16 | |
| 17 | =head1 SYNOPSIS |
| 18 | |
| 19 | use IPC::Open2; |
| 20 | |
| 21 | $pid = open2(\*RDRFH, \*WTRFH, 'some cmd and args'); |
| 22 | # or without using the shell |
| 23 | $pid = open2(\*RDRFH, \*WTRFH, 'some', 'cmd', 'and', 'args'); |
| 24 | |
| 25 | # or with handle autovivification |
| 26 | my($rdrfh, $wtrfh); |
| 27 | $pid = open2($rdrfh, $wtrfh, 'some cmd and args'); |
| 28 | # or without using the shell |
| 29 | $pid = open2($rdrfh, $wtrfh, 'some', 'cmd', 'and', 'args'); |
| 30 | |
| 31 | =head1 DESCRIPTION |
| 32 | |
| 33 | The open2() function runs the given $cmd and connects $rdrfh for |
| 34 | reading and $wtrfh for writing. It's what you think should work |
| 35 | when you try |
| 36 | |
| 37 | $pid = open(HANDLE, "|cmd args|"); |
| 38 | |
| 39 | The write filehandle will have autoflush turned on. |
| 40 | |
| 41 | If $rdrfh is a string (that is, a bareword filehandle rather than a glob |
| 42 | or a reference) and it begins with C<< >& >>, then the child will send output |
| 43 | directly to that file handle. If $wtrfh is a string that begins with |
| 44 | C<< <& >>, then $wtrfh will be closed in the parent, and the child will read |
| 45 | from it directly. In both cases, there will be a dup(2) instead of a |
| 46 | pipe(2) made. |
| 47 | |
| 48 | If either reader or writer is the null string, this will be replaced |
| 49 | by an autogenerated filehandle. If so, you must pass a valid lvalue |
| 50 | in the parameter slot so it can be overwritten in the caller, or |
| 51 | an exception will be raised. |
| 52 | |
| 53 | open2() returns the process ID of the child process. It doesn't return on |
| 54 | failure: it just raises an exception matching C</^open2:/>. However, |
| 55 | C<exec> failures in the child are not detected. You'll have to |
| 56 | trap SIGPIPE yourself. |
| 57 | |
| 58 | open2() does not wait for and reap the child process after it exits. |
| 59 | Except for short programs where it's acceptable to let the operating system |
| 60 | take care of this, you need to do this yourself. This is normally as |
| 61 | simple as calling C<waitpid $pid, 0> when you're done with the process. |
| 62 | Failing to do this can result in an accumulation of defunct or "zombie" |
| 63 | processes. See L<perlfunc/waitpid> for more information. |
| 64 | |
| 65 | This whole affair is quite dangerous, as you may block forever. It |
| 66 | assumes it's going to talk to something like B<bc>, both writing |
| 67 | to it and reading from it. This is presumably safe because you |
| 68 | "know" that commands like B<bc> will read a line at a time and |
| 69 | output a line at a time. Programs like B<sort> that read their |
| 70 | entire input stream first, however, are quite apt to cause deadlock. |
| 71 | |
| 72 | The big problem with this approach is that if you don't have control |
| 73 | over source code being run in the child process, you can't control |
| 74 | what it does with pipe buffering. Thus you can't just open a pipe to |
| 75 | C<cat -v> and continually read and write a line from it. |
| 76 | |
| 77 | The IO::Pty and Expect modules from CPAN can help with this, as they |
| 78 | provide a real tty (well, a pseudo-tty, actually), which gets you |
| 79 | back to line buffering in the invoked command again. |
| 80 | |
| 81 | =head1 WARNING |
| 82 | |
| 83 | The order of arguments differs from that of open3(). |
| 84 | |
| 85 | =head1 SEE ALSO |
| 86 | |
| 87 | See L<IPC::Open3> for an alternative that handles STDERR as well. This |
| 88 | function is really just a wrapper around open3(). |
| 89 | |
| 90 | =cut |
| 91 | |
| 92 | # &open2: tom christiansen, <tchrist@convex.com> |
| 93 | # |
| 94 | # usage: $pid = open2('rdr', 'wtr', 'some cmd and args'); |
| 95 | # or $pid = open2('rdr', 'wtr', 'some', 'cmd', 'and', 'args'); |
| 96 | # |
| 97 | # spawn the given $cmd and connect $rdr for |
| 98 | # reading and $wtr for writing. return pid |
| 99 | # of child, or 0 on failure. |
| 100 | # |
| 101 | # WARNING: this is dangerous, as you may block forever |
| 102 | # unless you are very careful. |
| 103 | # |
| 104 | # $wtr is left unbuffered. |
| 105 | # |
| 106 | # abort program if |
| 107 | # rdr or wtr are null |
| 108 | # a system call fails |
| 109 | |
| 110 | require IPC::Open3; |
| 111 | |
| 112 | sub open2 { |
| 113 | local $Carp::CarpLevel = $Carp::CarpLevel + 1; |
| 114 | return IPC::Open3::_open3('open2', scalar caller, |
| 115 | $_[1], $_[0], '>&STDERR', @_[2 .. $#_]); |
| 116 | } |
| 117 | |
| 118 | 1 |