4 no strict 'refs'; # because users pass me bareword filehandles
5 our ($VERSION, @ISA, @EXPORT);
10 use Symbol qw(gensym qualify);
18 IPC::Open3, open3 - open a process for reading, writing, and error handling
22 $pid = open3(\*WTRFH, \*RDRFH, \*ERRFH,
23 'some cmd and args', 'optarg', ...);
26 $pid = open3($wtr, $rdr, $err,
27 'some cmd and args', 'optarg', ...);
31 Extremely similar to open2(), open3() spawns the given $cmd and
32 connects RDRFH for reading, WTRFH for writing, and ERRFH for errors. If
33 ERRFH is false, or the same file descriptor as RDRFH, then STDOUT and
34 STDERR of the child are on the same filehandle. The WTRFH will have
37 If WTRFH begins with C<< <& >>, then WTRFH will be closed in the parent, and
38 the child will read from it directly. If RDRFH or ERRFH begins with
39 C<< >& >>, then the child will send output directly to that filehandle.
40 In both cases, there will be a dup(2) instead of a pipe(2) made.
42 If either reader or writer is the null string, this will be replaced
43 by an autogenerated filehandle. If so, you must pass a valid lvalue
44 in the parameter slot so it can be overwritten in the caller, or
45 an exception will be raised.
47 open3() returns the process ID of the child process. It doesn't return on
48 failure: it just raises an exception matching C</^open3:/>. However,
49 C<exec> failures in the child are not detected. You'll have to
50 trap SIGPIPE yourself.
52 open3() does not wait for and reap the child process after it exits.
53 Except for short programs where it's acceptable to let the operating system
54 take care of this, you need to do this yourself. This is normally as
55 simple as calling C<waitpid $pid, 0> when you're done with the process.
56 Failing to do this can result in an accumulation of defunct or "zombie"
57 processes. See L<perlfunc/waitpid> for more information.
59 If you try to read from the child's stdout writer and their stderr
60 writer, you'll have problems with blocking, which means you'll want
61 to use select() or the IO::Select, which means you'd best use
62 sysread() instead of readline() for normal stuff.
64 This is very dangerous, as you may block forever. It assumes it's
65 going to talk to something like B<bc>, both writing to it and reading
66 from it. This is presumably safe because you "know" that commands
67 like B<bc> will read a line at a time and output a line at a time.
68 Programs like B<sort> that read their entire input stream first,
69 however, are quite apt to cause deadlock.
71 The big problem with this approach is that if you don't have control
72 over source code being run in the child process, you can't control
73 what it does with pipe buffering. Thus you can't just open a pipe to
74 C<cat -v> and continually read and write a line from it.
78 The order of arguments differs from that of open2().
82 # &open3: Marc Horowitz <marc@mit.edu>
83 # derived mostly from &open2 by tom christiansen, <tchrist@convex.com>
84 # fixed for 5.001 by Ulrich Kunitz <kunitz@mai-koeln.com>
85 # ported to Win32 by Ron Schmidt, Merrill Lynch almost ended my career
86 # fixed for autovivving FHs, tchrist again
88 # $Id: open3.pl,v 1.1 1993/11/23 06:26:15 marc Exp $
90 # usage: $pid = open3('wtr', 'rdr', 'err' 'some cmd and args', 'optarg', ...);
92 # spawn the given $cmd and connect rdr for
93 # reading, wtr for writing, and err for errors.
94 # if err is '', or the same as rdr, then stdout and
95 # stderr of the child are on the same fh. returns pid
96 # of child (or dies on failure).
99 # if wtr begins with '<&', then wtr will be closed in the parent, and
100 # the child will read from it directly. if rdr or err begins with
101 # '>&', then the child will send output directly to that fd. In both
102 # cases, there will be a dup() instead of a pipe() made.
105 # WARNING: this is dangerous, as you may block forever
106 # unless you are very careful.
108 # $wtr is left unbuffered.
111 # rdr or wtr are null
112 # a system call fails
114 our $Me = 'open3 (bug)'; # you should never see this, it's always localized
116 # Fatal.pm needs to be fixed WRT prototypes.
120 defined $pid or croak "$Me: fork failed: $!";
125 pipe $_[0], $_[1] or croak "$Me: pipe($_[0], $_[1]) failed: $!";
128 # I tried using a * prototype character for the filehandle but it still
129 # disallows a bearword while compiling under strict subs.
132 open $_[0], $_[1] or croak "$Me: open($_[0], $_[1]) failed: $!";
136 close $_[0] or croak "$Me: close($_[0]) failed: $!";
139 my $do_spawn = $^O eq 'os2' || $^O eq 'MSWin32';
143 my($package, $dad_wtr, $dad_rdr, $dad_err, @cmd) = @_;
144 my($dup_wtr, $dup_rdr, $dup_err, $kidpid);
146 # simulate autovivification of filehandles because
147 # it's too ugly to use @_ throughout to make perl do it for us
151 $dad_wtr = $_[1] = gensym unless defined $dad_wtr && length $dad_wtr;
152 $dad_rdr = $_[2] = gensym unless defined $dad_rdr && length $dad_rdr;
155 # must strip crud for croak to add back, or looks ugly
156 $@ =~ s/(?<=value attempted) at .*//s;
160 $dad_err ||= $dad_rdr;
162 $dup_wtr = ($dad_wtr =~ s/^[<>]&//);
163 $dup_rdr = ($dad_rdr =~ s/^[<>]&//);
164 $dup_err = ($dad_err =~ s/^[<>]&//);
166 # force unqualified filehandles into caller's package
167 $dad_wtr = qualify $dad_wtr, $package;
168 $dad_rdr = qualify $dad_rdr, $package;
169 $dad_err = qualify $dad_err, $package;
171 my $kid_rdr = gensym;
172 my $kid_wtr = gensym;
173 my $kid_err = gensym;
175 xpipe $kid_rdr, $dad_wtr if !$dup_wtr;
176 xpipe $dad_rdr, $kid_wtr if !$dup_rdr;
177 xpipe $dad_err, $kid_err if !$dup_err && $dad_err ne $dad_rdr;
179 $kidpid = $do_spawn ? -1 : xfork;
180 if ($kidpid == 0) { # Kid
181 # If she wants to dup the kid's stderr onto her stdout I need to
182 # save a copy of her stdout before I put something else there.
183 if ($dad_rdr ne $dad_err && $dup_err
184 && fileno($dad_err) == fileno(STDOUT)) {
186 xopen($tmp, ">&$dad_err");
191 xopen \*STDIN, "<&$dad_wtr" if fileno(STDIN) != fileno($dad_wtr);
194 xopen \*STDIN, "<&=" . fileno $kid_rdr;
197 xopen \*STDOUT, ">&$dad_rdr" if fileno(STDOUT) != fileno($dad_rdr);
200 xopen \*STDOUT, ">&=" . fileno $kid_wtr;
202 if ($dad_rdr ne $dad_err) {
204 # I have to use a fileno here because in this one case
205 # I'm doing a dup but the filehandle might be a reference
206 # (from the special case above).
207 xopen \*STDERR, ">&" . fileno $dad_err
208 if fileno(STDERR) != fileno($dad_err);
211 xopen \*STDERR, ">&=" . fileno $kid_err;
214 xopen \*STDERR, ">&STDOUT" if fileno(STDERR) != fileno(STDOUT);
217 exec @cmd # XXX: wrong process to croak from
218 or croak "$Me: exec of @cmd failed";
219 } elsif ($do_spawn) {
220 # All the bookkeeping of coincidence between handles is
221 # handled in spawn_with_handles.
225 $kid_rdr = \*{$dad_wtr};
226 push @close, $kid_rdr;
228 push @close, \*{$dad_wtr}, $kid_rdr;
231 $kid_wtr = \*{$dad_rdr};
232 push @close, $kid_wtr;
234 push @close, \*{$dad_rdr}, $kid_wtr;
236 if ($dad_rdr ne $dad_err) {
238 $kid_err = \*{$dad_err};
239 push @close, $kid_err;
241 push @close, \*{$dad_err}, $kid_err;
248 spawn_with_handles( [ { mode => 'r',
253 handle => \*STDOUT },
256 handle => \*STDERR },
262 xclose $kid_rdr if !$dup_wtr;
263 xclose $kid_wtr if !$dup_rdr;
264 xclose $kid_err if !$dup_err && $dad_rdr ne $dad_err;
265 # If the write handle is a dup give it away entirely, close my copy
267 xclose $dad_wtr if $dup_wtr;
269 select((select($dad_wtr), $| = 1)[0]); # unbuffer pipe
276 croak "open3(@_): not enough arguments";
278 return _open3 'open3', scalar caller, @_
281 sub spawn_with_handles {
282 my $fds = shift; # Fields: handle, mode, open_as
283 my $close_in_child = shift;
284 my ($fd, $pid, @saved_fh, $saved, %saved, @errs);
287 foreach $fd (@$fds) {
288 $fd->{tmp_copy} = IO::Handle->new_from_fd($fd->{handle}, $fd->{mode});
289 $saved{fileno $fd->{handle}} = $fd->{tmp_copy};
291 foreach $fd (@$fds) {
292 bless $fd->{handle}, 'IO::Handle'
293 unless eval { $fd->{handle}->isa('IO::Handle') } ;
294 # If some of handles to redirect-to coincide with handles to
295 # redirect, we need to use saved variants:
296 $fd->{handle}->fdopen($saved{fileno $fd->{open_as}} || $fd->{open_as},
299 unless ($^O eq 'MSWin32') {
300 # Stderr may be redirected below, so we save the err text:
301 foreach $fd (@$close_in_child) {
302 fcntl($fd, Fcntl::F_SETFD(), 1) or push @errs, "fcntl $fd: $!"
303 unless $saved{fileno $fd}; # Do not close what we redirect!
308 $pid = eval { system 1, @_ }; # 1 == P_NOWAIT
309 push @errs, "IO::Pipe: Can't spawn-NOWAIT: $!" if !$pid || $pid < 0;
312 foreach $fd (@$fds) {
313 $fd->{handle}->fdopen($fd->{tmp_copy}, $fd->{mode});
314 $fd->{tmp_copy}->close or croak "Can't close: $!";
316 croak join "\n", @errs if @errs;
320 1; # so require is happy