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 The filehandles may also be integers, in which case they are understood
50 open3() returns the process ID of the child process. It doesn't return on
51 failure: it just raises an exception matching C</^open3:/>. However,
52 C<exec> failures in the child are not detected. You'll have to
53 trap SIGPIPE yourself.
55 Note if you specify C<-> as the command, in an analogous fashion to
56 C<open(FOO, "-|")> the child process will just be the forked Perl
57 process rather than an external command. This feature isn't yet
58 supported on Win32 platforms.
60 open3() does not wait for and reap the child process after it exits.
61 Except for short programs where it's acceptable to let the operating system
62 take care of this, you need to do this yourself. This is normally as
63 simple as calling C<waitpid $pid, 0> when you're done with the process.
64 Failing to do this can result in an accumulation of defunct or "zombie"
65 processes. See L<perlfunc/waitpid> for more information.
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
69 to use select() or the IO::Select, which means you'd best use
70 sysread() instead of readline() for normal stuff.
72 This is very dangerous, as you may block forever. It assumes it's
73 going to talk to something like B<bc>, both writing to it and reading
74 from it. This is presumably safe because you "know" that commands
75 like B<bc> will read a line at a time and output a line at a time.
76 Programs like B<sort> that read their entire input stream first,
77 however, are quite apt to cause deadlock.
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
81 what it does with pipe buffering. Thus you can't just open a pipe to
82 C<cat -v> and continually read and write a line from it.
86 The order of arguments differs from that of open2().
90 # &open3: Marc Horowitz <marc@mit.edu>
91 # derived mostly from &open2 by tom christiansen, <tchrist@convex.com>
92 # fixed for 5.001 by Ulrich Kunitz <kunitz@mai-koeln.com>
93 # ported to Win32 by Ron Schmidt, Merrill Lynch almost ended my career
94 # fixed for autovivving FHs, tchrist again
95 # allow fd numbers to be used, by Frank Tobin
96 # allow '-' as command (c.f. open "-|"), by Adam Spiers <perl@adamspiers.org>
98 # $Id: open3.pl,v 1.1 1993/11/23 06:26:15 marc Exp $
100 # usage: $pid = open3('wtr', 'rdr', 'err' 'some cmd and args', 'optarg', ...);
102 # spawn the given $cmd and connect rdr for
103 # reading, wtr for writing, and err for errors.
104 # if err is '', or the same as rdr, then stdout and
105 # stderr of the child are on the same fh. returns pid
106 # of child (or dies on failure).
109 # if wtr begins with '<&', then wtr will be closed in the parent, and
110 # the child will read from it directly. if rdr or err begins with
111 # '>&', then the child will send output directly to that fd. In both
112 # cases, there will be a dup() instead of a pipe() made.
115 # WARNING: this is dangerous, as you may block forever
116 # unless you are very careful.
118 # $wtr is left unbuffered.
121 # rdr or wtr are null
122 # a system call fails
124 our $Me = 'open3 (bug)'; # you should never see this, it's always localized
126 # Fatal.pm needs to be fixed WRT prototypes.
130 defined $pid or croak "$Me: fork failed: $!";
135 pipe $_[0], $_[1] or croak "$Me: pipe($_[0], $_[1]) failed: $!";
138 # I tried using a * prototype character for the filehandle but it still
139 # disallows a bearword while compiling under strict subs.
142 open $_[0], $_[1] or croak "$Me: open($_[0], $_[1]) failed: $!";
146 close $_[0] or croak "$Me: close($_[0]) failed: $!";
150 return $_[0] =~ /\A=?(\d+)\z/;
154 return $1 if $_[0] =~ /\A=?(\d+)\z/; # deal with fh just being an fd
158 my $do_spawn = $^O eq 'os2' || $^O eq 'MSWin32';
162 my($package, $dad_wtr, $dad_rdr, $dad_err, @cmd) = @_;
163 my($dup_wtr, $dup_rdr, $dup_err, $kidpid);
165 # simulate autovivification of filehandles because
166 # it's too ugly to use @_ throughout to make perl do it for us
170 $dad_wtr = $_[1] = gensym unless defined $dad_wtr && length $dad_wtr;
171 $dad_rdr = $_[2] = gensym unless defined $dad_rdr && length $dad_rdr;
174 # must strip crud for croak to add back, or looks ugly
175 $@ =~ s/(?<=value attempted) at .*//s;
179 $dad_err ||= $dad_rdr;
181 $dup_wtr = ($dad_wtr =~ s/^[<>]&//);
182 $dup_rdr = ($dad_rdr =~ s/^[<>]&//);
183 $dup_err = ($dad_err =~ s/^[<>]&//);
185 # force unqualified filehandles into caller's package
186 $dad_wtr = qualify $dad_wtr, $package unless fh_is_fd($dad_wtr);
187 $dad_rdr = qualify $dad_rdr, $package unless fh_is_fd($dad_rdr);
188 $dad_err = qualify $dad_err, $package unless fh_is_fd($dad_err);
190 my $kid_rdr = gensym;
191 my $kid_wtr = gensym;
192 my $kid_err = gensym;
194 xpipe $kid_rdr, $dad_wtr if !$dup_wtr;
195 xpipe $dad_rdr, $kid_wtr if !$dup_rdr;
196 xpipe $dad_err, $kid_err if !$dup_err && $dad_err ne $dad_rdr;
198 $kidpid = $do_spawn ? -1 : xfork;
199 if ($kidpid == 0) { # Kid
200 # A tie in the parent should not be allowed to cause problems.
203 # If she wants to dup the kid's stderr onto her stdout I need to
204 # save a copy of her stdout before I put something else there.
205 if ($dad_rdr ne $dad_err && $dup_err
206 && xfileno($dad_err) == fileno(STDOUT)) {
208 xopen($tmp, ">&$dad_err");
213 xopen \*STDIN, "<&$dad_wtr" if fileno(STDIN) != xfileno($dad_wtr);
216 xopen \*STDIN, "<&=" . fileno $kid_rdr;
219 xopen \*STDOUT, ">&$dad_rdr" if fileno(STDOUT) != xfileno($dad_rdr);
222 xopen \*STDOUT, ">&=" . fileno $kid_wtr;
224 if ($dad_rdr ne $dad_err) {
226 # I have to use a fileno here because in this one case
227 # I'm doing a dup but the filehandle might be a reference
228 # (from the special case above).
229 xopen \*STDERR, ">&" . xfileno($dad_err)
230 if fileno(STDERR) != xfileno($dad_err);
233 xopen \*STDERR, ">&=" . fileno $kid_err;
236 xopen \*STDERR, ">&STDOUT" if fileno(STDERR) != fileno(STDOUT);
238 if ($cmd[0] eq '-') {
239 croak "Arguments don't make sense when the command is '-'"
244 exec @cmd # XXX: wrong process to croak from
245 or croak "$Me: exec of @cmd failed";
246 } elsif ($do_spawn) {
247 # All the bookkeeping of coincidence between handles is
248 # handled in spawn_with_handles.
252 $kid_rdr = \*{$dad_wtr};
253 push @close, $kid_rdr;
255 push @close, \*{$dad_wtr}, $kid_rdr;
258 $kid_wtr = \*{$dad_rdr};
259 push @close, $kid_wtr;
261 push @close, \*{$dad_rdr}, $kid_wtr;
263 if ($dad_rdr ne $dad_err) {
265 $kid_err = \*{$dad_err};
266 push @close, $kid_err;
268 push @close, \*{$dad_err}, $kid_err;
275 spawn_with_handles( [ { mode => 'r',
280 handle => \*STDOUT },
283 handle => \*STDERR },
289 xclose $kid_rdr if !$dup_wtr;
290 xclose $kid_wtr if !$dup_rdr;
291 xclose $kid_err if !$dup_err && $dad_rdr ne $dad_err;
292 # If the write handle is a dup give it away entirely, close my copy
294 xclose $dad_wtr if $dup_wtr;
296 select((select($dad_wtr), $| = 1)[0]); # unbuffer pipe
303 croak "open3(@_): not enough arguments";
305 return _open3 'open3', scalar caller, @_
308 sub spawn_with_handles {
309 my $fds = shift; # Fields: handle, mode, open_as
310 my $close_in_child = shift;
311 my ($fd, $pid, @saved_fh, $saved, %saved, @errs);
314 foreach $fd (@$fds) {
315 $fd->{tmp_copy} = IO::Handle->new_from_fd($fd->{handle}, $fd->{mode});
316 $saved{fileno $fd->{handle}} = $fd->{tmp_copy};
318 foreach $fd (@$fds) {
319 bless $fd->{handle}, 'IO::Handle'
320 unless eval { $fd->{handle}->isa('IO::Handle') } ;
321 # If some of handles to redirect-to coincide with handles to
322 # redirect, we need to use saved variants:
323 $fd->{handle}->fdopen($saved{fileno $fd->{open_as}} || $fd->{open_as},
326 unless ($^O eq 'MSWin32') {
327 # Stderr may be redirected below, so we save the err text:
328 foreach $fd (@$close_in_child) {
329 fcntl($fd, Fcntl::F_SETFD(), 1) or push @errs, "fcntl $fd: $!"
330 unless $saved{fileno $fd}; # Do not close what we redirect!
335 $pid = eval { system 1, @_ }; # 1 == P_NOWAIT
336 push @errs, "IO::Pipe: Can't spawn-NOWAIT: $!" if !$pid || $pid < 0;
339 foreach $fd (@$fds) {
340 $fd->{handle}->fdopen($fd->{tmp_copy}, $fd->{mode});
341 $fd->{tmp_copy}->close or croak "Can't close: $!";
343 croak join "\n", @errs if @errs;
347 1; # so require is happy