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package IPC::Open2; |
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|
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use strict; |
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our ($VERSION, @ISA, @EXPORT); |
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|
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require 5.000; |
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require Exporter; |
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|
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$VERSION = 1.01; |
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@ISA = qw(Exporter); |
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@EXPORT = qw(open2); |
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|
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=head1 NAME |
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|
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IPC::Open2, open2 - open a process for both reading and writing |
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|
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=head1 SYNOPSIS |
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|
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use IPC::Open2; |
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|
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$pid = open2(\*RDRFH, \*WTRFH, 'some cmd and args'); |
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# or without using the shell |
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$pid = open2(\*RDRFH, \*WTRFH, 'some', 'cmd', 'and', 'args'); |
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|
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# or with handle autovivification |
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my($rdrfh, $wtrfh); |
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$pid = open2($rdrfh, $wtrfh, 'some cmd and args'); |
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# or without using the shell |
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$pid = open2($rdrfh, $wtrfh, 'some', 'cmd', 'and', 'args'); |
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|
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=head1 DESCRIPTION |
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|
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The open2() function runs the given $cmd and connects $rdrfh for |
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reading and $wtrfh for writing. It's what you think should work |
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when you try |
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|
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$pid = open(HANDLE, "|cmd args|"); |
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|
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The write filehandle will have autoflush turned on. |
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|
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If $rdrfh is a string (that is, a bareword filehandle rather than a glob |
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or a reference) and it begins with C<< >& >>, then the child will send output |
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directly to that file handle. If $wtrfh is a string that begins with |
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C<< <& >>, then $wtrfh will be closed in the parent, and the child will read |
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from it directly. In both cases, there will be a dup(2) instead of a |
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pipe(2) made. |
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|
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If either reader or writer is the null string, this will be replaced |
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by an autogenerated filehandle. If so, you must pass a valid lvalue |
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in the parameter slot so it can be overwritten in the caller, or |
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an exception will be raised. |
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|
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open2() returns the process ID of the child process. It doesn't return on |
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failure: it just raises an exception matching C</^open2:/>. However, |
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C<exec> failures in the child are not detected. You'll have to |
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trap SIGPIPE yourself. |
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|
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open2() does not wait for and reap the child process after it exits. |
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Except for short programs where it's acceptable to let the operating system |
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take care of this, you need to do this yourself. This is normally as |
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simple as calling C<waitpid $pid, 0> when you're done with the process. |
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Failing to do this can result in an accumulation of defunct or "zombie" |
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processes. See L<perlfunc/waitpid> for more information. |
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|
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This whole affair is quite dangerous, as you may block forever. It |
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assumes it's going to talk to something like B<bc>, both writing |
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to it and reading from it. This is presumably safe because you |
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"know" that commands like B<bc> will read a line at a time and |
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output a line at a time. Programs like B<sort> that read their |
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entire input stream first, however, are quite apt to cause deadlock. |
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|
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The big problem with this approach is that if you don't have control |
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over source code being run in the child process, you can't control |
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what it does with pipe buffering. Thus you can't just open a pipe to |
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C<cat -v> and continually read and write a line from it. |
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|
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The IO::Pty and Expect modules from CPAN can help with this, as they |
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provide a real tty (well, a pseudo-tty, actually), which gets you |
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back to line buffering in the invoked command again. |
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|
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=head1 WARNING |
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|
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The order of arguments differs from that of open3(). |
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|
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=head1 SEE ALSO |
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|
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See L<IPC::Open3> for an alternative that handles STDERR as well. This |
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function is really just a wrapper around open3(). |
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|
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=cut |
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|
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# &open2: tom christiansen, <tchrist@convex.com> |
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# |
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# usage: $pid = open2('rdr', 'wtr', 'some cmd and args'); |
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# or $pid = open2('rdr', 'wtr', 'some', 'cmd', 'and', 'args'); |
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# |
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# spawn the given $cmd and connect $rdr for |
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# reading and $wtr for writing. return pid |
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# of child, or 0 on failure. |
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# |
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# WARNING: this is dangerous, as you may block forever |
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# unless you are very careful. |
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# |
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# $wtr is left unbuffered. |
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# |
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# abort program if |
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# rdr or wtr are null |
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# a system call fails |
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|
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require IPC::Open3; |
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|
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sub open2 { |
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local $Carp::CarpLevel = $Carp::CarpLevel + 1; |
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return IPC::Open3::_open3('open2', scalar caller, |
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$_[1], $_[0], '>&STDERR', @_[2 .. $#_]); |
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} |
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