125 lines
4.2 KiB
Perl
125 lines
4.2 KiB
Perl
package IPC::Open2;
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use strict;
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our ($VERSION, @ISA, @EXPORT);
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require 5.000;
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require Exporter;
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$VERSION = 1.05;
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@ISA = qw(Exporter);
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@EXPORT = qw(open2);
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=head1 NAME
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IPC::Open2 - open a process for both reading and writing using open2()
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=head1 SYNOPSIS
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use IPC::Open2;
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my $pid = open2(my $chld_out, my $chld_in,
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'some', 'cmd', 'and', 'args');
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# or passing the command through the shell
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my $pid = open2(my $chld_out, my $chld_in, 'some cmd and args');
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# read from parent STDIN and write to already open handle
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open my $outfile, '>', 'outfile.txt' or die "open failed: $!";
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my $pid = open2($outfile, '<&STDIN', 'some', 'cmd', 'and', 'args');
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# read from already open handle and write to parent STDOUT
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open my $infile, '<', 'infile.txt' or die "open failed: $!";
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my $pid = open2('>&STDOUT', $infile, 'some', 'cmd', 'and', 'args');
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# reap zombie and retrieve exit status
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waitpid( $pid, 0 );
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my $child_exit_status = $? >> 8;
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=head1 DESCRIPTION
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The open2() function runs the given command and connects $chld_out for
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reading and $chld_in for writing. It's what you think should work
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when you try
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my $pid = open(my $fh, "|cmd args|");
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The $chld_in filehandle will have autoflush turned on.
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If $chld_out 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 $chld_in is a string that begins with
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C<< <& >>, then $chld_in will be closed in the parent, and the child will
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read from it directly. In both cases, there will be a L<dup(2)> instead of a
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L<pipe(2)> made.
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If either reader or writer is the empty string or undefined, this will be
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replaced 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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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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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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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 L<bc(1)>, 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 L<bc(1)> will read a line at a time and
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output a line at a time. Programs like L<sort(1)> that read their
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entire input stream first, however, are quite apt to cause deadlock.
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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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The L<IO::Pty> and L<Expect> modules from CPAN can help with this, as
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they 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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=head1 WARNING
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The order of arguments differs from that of open3().
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=head1 SEE ALSO
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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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=cut
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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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require IPC::Open3;
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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', $_[1], $_[0], '>&STDERR', @_[2 .. $#_]);
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}
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1
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