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Member "install-tl-20200916/tlpkg/tlperl/lib/IPC/Open2.pm" (20 Nov 2012, 4004 Bytes) of package /windows/misc/install-tl.zip:


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    1 package IPC::Open2;
    2 
    3 use strict;
    4 our ($VERSION, @ISA, @EXPORT);
    5 
    6 require 5.000;
    7 require Exporter;
    8 
    9 $VERSION    = 1.04;
   10 @ISA        = qw(Exporter);
   11 @EXPORT     = qw(open2);
   12 
   13 =head1 NAME
   14 
   15 IPC::Open2 - open a process for both reading and writing using open2()
   16 
   17 =head1 SYNOPSIS
   18 
   19     use IPC::Open2;
   20 
   21     $pid = open2(\*CHLD_OUT, \*CHLD_IN, 'some cmd and args');
   22       # or without using the shell
   23     $pid = open2(\*CHLD_OUT, \*CHLD_IN, 'some', 'cmd', 'and', 'args');
   24 
   25     # or with handle autovivification
   26     my($chld_out, $chld_in);
   27     $pid = open2($chld_out, $chld_in, 'some cmd and args');
   28       # or without using the shell
   29     $pid = open2($chld_out, $chld_in, 'some', 'cmd', 'and', 'args');
   30 
   31     waitpid( $pid, 0 );
   32     my $child_exit_status = $? >> 8;
   33 
   34 =head1 DESCRIPTION
   35 
   36 The open2() function runs the given $cmd and connects $chld_out for
   37 reading and $chld_in for writing.  It's what you think should work 
   38 when you try
   39 
   40     $pid = open(HANDLE, "|cmd args|");
   41 
   42 The write filehandle will have autoflush turned on.
   43 
   44 If $chld_out is a string (that is, a bareword filehandle rather than a glob
   45 or a reference) and it begins with C<< >& >>, then the child will send output
   46 directly to that file handle.  If $chld_in is a string that begins with
   47 C<< <& >>, then $chld_in will be closed in the parent, and the child will
   48 read from it directly.  In both cases, there will be a dup(2) instead of a
   49 pipe(2) made.
   50 
   51 If either reader or writer is the null string, this will be replaced
   52 by an autogenerated filehandle.  If so, you must pass a valid lvalue
   53 in the parameter slot so it can be overwritten in the caller, or
   54 an exception will be raised.
   55 
   56 open2() returns the process ID of the child process.  It doesn't return on
   57 failure: it just raises an exception matching C</^open2:/>.  However,
   58 C<exec> failures in the child are not detected.  You'll have to
   59 trap SIGPIPE yourself.
   60 
   61 open2() does not wait for and reap the child process after it exits.
   62 Except for short programs where it's acceptable to let the operating system
   63 take care of this, you need to do this yourself.  This is normally as
   64 simple as calling C<waitpid $pid, 0> when you're done with the process.
   65 Failing to do this can result in an accumulation of defunct or "zombie"
   66 processes.  See L<perlfunc/waitpid> for more information.
   67 
   68 This whole affair is quite dangerous, as you may block forever.  It
   69 assumes it's going to talk to something like B<bc>, both writing
   70 to it and reading from it.  This is presumably safe because you
   71 "know" that commands like B<bc> will read a line at a time and
   72 output a line at a time.  Programs like B<sort> that read their
   73 entire input stream first, however, are quite apt to cause deadlock.
   74 
   75 The big problem with this approach is that if you don't have control 
   76 over source code being run in the child process, you can't control
   77 what it does with pipe buffering.  Thus you can't just open a pipe to
   78 C<cat -v> and continually read and write a line from it.
   79 
   80 The IO::Pty and Expect modules from CPAN can help with this, as they
   81 provide a real tty (well, a pseudo-tty, actually), which gets you
   82 back to line buffering in the invoked command again.
   83 
   84 =head1 WARNING 
   85 
   86 The order of arguments differs from that of open3().
   87 
   88 =head1 SEE ALSO
   89 
   90 See L<IPC::Open3> for an alternative that handles STDERR as well.  This
   91 function is really just a wrapper around open3().
   92 
   93 =cut
   94 
   95 # &open2: tom christiansen, <tchrist@convex.com>
   96 #
   97 # usage: $pid = open2('rdr', 'wtr', 'some cmd and args');
   98 #    or  $pid = open2('rdr', 'wtr', 'some', 'cmd', 'and', 'args');
   99 #
  100 # spawn the given $cmd and connect $rdr for
  101 # reading and $wtr for writing.  return pid
  102 # of child, or 0 on failure.  
  103 # 
  104 # WARNING: this is dangerous, as you may block forever
  105 # unless you are very careful.  
  106 # 
  107 # $wtr is left unbuffered.
  108 # 
  109 # abort program if
  110 #   rdr or wtr are null
  111 #   a system call fails
  112 
  113 require IPC::Open3;
  114 
  115 sub open2 {
  116     local $Carp::CarpLevel = $Carp::CarpLevel + 1;
  117     return IPC::Open3::_open3('open2', $_[1], $_[0], '>&STDERR', @_[2 .. $#_]);
  118 }
  119 
  120 1