initial checkin

git-svn-id: https://ws10smt.googlecode.com/svn/trunk@2 ec762483-ff6d-05da-a07a-a48fb63a330f

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diff --git a/tests/IPC/Run3.pm b/tests/IPC/Run3.pm
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+++ b/tests/IPC/Run3.pm
@@ -0,0 +1,850 @@
+package IPC::Run3;
+BEGIN { require 5.006_000; } # i.e. 5.6.0
+use strict;
+
+=head1 NAME
+
+IPC::Run3 - run a subprocess with input/ouput redirection
+
+=head1 VERSION
+
+version 0.043
+
+=cut
+
+our $VERSION = '0.043';
+
+=head1 SYNOPSIS
+
+    use IPC::Run3;    # Exports run3() by default
+
+    run3 \@cmd, \$in, \$out, \$err;
+
+=head1 DESCRIPTION
+
+This module allows you to run a subprocess and redirect stdin, stdout,
+and/or stderr to files and perl data structures.  It aims to satisfy 99% of the
+need for using C<system>, C<qx>, and C<open3> 
+with a simple, extremely Perlish API.
+
+Speed, simplicity, and portability are paramount.  (That's speed of Perl code;
+which is often much slower than the kind of buffered I/O that this module uses
+to spool input to and output from the child command.)
+
+=cut
+
+use Exporter;
+our @ISA = qw(Exporter);
+our @EXPORT = qw( run3 );
+our %EXPORT_TAGS = ( all => \@EXPORT );
+
+use constant debugging => $ENV{IPCRUN3DEBUG} || $ENV{IPCRUNDEBUG} || 0;
+use constant profiling => $ENV{IPCRUN3PROFILE} || $ENV{IPCRUNPROFILE} || 0;
+use constant is_win32  => 0 <= index $^O, "Win32";
+
+BEGIN {
+   if ( is_win32 ) {
+      eval "use Win32 qw( GetOSName ); 1" or die $@;
+   }
+}
+
+#use constant is_win2k => is_win32 && GetOSName() =~ /Win2000/i;
+#use constant is_winXP => is_win32 && GetOSName() =~ /WinXP/i;
+
+use Carp qw( croak );
+use File::Temp qw( tempfile );
+use POSIX qw( dup dup2 );
+
+# We cache the handles of our temp files in order to
+# keep from having to incur the (largish) overhead of File::Temp
+my %fh_cache;
+my $fh_cache_pid = $$;
+
+my $profiler;
+
+sub _profiler { $profiler } # test suite access
+
+BEGIN {
+    if ( profiling ) {
+        eval "use Time::HiRes qw( gettimeofday ); 1" or die $@;
+        if ( $ENV{IPCRUN3PROFILE} =~ /\A\d+\z/ ) {
+            require IPC::Run3::ProfPP;
+            IPC::Run3::ProfPP->import;
+            $profiler = IPC::Run3::ProfPP->new(Level => $ENV{IPCRUN3PROFILE});
+        } else {
+            my ( $dest, undef, $class ) =
+               reverse split /(=)/, $ENV{IPCRUN3PROFILE}, 2;
+            $class = "IPC::Run3::ProfLogger"
+                unless defined $class && length $class;
+            if ( not eval "require $class" ) {
+                my $e = $@;
+                $class = "IPC::Run3::$class";
+                eval "require IPC::Run3::$class" or die $e;
+            }
+            $profiler = $class->new( Destination => $dest );
+        }
+        $profiler->app_call( [ $0, @ARGV ], scalar gettimeofday() );
+    }
+}
+
+
+END {
+    $profiler->app_exit( scalar gettimeofday() ) if profiling;
+}
+
+sub _binmode {
+    my ( $fh, $mode, $what ) = @_;
+    # if $mode is not given, then default to ":raw", except on Windows,
+    # where we default to ":crlf";
+    # otherwise if a proper layer string was given, use that,
+    # else use ":raw"
+    my $layer = !$mode
+	? (is_win32 ? ":crlf" : ":raw")
+	: ($mode =~ /^:/ ? $mode : ":raw");
+    warn "binmode $what, $layer\n" if debugging >= 2;
+
+    binmode $fh, ":raw" unless $layer eq ":raw";      # remove all layers first
+    binmode $fh, $layer or croak "binmode $layer failed: $!";
+}
+
+sub _spool_data_to_child {
+    my ( $type, $source, $binmode_it ) = @_;
+
+    # If undef (not \undef) passed, they want the child to inherit
+    # the parent's STDIN.
+    return undef unless defined $source;
+
+    my $fh;
+    if ( ! $type ) {
+        open $fh, "<", $source or croak "$!: $source";
+	_binmode($fh, $binmode_it, "STDIN");
+        warn "run3(): feeding file '$source' to child STDIN\n"
+            if debugging >= 2;
+    } elsif ( $type eq "FH" ) {
+        $fh = $source;
+        warn "run3(): feeding filehandle '$source' to child STDIN\n"
+            if debugging >= 2;
+    } else {
+        $fh = $fh_cache{in} ||= tempfile;
+        truncate $fh, 0;
+        seek $fh, 0, 0;
+	_binmode($fh, $binmode_it, "STDIN");
+        my $seekit;
+        if ( $type eq "SCALAR" ) {
+
+            # When the run3()'s caller asks to feed an empty file
+            # to the child's stdin, we want to pass a live file
+            # descriptor to an empty file (like /dev/null) so that
+            # they don't get surprised by invalid fd errors and get
+            # normal EOF behaviors.
+            return $fh unless defined $$source;  # \undef passed
+
+            warn "run3(): feeding SCALAR to child STDIN",
+                debugging >= 3
+                   ? ( ": '", $$source, "' (", length $$source, " chars)" )
+                   : (),
+                "\n"
+                if debugging >= 2;
+
+            $seekit = length $$source;
+            print $fh $$source or die "$! writing to temp file";
+
+        } elsif ( $type eq "ARRAY" ) {
+            warn "run3(): feeding ARRAY to child STDIN",
+                debugging >= 3 ? ( ": '", @$source, "'" ) : (),
+                "\n"
+            if debugging >= 2;
+
+            print $fh @$source or die "$! writing to temp file";
+            $seekit = grep length, @$source;
+        } elsif ( $type eq "CODE" ) {
+            warn "run3(): feeding output of CODE ref '$source' to child STDIN\n"
+                if debugging >= 2;
+            my $parms = [];  # TODO: get these from $options
+            while (1) {
+                my $data = $source->( @$parms );
+                last unless defined $data;
+                print $fh $data or die "$! writing to temp file";
+                $seekit = length $data;
+            }
+        }
+
+        seek $fh, 0, 0 or croak "$! seeking on temp file for child's stdin"
+            if $seekit;
+    }
+
+    croak "run3() can't redirect $type to child stdin"
+        unless defined $fh;
+
+    return $fh;
+}
+
+sub _fh_for_child_output {
+    my ( $what, $type, $dest, $options ) = @_;
+
+    my $fh;
+    if ( $type eq "SCALAR" && $dest == \undef ) {
+        warn "run3(): redirecting child $what to oblivion\n"
+            if debugging >= 2;
+
+        $fh = $fh_cache{nul} ||= do {
+            open $fh, ">", File::Spec->devnull;
+	    $fh;
+        };
+    } elsif ( $type eq "FH" ) {
+        $fh = $dest;
+        warn "run3(): redirecting $what to filehandle '$dest'\n"
+            if debugging >= 3;
+    } elsif ( !$type ) {
+        warn "run3(): feeding child $what to file '$dest'\n"
+            if debugging >= 2;
+
+        open $fh, $options->{"append_$what"} ? ">>" : ">", $dest 
+	    or croak "$!: $dest";
+    } else {
+        warn "run3(): capturing child $what\n"
+            if debugging >= 2;
+
+        $fh = $fh_cache{$what} ||= tempfile;
+        seek $fh, 0, 0;
+        truncate $fh, 0;
+    }
+
+    my $binmode_it = $options->{"binmode_$what"};
+    _binmode($fh, $binmode_it, uc $what);
+
+    return $fh;
+}
+
+sub _read_child_output_fh {
+    my ( $what, $type, $dest, $fh, $options ) = @_;
+
+    return if $type eq "SCALAR" && $dest == \undef;
+
+    seek $fh, 0, 0 or croak "$! seeking on temp file for child $what";
+
+    if ( $type eq "SCALAR" ) {
+        warn "run3(): reading child $what to SCALAR\n"
+            if debugging >= 3;
+
+        # two read()s are used instead of 1 so that the first will be
+        # logged even it reads 0 bytes; the second won't.
+        my $count = read $fh, $$dest, 10_000, 
+	    $options->{"append_$what"} ? length $$dest : 0;
+        while (1) {
+            croak "$! reading child $what from temp file"
+                unless defined $count;
+
+            last unless $count;
+
+            warn "run3(): read $count bytes from child $what",
+                debugging >= 3 ? ( ": '", substr( $$dest, -$count ), "'" ) : (),
+                "\n"
+                if debugging >= 2;
+
+            $count = read $fh, $$dest, 10_000, length $$dest;
+        }
+    } elsif ( $type eq "ARRAY" ) {
+	if ($options->{"append_$what"}) {
+	    push @$dest, <$fh>;
+	} else {
+	    @$dest = <$fh>;
+	}
+        if ( debugging >= 2 ) {
+            my $count = 0;
+            $count += length for @$dest;
+            warn
+                "run3(): read ",
+                scalar @$dest,
+                " records, $count bytes from child $what",
+                debugging >= 3 ? ( ": '", @$dest, "'" ) : (),
+                "\n";
+        }
+    } elsif ( $type eq "CODE" ) {
+        warn "run3(): capturing child $what to CODE ref\n"
+            if debugging >= 3;
+
+        local $_;
+        while ( <$fh> ) {
+            warn
+                "run3(): read ",
+                length,
+                " bytes from child $what",
+                debugging >= 3 ? ( ": '", $_, "'" ) : (),
+                "\n"
+                if debugging >= 2;
+
+            $dest->( $_ );
+        }
+    } else {
+        croak "run3() can't redirect child $what to a $type";
+    }
+
+}
+
+sub _type {
+    my ( $redir ) = @_;
+    return "FH" if eval { $redir->isa("IO::Handle") };
+    my $type = ref $redir;
+    return $type eq "GLOB" ? "FH" : $type;
+}
+
+sub _max_fd {
+    my $fd = dup(0);
+    POSIX::close $fd;
+    return $fd;
+}
+
+my $run_call_time;
+my $sys_call_time;
+my $sys_exit_time;
+
+sub run3 {
+    $run_call_time = gettimeofday() if profiling;
+
+    my $options = @_ && ref $_[-1] eq "HASH" ? pop : {};
+
+    my ( $cmd, $stdin, $stdout, $stderr ) = @_;
+
+    print STDERR "run3(): running ", 
+       join( " ", map "'$_'", ref $cmd ? @$cmd : $cmd ), 
+       "\n"
+       if debugging;
+
+    if ( ref $cmd ) {
+        croak "run3(): empty command"     unless @$cmd;
+        croak "run3(): undefined command" unless defined $cmd->[0];
+        croak "run3(): command name ('')" unless length  $cmd->[0];
+    } else {
+        croak "run3(): missing command" unless @_;
+        croak "run3(): undefined command" unless defined $cmd;
+        croak "run3(): command ('')" unless length  $cmd;
+    }
+
+    foreach (qw/binmode_stdin binmode_stdout binmode_stderr/) {
+	if (my $mode = $options->{$_}) {
+	    croak qq[option $_ must be a number or a proper layer string: "$mode"]
+		unless $mode =~ /^(:|\d+$)/;
+	}
+    }
+
+    my $in_type  = _type $stdin;
+    my $out_type = _type $stdout;
+    my $err_type = _type $stderr;
+
+    if ($fh_cache_pid != $$) {
+	# fork detected, close all cached filehandles and clear the cache
+	close $_ foreach values %fh_cache;
+	%fh_cache = ();
+	$fh_cache_pid = $$;
+    }
+    
+    # This routine procedes in stages so that a failure in an early
+    # stage prevents later stages from running, and thus from needing
+    # cleanup.
+
+    my $in_fh  = _spool_data_to_child $in_type, $stdin,
+        $options->{binmode_stdin} if defined $stdin;
+
+    my $out_fh = _fh_for_child_output "stdout", $out_type, $stdout,
+        $options if defined $stdout;
+
+    my $tie_err_to_out =
+        defined $stderr && defined $stdout && $stderr eq $stdout;
+
+    my $err_fh = $tie_err_to_out
+        ? $out_fh
+        : _fh_for_child_output "stderr", $err_type, $stderr,
+            $options if defined $stderr;
+
+    # this should make perl close these on exceptions
+#    local *STDIN_SAVE;
+    local *STDOUT_SAVE;
+    local *STDERR_SAVE;
+
+    my $saved_fd0 = dup( 0 ) if defined $in_fh;
+
+#    open STDIN_SAVE,  "<&STDIN"#  or croak "run3(): $! saving STDIN"
+#        if defined $in_fh;
+    open STDOUT_SAVE, ">&STDOUT" or croak "run3(): $! saving STDOUT"
+        if defined $out_fh;
+    open STDERR_SAVE, ">&STDERR" or croak "run3(): $! saving STDERR"
+        if defined $err_fh;
+
+    my $errno;
+    my $ok = eval {
+        # The open() call here seems to not force fd 0 in some cases;
+        # I ran in to trouble when using this in VCP, not sure why.
+        # the dup2() seems to work.
+        dup2( fileno $in_fh, 0 )
+#        open STDIN,  "<&=" . fileno $in_fh
+            or croak "run3(): $! redirecting STDIN"
+            if defined $in_fh;
+
+#        close $in_fh or croak "$! closing STDIN temp file"
+#            if ref $stdin;
+
+        open STDOUT, ">&" . fileno $out_fh
+            or croak "run3(): $! redirecting STDOUT"
+            if defined $out_fh;
+
+        open STDERR, ">&" . fileno $err_fh
+            or croak "run3(): $! redirecting STDERR"
+            if defined $err_fh;
+
+        $sys_call_time = gettimeofday() if profiling;
+
+        my $r = ref $cmd
+              ? system { $cmd->[0] }
+                       is_win32
+                           ? map {
+                                 # Probably need to offer a win32 escaping
+                                 # option, every command may be different.
+                                 ( my $s = $_ ) =~ s/"/"""/g;
+                                 $s = qq{"$s"};
+                                 $s;
+                             } @$cmd
+                           : @$cmd
+              : system $cmd;
+
+	$errno = $!;		# save $!, because later failures will overwrite it
+        $sys_exit_time = gettimeofday() if profiling;
+        if ( debugging ) {
+            my $err_fh = defined $err_fh ? \*STDERR_SAVE : \*STDERR;
+	    if ( defined $r && $r != -1 ) {
+		print $err_fh "run3(): \$? is $?\n";
+	    } else {
+		print $err_fh "run3(): \$? is $?, \$! is $errno\n";
+	    }
+        }
+
+        die $! if defined $r && $r == -1 && !$options->{return_if_system_error};
+
+        1;
+    };
+    my $x = $@;
+
+    my @errs;
+
+    if ( defined $saved_fd0 ) {
+        dup2( $saved_fd0, 0 );
+        POSIX::close( $saved_fd0 );
+    }
+
+#    open STDIN,  "<&STDIN_SAVE"#  or push @errs, "run3(): $! restoring STDIN"
+#        if defined $in_fh;
+    open STDOUT, ">&STDOUT_SAVE" or push @errs, "run3(): $! restoring STDOUT"
+        if defined $out_fh;
+    open STDERR, ">&STDERR_SAVE" or push @errs, "run3(): $! restoring STDERR"
+        if defined $err_fh;
+
+    croak join ", ", @errs if @errs;
+
+    die $x unless $ok;
+
+    _read_child_output_fh "stdout", $out_type, $stdout, $out_fh, $options
+        if defined $out_fh && $out_type && $out_type ne "FH";
+    _read_child_output_fh "stderr", $err_type, $stderr, $err_fh, $options
+        if defined $err_fh && $err_type && $err_type ne "FH" && !$tie_err_to_out;
+    $profiler->run_exit(
+       $cmd,
+       $run_call_time,
+       $sys_call_time,
+       $sys_exit_time,
+       scalar gettimeofday() 
+    ) if profiling;
+
+    $! = $errno;		# restore $! from system()
+
+    return 1;
+}
+
+1;
+
+__END__
+
+=head2 C<< run3($cmd, $stdin, $stdout, $stderr, \%options) >>
+
+All parameters after C<$cmd> are optional.
+
+The parameters C<$stdin>, C<$stdout> and C<$stderr> indicate
+how the child's corresponding filehandle 
+(C<STDIN>, C<STDOUT> and C<STDERR>, resp.) will be redirected.
+Because the redirects come last, this allows C<STDOUT> and C<STDERR> to default
+to the parent's by just not specifying them -- a common use case.
+
+C<run3> throws an exception if the wrapped C<system> call returned -1
+or anything went wrong with C<run3>'s processing of filehandles.
+Otherwise it returns true. 
+It leaves C<$?> intact for inspection of exit and wait status.
+
+Note that a true return value from C<run3> doesn't mean that the command
+had a successful exit code. Hence you should always check C<$?>.
+
+See L</%options> for an option to handle the case of C<system>
+returning -1 yourself.
+
+=head3 C<$cmd>
+
+Usually C<$cmd> will be an ARRAY reference and the child is invoked via
+
+  system @$cmd;
+
+But C<$cmd> may also be a string in which case the child is invoked via
+
+  system $cmd;
+
+(cf. L<perlfunc/system> for the difference and the pitfalls of using
+the latter form).
+
+=head3 C<$stdin>, C<$stdout>, C<$stderr>
+
+The parameters C<$stdin>, C<$stdout> and C<$stderr> 
+can take one of the following forms:
+
+=over 4
+
+=item C<undef> (or not specified at all)
+
+The child inherits the corresponding filehandle from the parent.
+
+  run3 \@cmd, $stdin;                   # child writes to same STDOUT and STDERR as parent
+  run3 \@cmd, undef, $stdout, $stderr;  # child reads from same STDIN as parent
+
+=item C<\undef>
+
+The child's filehandle is redirected from or to the
+local equivalent of C</dev/null> (as returned by 
+C<< File::Spec->devnull() >>).
+
+  run3 \@cmd, \undef, $stdout, $stderr; # child reads from /dev/null
+
+=item a simple scalar
+
+The parameter is taken to be the name of a file to read from
+or write to. In the latter case, the file will be opened via
+
+  open FH, ">", ...
+
+i.e. it is created if it doesn't exist and truncated otherwise.
+Note that the file is opened by the parent which will L<croak|Carp/croak>
+in case of failure.
+
+  run3 \@cmd, \undef, "out.txt";        # child writes to file "out.txt"
+
+=item a filehandle (either a reference to a GLOB or an C<IO::Handle>)
+
+The filehandle is inherited by the child.
+
+  open my $fh, ">", "out.txt";
+  print $fh "prologue\n";
+  ...
+  run3 \@cmd, \undef, $fh;              # child writes to $fh
+  ...
+  print $fh "epilogue\n";
+  close $fh;
+
+=item a SCALAR reference 
+
+The referenced scalar is treated as a string to be read from or
+written to. In the latter case, the previous content of the string
+is overwritten.
+
+  my $out;
+  run3 \@cmd, \undef, \$out;           # child writes into string 
+  run3 \@cmd, \<<EOF;                  # child reads from string (can use "here" notation)
+  Input
+  to 
+  child
+  EOF
+
+=item an ARRAY reference 
+
+For C<$stdin>, the elements of C<@$stdin> are simply spooled to the child.
+
+For C<$stdout> or C<$stderr>, the child's corresponding file descriptor 
+is read line by line (as determined by the current setting of C<$/>)
+into C<@$stdout> or C<@$stderr>, resp. The previous content of the array
+is overwritten.
+
+  my @lines;
+  run3 \@cmd, \undef, \@lines;         # child writes into array
+
+=item a CODE reference 
+
+For C<$stdin>, C<&$stdin> will be called repeatedly (with no arguments) and 
+the return values are spooled to the child. C<&$stdin> must signal the end of
+input by returning C<undef>. 
+
+For C<$stdout> or C<$stderr>, the child's corresponding file descriptor 
+is read line by line (as determined by the current setting of C<$/>)
+and C<&$stdout> or C<&$stderr>, resp., is called with the contents of the line.
+Note that there's no end-of-file indication.
+
+  my $i = 0;
+  sub producer {
+    return $i < 10 ? "line".$i++."\n" : undef;
+  }
+    
+  run3 \@cmd, \&producer;              # child reads 10 lines
+
+Note that this form of redirecting the child's I/O doesn't imply
+any form of concurrency between parent and child - run3()'s method of
+operation is the same no matter which form of redirection you specify.
+
+=back
+
+If the same value is passed for C<$stdout> and C<$stderr>, then the child
+will write both C<STDOUT> and C<STDERR> to the same filehandle.
+In general, this means that
+
+    run3 \@cmd, \undef, "foo.txt", "foo.txt";
+    run3 \@cmd, \undef, \$both, \$both;
+
+will DWIM and pass a single file handle to the child for both C<STDOUT> and
+C<STDERR>, collecting all into file "foo.txt" or C<$both>.
+
+=head3 C<\%options>
+
+The last parameter, C<\%options>, must be a hash reference if present. 
+
+Currently the following
+keys are supported: 
+
+=over 4
+
+=item C<binmode_stdin>, C<binmode_stdout>, C<binmode_stderr>
+
+The value must a "layer" as described in L<perlfunc/binmode>.
+If specified the corresponding
+parameter C<$stdin>, C<$stdout> or C<$stderr>, resp., operates
+with the given layer. 
+
+For backward compatibility, a true value that doesn't start with ":"
+(e.g. a number) is interpreted as ":raw". If the value is false
+or not specified, the default is ":crlf" on Windows and ":raw" otherwise.
+
+Don't expect that values other than the built-in layers ":raw", ":crlf",
+and (on newer Perls) ":bytes", ":utf8", ":encoding(...)" will work.
+
+=item C<append_stdout>, C<append_stderr>
+
+If their value is true then the corresponding
+parameter C<$stdout> or C<$stderr>, resp., will append the child's output
+to the existing "contents" of the redirector. This only makes
+sense if the redirector is a simple scalar (the corresponding file
+is opened in append mode), a SCALAR reference (the output is 
+appended to the previous contents of the string) 
+or an ARRAY reference (the output is C<push>ed onto the 
+previous contents of the array).
+
+=item C<return_if_system_error>
+
+If this is true C<run3> does B<not> throw an exception if C<system>
+returns -1 (cf. L<perlfunc/system> for possible
+failure scenarios.), but returns true instead.
+In this case C<$?> has the value -1 and C<$!> 
+contains the errno of the failing C<system> call.
+
+=back 
+
+=head1 HOW IT WORKS
+
+=over 4
+
+=item (1)
+
+For each redirector C<$stdin>, C<$stdout>, and C<$stderr>, 
+C<run3()> furnishes a filehandle:
+
+=over 4
+
+=item *
+
+if the redirector already specifies a filehandle it just uses that
+
+=item *
+
+if the redirector specifies a filename, C<run3()> opens the file
+in the appropriate mode
+
+=item *
+
+in all other cases, C<run3()> opens a temporary file 
+(using L<tempfile|Temp/tempfile>)
+
+=back
+
+=item (2)
+
+If C<run3()> opened a temporary file for C<$stdin> in step (1),
+it writes the data using the specified method (either
+from a string, an array or returnd by a function) to the temporary file and rewinds it.
+
+=item (3)
+
+C<run3()> saves the parent's C<STDIN>, C<STDOUT> and C<STDERR> by duplicating
+them to new filehandles. It duplicates the filehandles from step (1)
+to C<STDIN>, C<STDOUT> and C<STDERR>, resp.
+
+=item (4)
+
+C<run3()> runs the child by invoking L<system|perlfunc/system> 
+with C<$cmd> as specified above.
+
+=item (5)
+
+C<run3()> restores the parent's C<STDIN>, C<STDOUT> and C<STDERR> saved in step (3).
+
+=item (6)
+
+If C<run3()> opened a temporary file for C<$stdout> or C<$stderr> in step (1),
+it rewinds it and reads back its contents using the specified method 
+(either to a string, an array or by calling a function).
+
+=item (7)
+
+C<run3()> closes all filehandles that it opened explicitly in step (1).
+
+=back
+
+Note that when using temporary files, C<run3()> tries to amortize the overhead
+by reusing them (i.e. it keeps them open and rewinds and truncates them
+before the next operation).
+
+=head1 LIMITATIONS
+
+Often uses intermediate files (determined by File::Temp, and thus by the
+File::Spec defaults and the TMPDIR env. variable) for speed, portability and
+simplicity.
+
+Use extrem caution when using C<run3> in a threaded environment if
+concurrent calls of C<run3> are possible. Most likely, I/O from different
+invocations will get mixed up. The reason is that in most thread 
+implementations all threads in a process share the same STDIN/STDOUT/STDERR.
+Known failures are Perl ithreads on Linux and Win32. Note that C<fork>
+on Win32 is emulated via Win32 threads and hence I/O mix up is possible
+between forked children here (C<run3> is "fork safe" on Unix, though).
+
+=head1 DEBUGGING
+
+To enable debugging use the IPCRUN3DEBUG environment variable to
+a non-zero integer value:
+
+  $ IPCRUN3DEBUG=1 myapp
+
+=head1 PROFILING
+
+To enable profiling, set IPCRUN3PROFILE to a number to enable emitting profile
+information to STDERR (1 to get timestamps, 2 to get a summary report at the
+END of the program, 3 to get mini reports after each run) or to a filename to
+emit raw data to a file for later analysis.
+
+=head1 COMPARISON
+
+Here's how it stacks up to existing APIs:
+
+=head2 compared to C<system()>, C<qx''>, C<open "...|">, C<open "|...">
+
+=over
+
+=item + 
+
+redirects more than one file descriptor
+
+=item + 
+
+returns TRUE on success, FALSE on failure
+
+=item + 
+
+throws an error if problems occur in the parent process (or the pre-exec child)
+
+=item + 
+
+allows a very perlish interface to Perl data structures and subroutines
+
+=item + 
+
+allows 1 word invocations to avoid the shell easily:
+
+ run3 ["foo"];  # does not invoke shell
+
+=item - 
+
+does not return the exit code, leaves it in $?
+
+=back
+
+=head2 compared to C<open2()>, C<open3()>
+
+=over
+
+=item + 
+
+no lengthy, error prone polling/select loop needed
+
+=item +
+
+hides OS dependancies
+
+=item + 
+
+allows SCALAR, ARRAY, and CODE references to source and sink I/O
+
+=item + 
+
+I/O parameter order is like C<open3()>  (not like C<open2()>).
+
+=item - 
+
+does not allow interaction with the subprocess
+
+=back
+
+=head2 compared to L<IPC::Run::run()|IPC::Run/run>
+
+=over
+
+=item + 
+
+smaller, lower overhead, simpler, more portable
+
+=item +
+
+no select() loop portability issues
+
+=item +
+
+does not fall prey to Perl closure leaks
+
+=item -
+
+does not allow interaction with the subprocess (which
+IPC::Run::run() allows by redirecting subroutines)
+
+=item -
+
+lacks many features of C<IPC::Run::run()> (filters, pipes,
+redirects, pty support)
+
+=back
+
+=head1 COPYRIGHT
+
+Copyright 2003, R. Barrie Slaymaker, Jr., All Rights Reserved
+
+=head1 LICENSE
+
+You may use this module under the terms of the BSD, Artistic, or GPL licenses,
+any version.
+
+=head1 AUTHOR
+
+Barrie Slaymaker E<lt>C<barries@slaysys.com>E<gt>
+
+Ricardo SIGNES E<lt>C<rjbs@cpan.org>E<gt> performed some routine maintenance in
+2005, thanks to help from the following ticket and/or patch submitters: Jody
+Belka, Roderich Schupp, David Morel, and anonymous others.
+
+=cut