IPC::Open3(3p) Perl Programmers Reference Guide IPC::Open3(3p)

IPC::Open3(3p) Perl Programmers Reference Guide IPC::Open3(3p) #

IPC::Open3(3p) Perl Programmers Reference Guide IPC::Open3(3p)

NNAAMMEE #

 IPC::Open3 - open a process for reading, writing, and error handling
 using open3()

SSYYNNOOPPSSIISS #

     use Symbol 'gensym'; # vivify a separate handle for STDERR
     my $pid = open3(my $chld_in, my $chld_out, my $chld_err = gensym,
                     'some', 'cmd', 'and', 'args');
     # or pass the command through the shell
     my $pid = open3(my $chld_in, my $chld_out, my $chld_err = gensym,
                     'some cmd and args');

     # read from parent STDIN
     # send STDOUT and STDERR to already open handle
     open my $outfile, '>>', 'output.txt' or die "open failed: $!";
     my $pid = open3('<&STDIN', $outfile, undef,
                     'some', 'cmd', 'and', 'args');

     # write to parent STDOUT and STDERR
     my $pid = open3(my $chld_in, '>&STDOUT', '>&STDERR',
                     'some', 'cmd', 'and', 'args');

     # reap zombie and retrieve exit status
     waitpid( $pid, 0 );
     my $child_exit_status = $? >> 8;

DDEESSCCRRIIPPTTIIOONN #

 Extremely similar to ooppeenn22(()), ooppeenn33(()) spawns the given command and
 connects $chld_out for reading from the child, $chld_in for writing to
 the child, and $chld_err for errors.  If $chld_err is false, or the same
 file descriptor as $chld_out, then STDOUT and STDERR of the child are on
 the same filehandle.  This means that an autovivified lexical cannot be
 used for the STDERR filehandle, but gensym from Symbol can be used to
 vivify a new glob reference, see "SYNOPSIS".  The $chld_in will have
 autoflush turned on.

 If $chld_in begins with "<&", then $chld_in will be closed in the parent,
 and the child will read from it directly.  If $chld_out or $chld_err
 begins with ">&", then the child will send output directly to that
 filehandle.  In both cases, there will be a dduupp(2) instead of a ppiippee(2)
 made.

 If either reader or writer is the empty string or undefined, this will be
 replaced by an autogenerated filehandle.  If so, you must pass a valid
 lvalue in the parameter slot so it can be overwritten in the caller, or
 an exception will be raised.

 The filehandles may also be integers, in which case they are understood
 as file descriptors.

 ooppeenn33(()) returns the process ID of the child process.  It doesn't return
 on failure: it just raises an exception matching "/^open3:/".  However,
 "exec" failures in the child (such as no such file or permission denied),
 are just reported to $chld_err under Windows and OS/2, as it is not
 possible to trap them.

 If the child process dies for any reason, the next write to $chld_in is
 likely to generate a SIGPIPE in the parent, which is fatal by default.
 So you may wish to handle this signal.

 Note if you specify "-" as the command, in an analogous fashion to
 "open(my $fh, "-|")" the child process will just be the forked Perl
 process rather than an external command.  This feature isn't yet
 supported on Win32 platforms.

 ooppeenn33(()) does not wait for and reap the child process after it exits.
 Except for short programs where it's acceptable to let the operating
 system take care of this, you need to do this yourself.  This is normally
 as simple as calling "waitpid $pid, 0" when you're done with the process.
 Failing to do this can result in an accumulation of defunct or "zombie"
 processes.  See "waitpid" in perlfunc for more information.

 If you try to read from the child's stdout writer and their stderr
 writer, you'll have problems with blocking, which means you'll want to
 use sseelleecctt(()) or IO::Select, which means you'd best use ssyyssrreeaadd(()) instead
 of rreeaaddlliinnee(()) for normal stuff.

 This is very dangerous, as you may block forever.  It assumes it's going
 to talk to something like bbcc(1), both writing to it and reading from it.
 This is presumably safe because you "know" that commands like bbcc(1) will
 read a line at a time and output a line at a time.  Programs like ssoorrtt(1)
 that read their entire input stream first, however, are quite apt to
 cause deadlock.

 The big problem with this approach is that if you don't have control over
 source code being run in the child process, you can't control what it
 does with pipe buffering.  Thus you can't just open a pipe to "cat -v"
 and continually read and write a line from it.

SSeeee AAllssoo IPC::Open2 Like Open3 but without STDERR capture.

 IPC::Run
     This is a CPAN module that has better error handling and more
     facilities than Open3.

WWAARRNNIINNGG #

 The order of arguments differs from that of ooppeenn22(()).

perl v5.36.3 2023-02-15 IPC::Open3(3p)