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)