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open2 acts very strange when STDOUT is redirected. #12748

Open p5pRT opened 11 years ago

p5pRT commented 11 years ago

Migrated from rt.perl.org#116589 (status was 'open')

Searchable as RT116589$

p5pRT commented 11 years ago

From xungeng@gmail.com

Created by xungeng@gmail.com

see this example​: xungeng@​debian​:\~/work/test/test$ cat foo #!/usr/bin/perl use FileHandle; use IPC​::Open2; use IO​::Handle;

#*STDOUT = IO​::Handle->new;

for (1..3) {   print STDERR "Loop​: $_\n";   $pid = open2( \*Reader\, \*Writer\, "cat" );   Writer->autoflush(); # default here\, actually   print Writer "stuff\n";   $got = \;   print STDERR $got; } xungeng@​debian​:\~/work/test/test$ cat bar #!/usr/bin/perl use FileHandle; use IPC​::Open2; use IO​::Handle;

*STDOUT = IO​::Handle->new;

for (1..3) {   print STDERR "Loop​: $_\n";   $pid = open2( \*Reader\, \*Writer\, "cat" );   Writer->autoflush(); # default here\, actually   print Writer "stuff\n";   $got = \;   print STDERR $got; } xungeng@​debian​:\~/work/test/test$ ./foo > /dev/null Loop​: 1 stuff Loop​: 2 stuff Loop​: 3 stuff xungeng@​debian​:\~/work/test/test$ ./bar > /dev/null Loop​: 1 Loop​: 2 Loop​: 3

the difference between foo and bar is only that STDOUT redirected or not.

when STDOUT is redirected\, open2 make the child process write to the old STDOUT\, not the child_out handler (\*Reader in this example).

Perl Info ``` Flags: category=library severity=high module=IPC::Open2 Site configuration information for perl 5.14.2: Configured by Debian Project at Mon Dec 10 13:17:22 UTC 2012. Summary of my perl5 (revision 5 version 14 subversion 2) configuration: Platform: osname=linux, osvers=3.2.0-4-686-pae, archname=i486-linux-gnu-thread-multi-64int uname='linux callisto 3.2.0-4-686-pae #1 smp debian 3.2.32-1 i686 gnulinux ' config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -D_FORTIFY_SOURCE=2 -g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security -Dldflags= -Wl,-z,relro -Dlddlflags=-shared -Wl,-z,relro -Dcccdlflags=-fPIC -Darchname=i486-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.14 -Darchlib=/usr/lib/perl/5.14 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.14.2 -Dsitearch=/usr/local/lib/perl/5.14.2 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man3 -Duse64bitint -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Ud_ualarm -Uusesfio -Uusenm -Ui_libutil -DDEBUGGING=-g -Doptimize=-O2 -Duseshrplib -Dlibperl=libperl.so.5.14.2 -des' hint=recommended, useposix=true, d_sigaction=define useithreads=define, usemultiplicity=define useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef use64bitint=define, use64bitall=undef, uselongdouble=undef usemymalloc=n, bincompat5005=undef Compiler: cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fstack-protector -fno-strict-aliasing -pipe -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64', optimize='-O2 -g', cppflags='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fstack-protector -fno-strict-aliasing -pipe -I/usr/local/include' ccversion='', gccversion='4.7.2', gccosandvers='' intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=12345678 d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12 ivtype='long long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8 alignbytes=4, prototype=define Linker and Libraries: ld='cc', ldflags =' -fstack-protector -L/usr/local/lib' libpth=/usr/local/lib /lib/i386-linux-gnu /lib/../lib /usr/lib/i386-linux-gnu /usr/lib/../lib /lib /usr/lib libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt perllibs=-ldl -lm -lpthread -lc -lcrypt libc=, so=so, useshrplib=true, libperl=libperl.so.5.14.2 gnulibc_version='2.13' Dynamic Linking: dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E' cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib -fstack-protector' Locally applied patches: @INC for perl 5.14.2: /etc/perl /usr/local/lib/perl/5.14.2 /usr/local/share/perl/5.14.2 /usr/lib/perl5 /usr/share/perl5 /usr/lib/perl/5.14 /usr/share/perl/5.14 /usr/local/lib/site_perl . Environment for perl 5.14.2: HOME=/home/xungeng LANG=en_US.UTF-8 LANGUAGE=en_US:en LD_LIBRARY_PATH=/usr/local/lib/ LOGDIR (unset) PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games:/home/xungeng/bin:/usr/local/go/bin PERL_BADLANG (unset) SHELL=/bin/bash ```
p5pRT commented 11 years ago

From @iabyn

On Tue\, Jan 29\, 2013 at 10​:38​:14PM -0800\, Xungeng Lee wrote​:

see this example​: xungeng@​debian​:\~/work/test/test$ cat foo #!/usr/bin/perl use FileHandle; use IPC​::Open2; use IO​::Handle;

#*STDOUT = IO​::Handle->new;

for (1..3) { print STDERR "Loop​: $_\n"; $pid = open2( \*Reader\, \*Writer\, "cat" ); Writer->autoflush(); # default here\, actually print Writer "stuff\n"; $got = \; print STDERR $got; } xungeng@​debian​:\~/work/test/test$ cat bar #!/usr/bin/perl use FileHandle; use IPC​::Open2; use IO​::Handle;

*STDOUT = IO​::Handle->new;

for (1..3) { print STDERR "Loop​: $_\n"; $pid = open2( \*Reader\, \*Writer\, "cat" ); Writer->autoflush(); # default here\, actually print Writer "stuff\n"; $got = \; print STDERR $got; } xungeng@​debian​:\~/work/test/test$ ./foo > /dev/null Loop​: 1 stuff Loop​: 2 stuff Loop​: 3 stuff xungeng@​debian​:\~/work/test/test$ ./bar > /dev/null Loop​: 1 Loop​: 2 Loop​: 3

the difference between foo and bar is only that STDOUT redirected or not.

when STDOUT is redirected\, open2 make the child process write to the old STDOUT\, not the child_out handler (\*Reader in this example).

Well for stdout\, IPC​::Open3 (which IPC​::Open2 calls out to) does essentially​:

  pipe(\*Reader\, \*FOO);   fork();   if (child) {   close(Writer);   open(STDOUT\, ">&=" . fileno(FOO));   exec($cmd);   }

i.e. it dups the file handle of the pipe to whatever file handle STDOUT maps to. If STDOUT doesn't point to file handle 1\, then it won't work.

I don't understand Open3.pm enough to decide whether it's unreasonable for it to handle a non-1 STDOUT (etc) or not.

-- Any [programming] language that doesn't occasionally surprise the novice will pay for it by continually surprising the expert.   -- Larry Wall

p5pRT commented 11 years ago

The RT System itself - Status changed from 'new' to 'open'