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docs perlfunc system() and SIGINT #10373

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p5pRT opened this issue May 11, 2010 · 5 comments
Open

docs perlfunc system() and SIGINT #10373

p5pRT opened this issue May 11, 2010 · 5 comments
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distro-Linux documentation type-OS-interaction

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@p5pRT
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p5pRT commented May 11, 2010

Migrated from rt.perl.org#75052 (status was 'open')

Searchable as RT75052$
@p5pRT
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p5pRT commented May 11, 2010

From user42@zip.com.au

The perlfunc.pod docs for system() start by saying it's the same as
fork+exec, but I see that's only in respect of the parameters, that the
SIGINT/SIGQUIT handling (described later on) is subtly different from
fork+exec. I wonder if it could be reworded a bit for clarity. Maybe
something like

  Run a program or a shell command and return its exit status.
  C<SIGINT> and C<SIGQUIT> act on the child but are ignored by the
  Perl parent. The parameters are the same as for C<exec LIST>.
  Note that argument processing varies depending on the number of
  arguments ...

Perl Info 

Flags:
    category=docs
    severity=medium

Site configuration information for perl 5.10.1:

Configured by Debian Project at Sun Apr 11 22:31:36 UTC 2010.

Summary of my perl5 (revision 5 version 10 subversion 1) configuration:
   
  Platform:
    osname=linux, osvers=2.6.32.11-dsa-ia32, archname=i486-linux-gnu-thread-multi
    uname='linux murphy 2.6.32.11-dsa-ia32 #1 smp fri apr 2 10:32:00 cest 2010 i686 gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dcccdlflags=-fPIC -Darchname=i486-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.10 -Darchlib=/usr/lib/perl/5.10 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.10.1 -Dsitearch=/usr/local/lib/perl/5.10.1 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man3 -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Ud_ualarm -Uusesfio -Uusenm -DDEBUGGING=-g -Doptimize=-O2 -Duseshrplib -Dlibperl=libperl.so.5.10.1 -Dd_dosuid -des'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=undef, use64bitall=undef, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2 -g',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.4.3', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long', ivsize=4, 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 /usr/lib /usr/lib64
    libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=/lib/libc-2.10.2.so, so=so, useshrplib=true, libperl=libperl.so.5.10.1
    gnulibc_version='2.10.2'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -g -L/usr/local/lib -fstack-protector'

Locally applied patches:
    DEBPKG:debian/arm_thread_stress_timeout - http://bugs.debian.org/501970 Raise the timeout of ext/threads/shared/t/stress.t to accommodate slower build hosts
    DEBPKG:debian/cpan_config_path - Set location of CPAN::Config to /etc/perl as /usr may not be writable.
    DEBPKG:debian/cpan_definstalldirs - Provide a sensible INSTALLDIRS default for modules installed from CPAN.
    DEBPKG:debian/db_file_ver - http://bugs.debian.org/340047 Remove overly restrictive DB_File version check.
    DEBPKG:debian/doc_info - Replace generic man(1) instructions with Debian-specific information.
    DEBPKG:debian/enc2xs_inc - http://bugs.debian.org/290336 Tweak enc2xs to follow symlinks and ignore missing @INC directories.
    DEBPKG:debian/errno_ver - http://bugs.debian.org/343351 Remove Errno version check due to upgrade problems with long-running processes.
    DEBPKG:debian/extutils_hacks - Various debian-specific ExtUtils changes
    DEBPKG:debian/fakeroot - Postpone LD_LIBRARY_PATH evaluation to the binary targets.
    DEBPKG:debian/instmodsh_doc - Debian policy doesn't install .packlist files for core or vendor.
    DEBPKG:debian/ld_run_path - Remove standard libs from LD_RUN_PATH as per Debian policy.
    DEBPKG:debian/libnet_config_path - Set location of libnet.cfg to /etc/perl/Net as /usr may not be writable.
    DEBPKG:debian/m68k_thread_stress - http://bugs.debian.org/495826 Disable some threads tests on m68k for now due to missing TLS.
    DEBPKG:debian/mod_paths - Tweak @INC ordering for Debian
    DEBPKG:debian/module_build_man_extensions - http://bugs.debian.org/479460 Adjust Module::Build manual page extensions for the Debian Perl policy
    DEBPKG:debian/perl_synopsis - http://bugs.debian.org/278323 Rearrange perl.pod
    DEBPKG:debian/prune_libs - http://bugs.debian.org/128355 Prune the list of libraries wanted to what we actually need.
    DEBPKG:debian/use_gdbm - Explicitly link against -lgdbm_compat in ODBM_File/NDBM_File. 
    DEBPKG:fixes/assorted_docs - http://bugs.debian.org/443733 [384f06a] Math::BigInt::CalcEmu documentation grammar fix
    DEBPKG:fixes/net_smtp_docs - http://bugs.debian.org/100195 [rt.cpan.org #36038] Document the Net::SMTP 'Port' option
    DEBPKG:fixes/processPL - http://bugs.debian.org/357264 [rt.cpan.org #17224] Always use PERLRUNINST when building perl modules.
    DEBPKG:debian/perlivp - http://bugs.debian.org/510895 Make perlivp skip include directories in /usr/local
    DEBPKG:fixes/pod2man-index-backslash - http://bugs.debian.org/521256 Escape backslashes in .IX entries
    DEBPKG:debian/disable-zlib-bundling - Disable zlib bundling in Compress::Raw::Zlib
    DEBPKG:fixes/kfreebsd_cppsymbols - http://bugs.debian.org/533098 [3b910a0] Add gcc predefined macros to $Config{cppsymbols} on GNU/kFreeBSD.
    DEBPKG:debian/cpanplus_definstalldirs - http://bugs.debian.org/533707 Configure CPANPLUS to use the site directories by default.
    DEBPKG:debian/cpanplus_config_path - Save local versions of CPANPLUS::Config::System into /etc/perl.
    DEBPKG:fixes/kfreebsd-filecopy-pipes - http://bugs.debian.org/537555 [16f708c] Fix File::Copy::copy with pipes on GNU/kFreeBSD
    DEBPKG:fixes/anon-tmpfile-dir - http://bugs.debian.org/528544 [perl #66452] Honor TMPDIR when open()ing an anonymous temporary file
    DEBPKG:fixes/abstract-sockets - http://bugs.debian.org/329291 [89904c0] Add support for Abstract namespace sockets.
    DEBPKG:fixes/hurd_cppsymbols - http://bugs.debian.org/544307 [eeb92b7] Add gcc predefined macros to $Config{cppsymbols} on GNU/Hurd.
    DEBPKG:fixes/autodie-flock - http://bugs.debian.org/543731 Allow for flock returning EAGAIN instead of EWOULDBLOCK on linux/parisc
    DEBPKG:fixes/archive-tar-instance-error - http://bugs.debian.org/539355 [rt.cpan.org #48879] Separate Archive::Tar instance error strings from each other
    DEBPKG:fixes/positive-gpos - http://bugs.debian.org/545234 [perl #69056] [c584a96] Fix \\G crash on first match
    DEBPKG:debian/devel-ppport-ia64-optim - http://bugs.debian.org/548943 Work around an ICE on ia64
    DEBPKG:fixes/trie-logic-match - http://bugs.debian.org/552291 [perl #69973] [0abd0d7] Fix a DoS in Unicode processing [CVE-2009-3626]
    DEBPKG:fixes/hppa-thread-eagain - http://bugs.debian.org/554218 make the threads-shared test suite more robust, fixing failures on hppa
    DEBPKG:fixes/crash-on-undefined-destroy - http://bugs.debian.org/564074 [perl #71952] [1f15e67] Fix a NULL pointer dereference when looking for a DESTROY method
    DEBPKG:fixes/tainted-errno - http://bugs.debian.org/574129 [perl #61976] [be1cf43] fix an errno stringification bug in taint mode
    DEBPKG:patchlevel - http://bugs.debian.org/567489 List packaged patches for 5.10.1-12 in patchlevel.h

@p5pRT
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p5pRT commented May 12, 2010

From @xdg

On Tue, May 11, 2010 at 6​:15 PM, Kevin Ryde <perlbug-followup@​perl.org> wrote​:

   Run a program or a shell command and return its exit status.
   C<SIGINT> and C<SIGQUIT> act on the child but are ignored by the
   Perl parent.  The parameters are the same as for C<exec LIST>.
   Note that argument processing varies depending on the number of
   arguments ...

There are some subtle portability issues in that statement, since
Win32 emulates the signals and a CTRL-C sends a signal that reaches
all processes attached to the console, including the parent.

-- David

@p5pRT
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p5pRT commented May 12, 2010

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

@p5pRT
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p5pRT commented May 12, 2010

From ben@morrow.me.uk

Quoth xdaveg@​gmail.com (David Golden)​:

On Tue, May 11, 2010 at 6​:15 PM, Kevin Ryde <perlbug-followup@​perl.org> wrote​:

   Run a program or a shell command and return its exit status.
   C<SIGINT> and C<SIGQUIT> act on the child but are ignored by the
   Perl parent.  The parameters are the same as for C<exec LIST>.
   Note that argument processing varies depending on the number of
   arguments ...

There are some subtle portability issues in that statement, since
Win32 emulates the signals and a CTRL-C sends a signal that reaches
all processes attached to the console, including the parent.

The whole of the first paragraph of perldoc -f system is unportable.
Non-Unix systems don't use fork/exec at all, and many Unixes use vfork,
for instance.

I feel a better approach to system/exec would be to document system
first ('runs an external command as a separate process'), and then
document exec as 'like system, but replaces the current process instead
of creating a new one'.

Ben

@p5pRT
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p5pRT commented May 15, 2010

From user42@zip.com.au

"David Golden via RT" <perlbug-followup@​perl.org> writes​:

There are some subtle portability issues in that statement, since
Win32 emulates the signals and a CTRL-C sends a signal that reaches
all processes attached to the console, including the parent.

Ah dear. That's probably undesirable. There's no doubt a place for
both ignoring and not, but you'd like it applied consistently.

I suppose the reason for the signal handling in the corresponding C
library system() func is to let ^C be caught in an interactive child
process without killing off the parent. That could be helpfully worked
into the description to show the motivation, if some compact words can
be found.

Incidentally where I wrote "... act on the child" it ought to be
"... inherited by the child" of course. If already ignoring in the
parent then the child starts life ignoring too.

@xenu xenu removed the affects-5.10 label Nov 19, 2021
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