From @mjdominus

Created by @mjdominus

This program runs /bin/false, a standard unix command, on a piped
open, then closes the filehandle. /bin/false is the program which
exits immediately with exit status 1. According to the manual​:

  If the file handle came from a piped open C<close()> will
  additionally return FALSE if one of the other system calls
  involved fails or if the program exits with non-zero status.
  (If the only problem was that the program exited non-zero
  C<$!> will be set to C<0>.)

  [perlfunc/close]

Since /bin/false exited with non-zero status, $! should be set to 0.
However, it is instead set to the empty string.

  #!/usr/bin/perl
  open FH, "/bin/false |" or die "fork​: $!";
  print ">> $_" while <FH>;
  my $rc = close FH;
  my $errstr = defined($!) ? $! : "undefined";
  $rc = defined($rc) ? $rc : "undefined";
  print "close rc​: ($rc); \$!​: ($errstr); \$?​: ($?)\n";

The output is​:

  close rc​: (); $!​: (); $?​: (256)

If there is any version of Perl that has ever set $! to 0, I cannot
find it. Versions up through 5.003 set $! to `Illegal seek' (which I
guess is probably system-dependent) and versions 5.004 and later show
the behavior above.

Site configuration information for perl 5.00503:

Configured by mjd at Sun Jan 23 14:15:22 EST 2000.

Summary of my perl5 (5.0 patchlevel 5 subversion 3) configuration:
  Platform:
    osname=linux, osvers=2.2.12, archname=i586-linux
    uname='linux plover 2.2.12 #10 mon nov 1 17:02:09 est 1999 i586 unknown '
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=undef useperlio=undef d_sfio=undef
  Compiler:
    cc='cc', optimize='-O2', gccversion=egcs-2.90.29 980515 (egcs-1.0.3 release)
    cppflags='-Dbool=char -DHAS_BOOL -I/usr/local/include'
    ccflags ='-Dbool=char -DHAS_BOOL -I/usr/local/include'
    stdchar='char', d_stdstdio=define, usevfork=false
    intsize=4, longsize=4, ptrsize=4, doublesize=8
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    alignbytes=4, usemymalloc=n, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /shlib /lib /usr/lib
    libs=-lndbm -lgdbm -ldbm -ldb -ldl -lm -lc
    libc=/lib/libc.so.6, so=so, useshrplib=false, libperl=libperl.a
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic'
    cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib'

Locally applied patches:
    


@INC for perl 5.00503:
    /usr/lib/perl5/5.00503/i586-linux
    /usr/lib/perl5/5.00503
    /usr/lib/perl5/site_perl/5.005/i586-linux
    /usr/lib/perl5/site_perl/5.005
    .


Environment for perl 5.00503:
    HOME=/home/mjd
    LANG (unset)
    LANGUAGE (unset)
    LD_LIBRARY_PATH=/lib:/usr/lib:/usr/X11R6/lib
    LOGDIR (unset)
    PATH=/home/mjd/bin:/usr/local/bin:/bin:/usr/bin:/usr/X11/bin:/usr/games:/sbin:/usr/sbin:/usr/local/bin/X11:/usr/local/bin/mh:/data/mysql/bin:/home/mjd/TPI/bin:/usr/local/mysql/bin
    PERL_BADLANG (unset)
    SHELL=/bin/bash

From [Unknown Contact. See original ticket]

mjd@​plover.com writes​:

Since /bin/false exited with non-zero status, $! should be set to 0.
However, it is instead set to the empty string.

Do you remember that $! is double-headed? It has both numeric and
string values...

Ilya

From @mjdominus

mjd@​plover.com writes​:

Since /bin/false exited with non-zero status, $! should be set to 0.
However, it is instead set to the empty string.

Do you remember that $! is double-headed? It has both numeric and
string values...

Maybe the documentation is at fault, then. I don't see why the
current behavior is not simply described by

  If the only problem was that the program exited non-zero $!
  will be set to the empty string.

From [Unknown Contact. See original ticket]

On Mon, Feb 07, 2000 at 04​:19​:54PM -0500, Mark-Jason Dominus wrote​:

Do you remember that $! is double-headed? It has both numeric and
string values...

Maybe the documentation is at fault, then. I don't see why the
current behavior is not simply described by

If the only problem was that the program exited non\-zero $\!
will be set to the empty string\.

Because the value of $! *is not a string*.

Ilya

From @mjdominus

Because the value of $! *is not a string*.

If it were a string, how would the behvaior be different in this case?

From [Unknown Contact. See original ticket]

Maybe the documentation is at fault, then. I don't see why the
current behavior is not simply described by

If the only problem was that the program exited non\-zero $\!
will be set to the empty string\.

Because the value of $! *is not a string*.

Wrong. Back into the Sophist's hole with you. Just
looking for crap to pick at today, eh?

It can be a string.
It can be also a number.

And these are magically rather than canonically connected.

So what.

--tom