do FILE does not set $? (like cat FILE would)

[p5pRT]

Migrated from rt.perl.org#116713 (status was 'resolved')

Searchable as RT116713$

[p5pRT]

From @jimav

This is a bug report for perl from james_avera@​yahoo.com,
generated with the help of perlbug 1.39 running under perl 5.14.2.

---

perlfunc for 'do' says​:

" do 'stat.pl';
is just like
  eval `cat stat.pl`;
except [all those good things...]"

However $? is not being set, which is different than eval `cat ...`
and also prevents reliable detection of a missing file.

Suggest making 'do EXPR' set $? (and $!), or else update the docs
to add this to the list of differences from `cat ...`.

#!/usr/bin/perl
use strict; use warnings;
sub u($) { defined($_[0]) ? $_[0] : "undef" }

$? = 33;
my $r1 = do "/dev/null";
print "do '/dev/null' returned ",u($r1)," and \$?=$?\n";

$? = 44;
my $r2 = eval `cat /dev/null`;
print "eval 'cat...' returned ",u($r2)," and \$?=$?\n";

---

---

Flags​:
  category=docs
  severity=low

---

Site configuration information for perl 5.14.2​:

Configured by Debian Project at Tue Nov 27 00​:34​:23 UTC 2012.

Summary of my perl5 (revision 5 version 14 subversion 2) configuration​:
 
  Platform​:
  osname=linux, osvers=2.6.42-32-generic, archname=x86_64-linux-gnu-thread-multi
  uname='linux allspice 2.6.42-32-generic #51-ubuntu smp wed sep 26 21​:33​:09 utc 2012 x86_64 x86_64 x86_64 gnulinux '
  config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dcccdlflags=-fPIC -Darchname=x86_64-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=define, 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='4.6.3', gccosandvers=''
  intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
  ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
  alignbytes=8, prototype=define
  Linker and Libraries​:
  ld='cc', ldflags =' -fstack-protector -L/usr/local/lib'
  libpth=/usr/local/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-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='2.15'
  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​:
 

---

@​INC for perl 5.14.2​:
  /home/jima/lib/perl
  /home/jima/perl5/lib/perl5/x86_64-linux-gnu-thread-multi
  /home/jima/perl5/lib/perl5/x86_64-linux-gnu-thread-multi
  /home/jima/perl5/lib/perl5
  /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/jima
  LANG=en_US.UTF-8
  LANGUAGE=
  LD_LIBRARY_PATH=/home/jima/local/lib
  LOGDIR (unset)
  PATH=/home/jima/perl5/bin​:/home/jima/bin​:/home/jima/local/bin​:/home/jima/jima_tools/bin​:/usr/bin​:/bin​:/usr/sbin​:/sbin​:/usr/bin/X11​:/usr/local/bin​:/usr/local/sbin​:/usr/games​:.
  PERL5LIB=/home/jima/lib/perl​:/home/jima/perl5/lib/perl5/x86_64-linux-gnu-thread-multi​:/home/jima/perl5/lib/perl5
  PERL_BADLANG (unset)
  PERL_LOCAL_LIB_ROOT=/home/jima/perl5
  PERL_MB_OPT=--install_base /home/jima/perl5
  PERL_MM_OPT=INSTALL_BASE=/home/jima/perl5
  SHELL=/bin/bash

[p5pRT]

From @arc

Jim Avera <perlbug-followup@​perl.org> wrote​:

perlfunc for 'do' says​:

" do 'stat.pl';
is just like
eval `cat stat.pl`;
except [all those good things...]"

However $? is not being set, which is different than eval `cat ...`

Well, $? (aka $CHILD_ERROR) is the variable that contains the exit
status of the last process run. When you do "eval `cat $file`", that
involves running cat(1), so there is, as expected, a process whose
status can be reported.

But plain "do $file" doesn't need to create a process, and I think
it's correct that it doesn't. So I don't expect it to set $?.

and also prevents reliable detection of a missing file.

That can already be done by examining $!​:

$ perl -wE 'for my $f (qw</dev/null /nope>) { my ($r, $err, $exn) =
map $_ // "<undef>", scalar(do $f), $!, $@​; say "$f​: r=$r exn=$exn
err=$err" }'
/dev/null​: r=<undef> exn= err=
/nope​: r=<undef> exn= err=No such file or directory

Suggest making 'do EXPR' set $? (and $!), or else update the docs
to add this to the list of differences from `cat ...`.

Would this documentation change be good enough in your view?

Inline Patch

diff --git i/pod/perlfunc.pod w/pod/perlfunc.pod
index 0541bfd..2962a95 100644
--- i/pod/perlfunc.pod
+++ w/pod/perlfunc.pod
@@ -1558,11 +1558,11 @@ file as a Perl script.

     do 'stat.pl';

-is just like
+is largely like

     eval `cat stat.pl`;

-except that it's more efficient and concise, keeps track of the current
+except that it's more concise, runs no external processes, keeps

track of the current filename for error messages\, searches the C\<@​INC> directories\, and updates C\<%INC> if the file is found\. See L\ and L\ for these variables\. It also differs in that code evaluated with C\

--
Aaron Crane ** http​://aaroncrane.co.uk/

[p5pRT]

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

[p5pRT]

From @arc

I haven't heard back from you, but I'm assuming that wording change helps enough.

Applied as c319391

Thanks.

--
Aaron Crane ** http​://aaroncrane.co.uk/

[p5pRT]

@arc - Status changed from 'open' to 'resolved'

[p5pRT]

From @jimav

On 02/11/2013 02​:46 AM, Aaron Crane via RT wrote​:

That [detecting missing file] already be done by examining $! ...

(sorry for the delay, I've been swamped).
Thank you for pointing out that $! is set by "do FILE". I was
thinking wrongly.
Best,
-Jim