GNU screen not seeing $SHELL env var?

GNU screen not seeing $SHELL env var?

[Tom Rodman]

Not sure when this problem started.  The issue:
GNU screen is starting w/an empty or undefined value for $SHELL, so
the login shell for all screen windows is incorrect:

  $ uname -a; cygcheck -c cygwin
  CYGWIN_NT-5.1 aqua 1.7.16s(0.261/5/3) 20120604 01:26:35 i686 Cygwin
  Cygwin Package Information
  Package              Version        Status
  cygwin               1.7.15-1       OK
  $ cygcheck -f /bin/screen
  screen-4.0.3-7
  $ grep SHELL ~/.screenrc
  shell -$SHELL
  $ echo $SHELL
  /bin/bash
  $ bash -c 'echo SHELL: $SHELL'  # does this prove SHELL is exported?
  SHELL: /bin/bash
  $ screen 
  --snip/switch to a separate shell to run [procps -wwH -o pid,ppid,user,tty,args -e]:
   5988  2200 adm_tsr  pty3       /bin/bash --login
   1492  5988 adm_tsr  pty3         screen
   4476  1492 adm_tsr  ?              SCREEN
   5420  4476 adm_tsr  pty4             -
  --snip/now to shell w/pid 5420 inside screen:
  $ echo SHELL: \[$SHELL]
  SHELL: []
  $ 

Notice above that pid 5420 is named '-', which corresponds
to /bin/sh, instead of /bin/bash.

  $ command ps -elW |grep 5420
  I    5420    4476    5420       2476  pty4    1008 07:54:08 /usr/bin/sh

The workaround is to export SHELL prior to starting screen.
I do not understand why that works, it seems that SHELL was already
exported, since (in a non screen login shell): 

   sh -c 'echo SHELL: $SHELL'

echos /bin/bash

Is anyone else seeing this issue?

--
thanks,
Tom

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Re: GNU screen not seeing $SHELL env var?

[Eric Blake]

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On 06/20/2012 07:20 AM, Tom Rodman wrote:

>   $ echo $SHELL
>   /bin/bash
>   $ bash -c 'echo SHELL: $SHELL'  # does this prove SHELL is exported?
>   SHELL: /bin/bash

No.  And in fact, bash does not export SHELL by default, but defaults to
defining SHELL as a shell-local variable.  You have to explicitly export
it yourself if you want child processes to see it.

$ env -u SHELL bash -c 'echo $SHELL'
/bin/bash
$ env -u SHELL bash -c 'env | grep SHELL'
$ env -u SHELL bash -c 'export SHELL; env | grep SHELL'
SHELL=/bin/bash
$

-- 
Eric Blake   eblake@redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org




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Re: GNU screen not seeing $SHELL env var?

[Tom Rodman]

On Wed 6/20/12 8:07 MDT Eric Blake wrote:
> On 06/20/2012 07:20 AM, Tom Rodman wrote:
> 
> >   $ echo $SHELL
> >   /bin/bash
> >   $ bash -c 'echo SHELL: $SHELL'  # does this prove SHELL is exported?
> >   SHELL: /bin/bash
> 
> No.  And in fact, bash does not export SHELL by default, but defaults to
> defining SHELL as a shell-local variable.  You have to explicitly export
> it yourself if you want child processes to see it.

OK. Thanks, good to know that.

--
Still, not sure why I have to export the SHELL var to GNU screen
now since in the past several years I have not done this.
Recently I stopped using 'putty -ssh localhost' for my terminal,
and I'm using 'rxvt' instead, but I can not see why that would
matter.  In Linux, 'screen' sets up login shells correctly, I
use the same ~/.screenrc for both cygwin and linux, and I'm not
exporting SHELL to screen in linux.

Non cygwin question: what is the best way to tell GNU screen to
read /etc/passwd to get SHELL, and start all new screen windows
with login shells?

--
thanks,
Tom



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Re: GNU screen not seeing $SHELL env var?

[Corinna Vinschen]

On Jun 20 09:53, Tom Rodman wrote:
> On Wed 6/20/12 8:07 MDT Eric Blake wrote:
> > On 06/20/2012 07:20 AM, Tom Rodman wrote:
> > 
> > >   $ echo $SHELL
> > >   /bin/bash
> > >   $ bash -c 'echo SHELL: $SHELL'  # does this prove SHELL is exported?
> > >   SHELL: /bin/bash
> > 
> > No.  And in fact, bash does not export SHELL by default, but defaults to
> > defining SHELL as a shell-local variable.  You have to explicitly export
> > it yourself if you want child processes to see it.
> 
> OK. Thanks, good to know that.
> 
> --
> Still, not sure why I have to export the SHELL var to GNU screen
> now since in the past several years I have not done this.
> Recently I stopped using 'putty -ssh localhost' for my terminal,
> and I'm using 'rxvt' instead, ...

Brr.  Why don't you use mintty instead?  rxvt is old, unmaintained,
and it doesn't support UTF-8.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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Re: GNU screen not seeing $SHELL env var?

[Tom Rodman]

On Wed 6/20/12 17:24 +0200 Corinna wrote:
> On Jun 20 09:53, Tom Rodman wrote:
> > On Wed 6/20/12 8:07 MDT Eric Blake wrote:
> > > On 06/20/2012 07:20 AM, Tom Rodman wrote:
> > > 
> > > >   $ echo $SHELL
> > > >   /bin/bash
> > > >   $ bash -c 'echo SHELL: $SHELL'  # does this prove SHELL is exported?
> > > >   SHELL: /bin/bash
> > > 
> > > No.  And in fact, bash does not export SHELL by default, but defaults to
> > > defining SHELL as a shell-local variable.  You have to explicitly export
> > > it yourself if you want child processes to see it.
> > 
> > OK. Thanks, good to know that.
> > 
> > --
> > Still, not sure why I have to export the SHELL var to GNU screen
> > now since in the past several years I have not done this.
> > Recently I stopped using 'putty -ssh localhost' for my terminal,
> > and I'm using 'rxvt' instead, ...
> 
> Brr.  Why don't you use mintty instead?  rxvt is old, unmaintained,
> and it doesn't support UTF-8.

Oh, I was afraid it might be deprecated, I had tried mintty in the
last few weeks, but was unable to get 'WordChars' setting to work
as well as rxvt's cutchars.

I launch rxvt with a shell script using:

  font_sz=${1:-17}

  cutchars=$'\140'$'\042'$'\047''+-&()*,;<=>?@[]{|}/.:'
    # \140 == `
    # \042 == "
    # \047 == '

    # "Rxvt*cutchars" in ~/.Xdefaults ( usually a link to /etc/skel/.Xdefaults )
    #    but stopped working for me, 1st noticed not working in 2012 or 2011

  exec rxvt \
    -cutchars  $cutchars \
    -backspacekey $'\010' -geometry 100x33 \
    +rv \
    -bg black \
    -fg white \
    -fn "Lucida Console-$font_sz"  \
    -sr -sl 5000 \
    -e /bin/bash --login

I've been unable to get the equivalent of cutchars to work in mintty.
Putty was good at that, but I stopped using putty because of the 'procps' hangs.

--
Tom

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