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In-Reply-To: <824c5748-594e-cf7c-4bba-4b70f9f593b1@cs.umass.edu>
Date: Sat, 5 Sep 2020 11:57:05 -0500
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Subject: Re: Is this a bug in bash?
To: moss@cs.umass.edu
From: Greg Borbonus via Cygwin <cygwin@cygwin.com>
Reply-To: Greg Borbonus <gregborbonus@gmail.com>
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Yeah, thought the expansion might be causing the issue.

Thanks,
Greg Borbonus

On Sat, Sep 5, 2020, 10:44 AM Eliot Moss <moss@cs.umass.edu> wrote:

> On 9/5/2020 11:29 AM, Greg Borbonus via Cygwin wrote:
>  > Out of curiosity, why are there 2 different sets of quotes?
>  >
>  > Thanks,
>  > Greg Borbonus
>  >
>  > On Fri, Sep 4, 2020, 10:23 PM Bob McGowan via Cygwin <cygwin@cygwin.com
> >
>  > wrote:
>  >
>  >> I am trying to set things up so the Bash profile detects if bash is
>  >> running from the Windows "XWin Server" startup link or not. The startup
>  >> link has the following as the command:
>  >>
>  >> C:\cygwin64\bin\run.exe --quote /usr/bin/bash.exe -l -c "cd; exec
>  >> /usr/bin/startxwin"
>  >>
>  >> So I thought I'd try adding the env command to set an environment
> variable:
>  >>
>  >> C:\cygwin64\bin\run.exe --quote /usr/bin/env startxwin=yes
>  >> /usr/bin/bash.exe -l -c "cd; exec /usr/bin/startxwin"
>  >>
>  >> This works (if there's a better way, I'd be happy to learn of it) but
> in
>  >> the process of testing I had a problem when echo'ing the variable.
>  >>
>  >> For purposes of describing the bug, I simplified the command as
> follows:
>  >>
>  >>       env startup=yes bash -l -c 'echo "cmd:  $startup"'
>  >>
>  >> I also added an "echo profile: $startup" to the .bash_profile file.
>  >>
>  >> When I run the above in a Cygwin shell, the output is:
>  >>
>  >> $ env startup=yes bash -l -c "echo cmd: $startup"
>  >> profile: yes
>  >> $
>  >>
>  >> When I run it in a Linux shell, the output is:
>  >>
>  >> $ env startup=yes bash -l -c 'echo "cmd:  $startup"'
>  >> profile: yes
>  >> cmd:  yes
>  >> $
>  >>
>  >> As you can see, the Cygwin side fails to generate any output from the
> -c
>  >> echo command but on the Linux system there is output.
>  >>
>  >> Normally I'd call this a bug but since this is running under Windows it
>  >> may be some weirdness of the implementation required to create the
> Linux
>  >> like environment.
>  >>
>  >> The Bash version in Cygwin is  4.4.12(3)-release and for my Debian
> Linux
>  >> system, it is 5.0.3(1)-release.  So it could also be that it existed in
>  >> Linux 4.x series and has been fixed in the 5.x series.
>
> The inner quotes are necessary because there are two spaces beween cmd: and
> $startup, and the : may be risky unquoted in bash (actually it is ok, but I
> try to be careful about anything not a letter or digit, etc.).  The outer
> ones
> are single quotes, which protect $startup from being expanded before it
> gets
> to the new bash.  " " (double) quotes do not prevent $ expansion.  (You
> want
> the new bash to do the expansion.)  However, I think this would also work:
>
>      env startup=yes bash -l -c echo 'cmd:  $startup'
>
> Regards - Eliot Moss
>
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