Re: Is this a bug in bash?

[Eliot Moss <moss@cs.umass.edu>]

On 9/5/2020 12:57 PM, Greg Borbonus wrote:
> 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 <mailto: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
>     <mailto: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'

Please put responses at the bottom ("Don't top post") on this list.

I wasn't saying the quotes were a problem, only explaining to a correspondent why they might be 
necessary, etc.

EM