Re: Is this a bug in bash?

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

On 9/5/2020 3:18 PM, Bob McGowan wrote:
> On 9/5/2020 8:44 AM, Eliot Moss 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
> 
> Actually this won't work, because the -c option to bash only takes one argument, so in this case 
> bash would execute the 'echo', you'd get a blank line, and the rest would be ignored.
> 
> You need to put the first single quote before the echo command:
> 
>      env startup=yes bash -l -c 'echo cmd:  $startup'
> 
> I put in the second set of quote entirely because of the double space after the colon.  I just like 
> to be grammatically correct ;) but as you say, they are not relevant to the actual execution of the 
> command.
> 
> And for the command stored in the Windows shortcut, there are no colons or variables, so only one 
> set of quotes need to be used. And I believe Windows only cares about double quotes so they are used 
> here:
> 
>      C:\cygwin64\bin\run.exe --quote /usr/bin/env startxwin=yes /usr/bin/bash.exe -l -c "cd; exec 
> /usr/bin/startxwin"
> 
> Apologies for any confusion this may have caused.

Quote right that the -c command needs to be quoted with all of its arguments!  EM