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Subject: Re: Is this a bug in bash?
To: Greg Borbonus <gregborbonus AT gmail DOT com>, Bob McGowan <ramjr0915 AT gmail DOT com>
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From: Eliot Moss <moss AT cs DOT umass DOT edu>
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Date: Sat, 5 Sep 2020 11:44:37 -0400
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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 AT cygwin DOT 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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