Cygwin versus MinGW/MSYS - differing behavior of 'export -p'

[Tim Bell]

All -

I have been working on getting build-infra/common/bin/extractvcvars.sh 
working under MSYS. extractvcvars.sh runs vcvarsall.bat[1] to find the 
VStudio tools.  It does this by writing and executing a small .bat file 
that runs 'bash -c export -p' before and after vcvarsall.bat, then 
diffing the output.


If you open a Cygwin window and run 'bash -c export -p' you get a list 
of all your environment variables, for example:

% bash -c export -p | sort -f
declare -x !C:
declare -x _="/usr/bin/bash"
   [... snip ...]
declare -x TEMP="/tmp"
declare -x temp="C:\\Users\\tbbell\\AppData\\Local\\Temp"
declare -x TERM="cygwin"
declare -x TMP="/tmp"
declare -x tmp="C:\\Users\\tbbell\\AppData\\Local\\Temp"
declare -x TMPDIR="/cygdrive/c/Users/tbbell/AppData/Local/Temp"

Note the upper/lower case environment variables listed.


If you run the MSYS bash in the same window (same environment):

% /cygdrive/c/jprt/products/P1/MinGW/msys/1.0/bin/bash -c export -p | 
sort -f
declare -x !C:="C:\\cygwin\\bin"
declare -x _="/cygdrive/c/jprt/products/P1/MinGW/msys/1.0/bin/bash"
   [... snip ...]
declare -x TEMP="/tmp"
declare -x TERM="cygwin"
declare -x TMP="/tmp"
declare -x TMPDIR="/tmp"

Notice we get back only upper case environment variables.  In the case 
of TMP versus tmp and TEMP versus temp, the uppercase variable wins.

I don't think this behavior will affect the project, and I plan to move 
forward tomorrow.  Yet I find the difference somewhat startling, and it 
will be something to look out for.

Tim

[1] located here on my Windows 7 development system:
c:/Program Files (x86)/Microsoft Visual Studio 
10.0/Common7/Tools/../../VC/vcvarsall.bat