win32utils devel - Mar 2008 - GetTempPath vs GetEnvironmentVariable vs getenv

Hi all,
 
I discovered some interesting quirks with regards to getting environment
variable information on Windows. It''s because ''TMP''
is considered a
system environment variable, which you can''t change with
SetEnvironmentVariable() according to the docs.
 
I also noticed that GetTempPath() returns a full path if you set the
value to a relative path.
 
Here''s a little program that demonstrates what I''m talking
about:
 
# Compare getenv/putenv, GetEnvironmentVariable/SetEnvironmentVariable
require ''windows/api''
include Windows
 
GetTempPath =
API.new(''GetTempPath'',''LP'',''L'')
 
GetEnvironmentVariable = API.new(''GetEnvironmentVariable'',
''PPL'', ''L'')
SetEnvironmentVariable = API.new(''SetEnvironmentVariable'',
''PP'', ''B'')
 
Getenv = API.new(''getenv'', ''P'',
''P'', ''msvcrt'')
Putenv = API.new(''_putenv'', ''P'',
''I'', ''msvcrt'')
 
# ENV
def get_env1(var)
   ENV[var]
end
 
# GetEnvironmentVariable
def get_env2(var)
   buf = 0.chr * 260
   GetEnvironmentVariable.call(''TMP'', buf, buf.length)
   buf.unpack(''A*'').first
end
  
# GetTempPath, which looks for ''TMP'' first
def get_env3
   buf = 0.chr * 260
   GetTempPath.call(buf.length, buf)
   buf.unpack(''A*'').first
end
 
# getenv()
def get_env4(var)
   Getenv.call(var)
end
 
puts get_env1(''TMP'') # C:\DOCUME~1\djberge\LOCALS~1\Temp
puts get_env2(''TMP'') # C:\DOCUME~1\djberge\LOCALS~1\Temp
puts get_env3        # C:\DOCUME~1\djberge\LOCALS~1\Temp\
puts get_env4(''TMP'') # C:\DOCUME~1\djberge\LOCALS~1\Temp
 
# Set ''TMP'' using Ruby''s
ENV[]ENV[''TMP''] = "C:\\foo\\bar"
puts "=" * 40
 
puts get_env1(''TMP'') # C:\foo\bar
puts get_env2(''TMP'') # C:\foo\bar
puts get_env3        # C:\foo\bar\
puts get_env4(''TMP'') # C:\DOCUME~1\djberge\LOCALS~1\Temp -
oops
 
# Set ''TMP'' using SetEnvironmentVariable
SetEnvironmentVariable.call(''TMP'', "C:\\zap")
puts "=" * 40
 
puts get_env1(''TMP'') # C:\zap
puts get_env2(''TMP'') # C:\zap
puts get_env3        # C:\zap\
puts get_env4(''TMP'') # C:\DOCUME~1\djberge\LOCALS~1\Temp -
oops
 
# Set ''TMP'' using putenv
Putenv.call("TMP=C:\\blah")
puts "=" * 40
 
puts get_env1(''TMP'') # C:\blah
puts get_env2(''TMP'') # C:\blah
puts get_env3        # C:\blah\
puts get_env4(''TMP'') # C:\blah - ah, there we go
 
# Set ''TMP'' to a relative path
Putenv.call("TMP=dan")
puts "=" * 40
 
puts get_env1(''TMP'') # dan
puts get_env2(''TMP'') # dan
puts get_env3        # C:\Documents and Settings\djberge\My
Documents\dan - full
puts get_env4(''TMP'') # dan

The odd thing about TMP is that my shell value doesn''t match the
registry setting. The ''set'' output shows:
 
TMP=C:\DOCUME~1\djberge\LOCALS~1\Temp
 
But the registry entry, under
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session
Manager\Environment, is set to:
 
C:\Temp
 
Anyway, just thought I''d share.
 
Regards,
 
Dan


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Hi,

2008/3/25, Berger, Daniel <Daniel.Berger at qwest.com>:
>  Hi all,
>
> I discovered some interesting quirks with regards to getting environment
> variable information on Windows. It''s because
''TMP'' is considered a system
> environment variable, which you can''t change with
SetEnvironmentVariable()
> according to the docs.
>
I don''t think so. ''TMP'' can be changed with
SetEnvironmentVariable().
But it affected only the current running process and child processes.
Environment variable can be categorized into three levels: process, user and
system level.
You can change user and System environment variable persistently via
registry setting.


>  The odd thing about TMP is that my shell value doesn''t match the
registry
> setting. The ''set'' output shows:
>
> TMP=C:\DOCUME~1\djberge\LOCALS~1\Temp
>
> But the registry entry, under
> HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session
> Manager\Environment, is set to:
>
> C:\Temp
>

User environment variables are stored in the Registry in the key:

HKEY_CURRENT_USER\Environment

System variables are found in the key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session
Manager\Environment

Refer to http://vlaurie.com/computers2/Articles/environment.htm

Regards,

Park Heesob
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