%ENV is already uppercase only, 
C:\>perl -le"$ENV{lowerlowerlower}=1;print for keys %ENV"
USERPROFILE
HOMEDRIVE
CLIENTNAME
COMMONPROGRAMFILES
APPDATA
PROGRAMFILES
OS
PATHEXT
PROMPT
NUMBER_OF_PROCESSORS
HOMEPATH
PATH
USERDOMAIN
PROCESSOR_ARCHITECTURE
TEMP
SYSTEMDRIVE
COMSPEC
WINDIR
PROCESSOR_LEVEL
USERNAME
LOWERLOWERLOWER
PROCESSOR_IDENTIFIER
ALLUSERSPROFILE
COMPUTERNAME

C:\>

[download]
Don't count on a specific environment variable existing in %ENV. Don't count on %ENV entries being case-sensitive, or even case-preserving. Don't try to clear %ENV by saying "%ENV = ();", or, if you really have to, make it conditional on "$^O ne 'VMS'" since in VMS the %ENV table is much more than a per-process key-value string table.

In reply to Re: Case insensitive keys in global %ENV by Anonymous Monk
in thread Case insensitive keys in global %ENV by bdimych

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