$ENV{VARIABLE} = '/base/path';
$_ = '$ENV{VARIABLE}/my/path';

s/\$ENV\{(\w+?)\}/$ENV{$1}/g;
print;

##</code><code>##

$ENV{VARIABLE} = '/base/path';
$path = 'path';
$_ = '$ENV{VARIABLE}/my/$path';

s/\$(\w+)\{(\w+?)\}/${$1}{$2}/g;
s/\$(\w+)/${$1}/g;
print;