Just specify which environment variable(s) you wish to use:

use strict;
use warnings;
use Env qw/EGGSHELL/;
                                                                      
+          
if (defined $EGGSHELL) {
    print "$EGGSHELL\n";
} else {
    print "EGGSHELL not defined in \%ENV\n";
}
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And then (for example):

[liverpole@golux ~]% perl envtest
EGGSHELL not defined in %ENV
[liverpole@golux ~]% setenv EGGSHELL 1379
[liverpole@golux ~]% perl envtest
1379
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