perl -e 'print "Output:\n"; for $i (1..3) {
 print "$i: ".(defined($_)? "defined\n":"not defined\n");
 $_ = ($i==1) ? "":undef
 }'
Output:
1: not defined
2: defined
3: not defined

##</code><code>##

open( STDERR, ">", \$stderr_log );