# If a user goes from the homepage 'index.pl' to 'search.pl'
$ENV{'HTTP_REFERER'} =~ /index.pl/;

# From 'search.pl', a user clicks on the link to login via 'login.pl'
$ENV{'HTTP_REFERER'} =~ /search.pl/;

# If the user logs in SUCCESSFULLY they are redirected
# back to 'search.pl'
#
# However, if the user types an incorrect password,
# $ENV{'HTTP_REFERER'} matches
# $ENV{'HTTP_REFERER'} =~ /login.pl/ instead of retaining the
# intended $ENV{'HTTP_REFERER'} =~ /search.pl/