I tend to write CGI scripts in a c-ish manner, so there'll be a sub for each page-output & often some support subs, then main() comes down to an if statement on 1 parameter:

## main foo starts
my $run = param("run");
if ($run eq 'sub_1') {
    sub_1;
} elsif ($run eq 'sub_2') {
    sub_2;
} else {
    start_page
}
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Very handy for testing as I can then call each sub individually.