How can I determine if a script was called from the command line or as a cgi script?

Question

I have a script that I wrote that can either be used on the command line or as a CGI script, and need to determine how the script was called so I can output a content-type h

Answer 1

I usually do a little trick at the beginning of my module:

exit run(@ARGV) unless caller();   # run directly if called from command line

sub run
{
    process_options(@_);
    ...
}

sub process_options {
    @ARGV = @_;
    my  %opts;
    GetOptions(\%opts,
    ...
}

The module does not have to be named "run".