Retrieving Form Data
Several environment variables are set up by the server to pass information about the request to the Perl script.
If the form data was sent using a GET request, the most important is QUERY_STRING, which contains all the text in the URL following the first ? character.
If the form data was sent using a POST request, the environment variable CONTENT_LENGTH contains the length in bytes of the posted data. To retrieve this data, these bytes are read from the standard input of the script.