What Is CGI.pm?

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∟What Is CGI.pm?

This section describes what is CGI.pm - a Perl module that helps you to process HTTP requests and prepare HTTP responses through the CGI (Common Gateway Interface) standard.

What Is CGI.pm? CGI.pm, developed by Lincoln D. Stein, is a Perl module that helps you to process HTTP requests and prepare HTTP responses through the CGI (Common Gateway Interface) standard.

The current version of CGI.pm included in Perl 5.18 support a large number of properties and methods, which can be divided into these categories:

1. Constructing Query Objects - Methods to construct query (CGI) object to represent HTTP requests.

$q = CGI->new() - Create a query (CGI) object that represents the HTTP request provided by the CGI interface.
$q = CGI->new(INPUTFILE) - Create a query (CGI) object that represents a HTTP request described by the specified input file. This constructor is usually used for debugging purpose.

2. Managing Parameters from Request - Methods to manage parameters provided in the HTTP request.

@l = $q->param() - Return parameter names as an array from the current query object.
$v = $q->param{$n} - Return the parameter value of the specified parameter name from the current query object.
$q->param{$n, $v} - Add a new parameter to the current query object.
$q->delete{$n} - Delete a parameter from the current query object.

3. Retrieving Headers from Request - Methods to retrieve header line information from the HTTP request.

@l = $q->http() - Return header names as an array from the HTTP request
$v = $q->http($n) - Return the header value of the given header name from the HTTP request.
$v = $q->accept() - Return the "Accept:" header value from the HTTP request.
$v = $q->user_agent() - Return the "User-Agent:" header value from the HTTP request.
$v = $q->content_type() - Return the "Content-Type:" header value from the HTTP request.
$v = $q->request_method() - Return the method of the HTTP request: GET, POST, ...
$v = $q->raw_cookie() - Return cookies from the HTTP request in raw format.
$v = $q->referer() - Return the "Referer:" header value from the HTTP request.
...

4. Retrieving Server information - Methods to retrieve environment information from the Web server.

$v = $q->path_info() - Return the path name from the URI that invokes this CGI script.
$v = $q->path_translated() - Return the physical path name of this CGI script file.
$v = $q->script_name() - Return the file name of this CGI script file.
$v = $q->remote_host() - Return the remote host name.
$v = $q->remote_addr() - Return the remote host IP address.
$v = $q->server_name() - Return the host name of the Web server.
$v = $q->server_port() - Return the port number used by the Web server.
$v = $q->url() - Return the current URI without query string.
$v = $q->url(-query=>1) - Return the current URI with query string.
...

5. Setting Headers to Response - Methods to create header lines ready to be printed to the HTTP response.

print $q->header() - Print the default header line "Content-Type: text/html; charset=ISO-8859-1". Note that header() should only be called once.
print $q->header('image/gif') - Print the default header line with "image/gif" as the content type.
print $q->header(-status=>'402 Payment required', -type=>'image/gif', -charset=>'utf8', ...) - Print header lines with give header names and values.
print $q->redirect($uri); - Print a redirect header to the HTTP response with the default redirect status "302 Found", meaning moved temporarily.
print $q->redirect(-uri=>$uri, -status=>$s); - Print a redirect header to the HTTP response.

6. Building Response Content - Methods to build HTML elements ready to be printed to the HTTP response.

print $q->start_html() - Print default <html>, <head> and <body> elements.
print $q->start_html(-title=>'...', -meta=>'...', -style=>'...', ...) - Print <html>, <head> and <body> elements with sub elements like <title>, <meta>, <style>, ...
print $q->end_html() - Print default ending tags: </html> and </html> .
print $q->h1('...') - Print a <h1> element.
print $q->p('...') - Print a <p> element.
print $q->pre('...') - Print a <pre> element.
print $q->hr() - Print a <hr> element.
print $q->a(-href=>'...', '...') - Print a <a> element.
print $q->img(-src=>'...') - Print a <img> element.
...