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ISBN : 978-2-7460-9712-4
EAN : 9782746097124
(Editions ENI)


CentOS 2.1AS







LWP: :UserAgent − A WWW UserAgent class


 require LWP::UserAgent;
 $ua = LWP::UserAgent->new;
 $request = HTTP::Request->new(’GET’, ’file://localhost/etc/motd’);
 $response = $ua->request($request); # or
 $response = $ua->request($request, ’/tmp/sss’); # or
 $response = $ua->request($request, \&callback, 4096);

 sub callback { my($data, $response, $protocol) = @_; .... }


The "LWP::UserAgent" is a class implementing a simple World-Wide Web user agent in Perl. It brings together the HTTP: :Request, HTTP: :Response and the LWP: :Protocol classes that form the rest of the core of libwww-perl library. For simple uses this class can be used directly to dispatch WWW requests, alternatively it can be subclassed for application-specific behaviour.

In normal use the application creates a UserAgent object, and then configures it with values for timeouts, proxies, name, etc. It next creates an instance of "HTTP::Request" for the request that needs to be performed. This request is then passed to the UserAgent request() method, which dispatches it using the relevant protocol, and returns a "HTTP::Response" object.

The basic approach of the library is to use HTTP style communication for all protocol schemes, i.e. you also receive an "HTTP::Response" object for gopher or ftp requests. In order to achieve even more similarity to HTTP style communications, gopher menus and file directories are converted to HTML documents.

The request() method can process the content of the response in one of three ways: in core, into a file, or into repeated calls to a subroutine. You choose which one by the kind of value passed as the second argument to request().

The in core variant simply stores the content in a scalar ’content’ attribute of the response object and is suitable for small HTML replies that might need further parsing. This variant is used if the second argument is missing (or is undef).

The filename variant requires a scalar containing a filename as the second argument to request() and is suitable for large WWW objects which need to be written directly to the file without requiring large amounts of memory. In this case the response object returned from request() will have an empty content attribute. If the request fails, then the content might not be empty, and the file will be untouched.

The subroutine variant requires a reference to callback routine as the second argument to request() and it can also take an optional chuck size as the third argument. This variant can be used to construct "pipe-lined" processing, where processing of received chuncks can begin before the complete data has arrived. The callback function is called with 3 arguments: the data received this time, a reference to the response object and a reference to the protocol object. The response object returned from request() will have empty content. If the request fails, then the the callback routine is not called, and the response->content might not be empty.

The request can be aborted by calling die() in the callback routine. The die message will be available as the "X-Died" special response header field.

The library also allows you to use a subroutine reference as content in the request object. This subroutine should return the content (possibly in pieces) when called. It should return an empty string when there is no more content.


The following methods are available:
$ua =
LWP: :UserAgent->new;

Constructor for the UserAgent. Returns a reference to a LWP: :UserAgent object.

$ua->simple_request($request, [$arg [, $size]])

This method dispatches a single WWW request on behalf of a user, and returns the response received. The "$request" should be a reference to a "HTTP::Request" object with values defined for at least the method() and uri() attributes.

If "$arg" is a scalar it is taken as a filename where the content of the response is stored.

If "$arg" is a reference to a subroutine, then this routine is called as chunks of the content is received. An optional "$size" argument is taken as a hint for an appropriate chunk size.

If "$arg" is omitted, then the content is stored in the response object itself.

$ua->request($request, $arg [, $size])

Process a request, including redirects and security. This method may actually send several different simple requests.

The arguments are the same as for "simple_request()".


This method is called by request() before it tries to do any redirects. It should return a true value if a redirect is allowed to be performed. Subclasses might want to override this.

The default implementation will return FALSE for POST request and TRUE for all others.

$ua->credentials($netloc, $realm, $uname, $pass)

Set the user name and password to be used for a realm. It is often more useful to specialize the get_basic_credentials() method instead.

$ua->get_basic_credentials($realm, $uri, [$proxy])

This is called by request() to retrieve credentials for a Realm protected by Basic Authentication or Digest Authentication.

Should return username and password in a list. Return undef to abort the authentication resolution atempts.

This implementation simply checks a set of pre-stored member variables. Subclasses can override this method to e.g. ask the user for a username/password. An example of this can be found in "lwp−request" program distributed with this library.


Get/set the product token that is used to identify the user agent on the network. The agent value is sent as the "User-Agent" header in the requests. The default agent name is "libwww-perl/#.##", where "#.##" is substitued with the version numer of this library.

The user agent string should be one or more simple product identifiers with an optional version number separated by the "/" character. Examples are:

  $ua->agent(’Checkbot/0.4 ’ . $ua->agent);


Get/set the Internet e-mail address for the human user who controls the requesting user agent. The address should be machine-usable, as defined in RFC 822. The from value is send as the "From" header in the requests. There is no default. Example:



Get/set the timeout value in seconds. The default timeout() value is 180 seconds, i.e. 3 minutes.


Get/set the HTTP: :Cookies object to use. The default is to have no cookie_jar, i.e. never automatically add "Cookie" headers to the requests.


Get/set a value indicating wether we should initialize response headers from the <head> section of HTML documents. The default is TRUE . Do not turn this off, unless you know what you are doing.


Get/set the size limit for response content. The default is undef, which means that there is no limit. If the returned response content is only partial, because the size limit was exceeded, then a "X-Content-Range" header will be added to the response.


Returns a copy of the LWP: :UserAgent object


You can use this method to query if the library currently support the specified "scheme". The "scheme" might be a string (like ’http’ or ’ftp’) or it might be an URI object reference.

$ua->mirror($url, $file)

Get and store a document identified by a URL , using If-Modified-Since, and checking of the Content-Length. Returns a reference to the response object.


Set/retrieve proxy URL for a scheme:

 $ua->proxy([’http’, ’ftp’], ’http://proxy.sn.no:8001/’);
 $ua->proxy(’gopher’, ’http://proxy.sn.no:8001/’);

The first form specifies that the URL is to be used for proxying of access methods listed in the list in the first method argument, i.e. ’http’ and ’ftp’.

The second form shows a shorthand form for specifying proxy URL for a single access scheme.


Load proxy settings from *_proxy environment variables. You might specify proxies like this (sh-syntax):

  export gopher_proxy wais_proxy no_proxy

Csh or tcsh users should use the "setenv" command to define these environment variables.

On systems with case-insensitive environment variables there exists a name clash between the CGI environment variables and the "HTTP_PROXY" environment variable normally picked up by env_proxy(). Because of this "HTTP_PROXY" is not honored for CGI scripts. The "CGI_HTTP_PROXY" environment variable can be used instead.


Do not proxy requests to the given domains. Calling no_proxy without any domains clears the list of domains. Eg:

 $ua->no_proxy(’localhost’, ’no’, ...);


See the LWP manpage for a complete overview of libwww-perl5. See lwp-request and lwp-mirror for examples of usage.


Copyright 1995−2000 Gisle Aas.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.