path: root/README.md

# NAME

URI - Uniform Resource Identifiers (absolute and relative)

# SYNOPSIS

    use URI ();

    $u1 = URI->new("http://www.example.com");
    $u2 = URI->new("foo", "http");
    $u3 = $u2->abs($u1);
    $u4 = $u3->clone;
    $u5 = URI->new("HTTP://WWW.example.com:80")->canonical;

    $str = $u->as_string;
    $str = "$u";

    $scheme = $u->scheme;
    $opaque = $u->opaque;
    $path   = $u->path;
    $frag   = $u->fragment;

    $u->scheme("ftp");
    $u->host("ftp.example.com");
    $u->path("cpan/");

# DESCRIPTION

This module implements the `URI` class.  Objects of this class
represent "Uniform Resource Identifier references" as specified in RFC
2396 (and updated by RFC 2732).

A Uniform Resource Identifier is a compact string of characters that
identifies an abstract or physical resource.  A Uniform Resource
Identifier can be further classified as either a Uniform Resource Locator
(URL) or a Uniform Resource Name (URN).  The distinction between URL
and URN does not matter to the `URI` class interface. A
"URI-reference" is a URI that may have additional information attached
in the form of a fragment identifier.

An absolute URI reference consists of three parts:  a _scheme_, a
_scheme-specific part_ and a _fragment_ identifier.  A subset of URI
references share a common syntax for hierarchical namespaces.  For
these, the scheme-specific part is further broken down into
_authority_, _path_ and _query_ components.  These URIs can also
take the form of relative URI references, where the scheme (and
usually also the authority) component is missing, but implied by the
context of the URI reference.  The three forms of URI reference
syntax are summarized as follows:

    <scheme>:<scheme-specific-part>#<fragment>
    <scheme>://<authority><path>?<query>#<fragment>
    <path>?<query>#<fragment>

The components into which a URI reference can be divided depend on the
_scheme_.  The `URI` class provides methods to get and set the
individual components.  The methods available for a specific
`URI` object depend on the scheme.

# CONSTRUCTORS

The following methods construct new `URI` objects:

- $uri = URI->new( $str )
- $uri = URI->new( $str, $scheme )

    Constructs a new URI object.  The string
    representation of a URI is given as argument, together with an optional
    scheme specification.  Common URI wrappers like "" and <>, as well as
    leading and trailing white space, are automatically removed from
    the $str argument before it is processed further.

    The constructor determines the scheme, maps this to an appropriate
    URI subclass, constructs a new object of that class and returns it.

    If the scheme isn't one of those that URI recognizes, you still get
    an URI object back that you can access the generic methods on.  The
    `$uri->has_recognized_scheme` method can be used to test for
    this.

    The $scheme argument is only used when $str is a
    relative URI.  It can be either a simple string that
    denotes the scheme, a string containing an absolute URI reference, or
    an absolute `URI` object.  If no $scheme is specified for a relative
    URI $str, then $str is simply treated as a generic URI (no scheme-specific
    methods available).

    The set of characters available for building URI references is
    restricted (see [URI::Escape](https://metacpan.org/pod/URI%3A%3AEscape)).  Characters outside this set are
    automatically escaped by the URI constructor.

- $uri = URI->new\_abs( $str, $base\_uri )

    Constructs a new absolute URI object.  The $str argument can
    denote a relative or absolute URI.  If relative, then it is
    absolutized using $base\_uri as base. The $base\_uri must be an absolute
    URI.

- $uri = URI::file->new( $filename )
- $uri = URI::file->new( $filename, $os )

    Constructs a new _file_ URI from a file name.  See [URI::file](https://metacpan.org/pod/URI%3A%3Afile).

- $uri = URI::file->new\_abs( $filename )
- $uri = URI::file->new\_abs( $filename, $os )

    Constructs a new absolute _file_ URI from a file name.  See
    [URI::file](https://metacpan.org/pod/URI%3A%3Afile).

- $uri = URI::file->cwd

    Returns the current working directory as a _file_ URI.  See
    [URI::file](https://metacpan.org/pod/URI%3A%3Afile).

- $uri->clone

    Returns a copy of the $uri.

# COMMON METHODS

The methods described in this section are available for all `URI`
objects.

Methods that give access to components of a URI always return the
old value of the component.  The value returned is `undef` if the
component was not present.  There is generally a difference between a
component that is empty (represented as `""`) and a component that is
missing (represented as `undef`).  If an accessor method is given an
argument, it updates the corresponding component in addition to
returning the old value of the component.  Passing an undefined
argument removes the component (if possible).  The description of
each accessor method indicates whether the component is passed as
an escaped (percent-encoded) or an unescaped string.  A component that can be further
divided into sub-parts are usually passed escaped, as unescaping might
change its semantics.

The common methods available for all URI are:

- $uri->scheme
- $uri->scheme( $new\_scheme )

    Sets and returns the scheme part of the $uri.  If the $uri is
    relative, then $uri->scheme returns `undef`.  If called with an
    argument, it updates the scheme of $uri, possibly changing the
    class of $uri, and returns the old scheme value.  The method croaks
    if the new scheme name is illegal; a scheme name must begin with a
    letter and must consist of only US-ASCII letters, numbers, and a few
    special marks: ".", "+", "-".  This restriction effectively means
    that the scheme must be passed unescaped.  Passing an undefined
    argument to the scheme method makes the URI relative (if possible).

    Letter case does not matter for scheme names.  The string
    returned by $uri->scheme is always lowercase.  If you want the scheme
    just as it was written in the URI in its original case,
    you can use the $uri->\_scheme method instead.

- $uri->has\_recognized\_scheme

    Returns TRUE if the URI scheme is one that URI recognizes.

    It will also be TRUE for relative URLs where a recognized
    scheme was provided to the constructor, even if `$uri->scheme`
    returns `undef` for these.

- $uri->opaque
- $uri->opaque( $new\_opaque )

    Sets and returns the scheme-specific part of the $uri
    (everything between the scheme and the fragment)
    as an escaped string.

- $uri->path
- $uri->path( $new\_path )

    Sets and returns the same value as $uri->opaque unless the URI
    supports the generic syntax for hierarchical namespaces.
    In that case the generic method is overridden to set and return
    the part of the URI between the _host name_ and the _fragment_.

- $uri->fragment
- $uri->fragment( $new\_frag )

    Returns the fragment identifier of a URI reference
    as an escaped string.

- $uri->as\_string

    Returns a URI object to a plain ASCII string.  URI objects are
    also converted to plain strings automatically by overloading.  This
    means that $uri objects can be used as plain strings in most Perl
    constructs.

- $uri->as\_iri

    Returns a Unicode string representing the URI.  Escaped UTF-8 sequences
    representing non-ASCII characters are turned into their corresponding Unicode
    code point.

- $uri->canonical

    Returns a normalized version of the URI.  The rules
    for normalization are scheme-dependent.  They usually involve
    lowercasing the scheme and Internet host name components,
    removing the explicit port specification if it matches the default port,
    uppercasing all escape sequences, and unescaping octets that can be
    better represented as plain characters.

    For efficiency reasons, if the $uri is already in normalized form,
    then a reference to it is returned instead of a copy.

- $uri->eq( $other\_uri )
- URI::eq( $first\_uri, $other\_uri )

    Tests whether two URI references are equal.  URI references
    that normalize to the same string are considered equal.  The method
    can also be used as a plain function which can also test two string
    arguments.

    If you need to test whether two `URI` object references denote the
    same object, use the '==' operator.

- $uri->abs( $base\_uri )

    Returns an absolute URI reference.  If $uri is already
    absolute, then a reference to it is simply returned.  If the $uri
    is relative, then a new absolute URI is constructed by combining the
    $uri and the $base\_uri, and returned.

- $uri->rel( $base\_uri )

    Returns a relative URI reference if it is possible to
    make one that denotes the same resource relative to $base\_uri.
    If not, then $uri is simply returned.

- $uri->secure

    Returns a TRUE value if the URI is considered to point to a resource on
    a secure channel, such as an SSL or TLS encrypted one.

# GENERIC METHODS

The following methods are available to schemes that use the
common/generic syntax for hierarchical namespaces.  The descriptions of
schemes below indicate which these are.  Unrecognized schemes are
assumed to support the generic syntax, and therefore the following
methods:

- $uri->authority
- $uri->authority( $new\_authority )

    Sets and returns the escaped authority component
    of the $uri.

- $uri->path
- $uri->path( $new\_path )

    Sets and returns the escaped path component of
    the $uri (the part between the host name and the query or fragment).
    The path can never be undefined, but it can be the empty string.

- $uri->path\_query
- $uri->path\_query( $new\_path\_query )

    Sets and returns the escaped path and query
    components as a single entity.  The path and the query are
    separated by a "?" character, but the query can itself contain "?".

- $uri->path\_segments
- $uri->path\_segments( $segment, ... )

    Sets and returns the path.  In a scalar context, it returns
    the same value as $uri->path.  In a list context, it returns the
    unescaped path segments that make up the path.  Path segments that
    have parameters are returned as an anonymous array.  The first element
    is the unescaped path segment proper;  subsequent elements are escaped
    parameter strings.  Such an anonymous array uses overloading so it can
    be treated as a string too, but this string does not include the
    parameters.

    Note that absolute paths have the empty string as their first
    _path\_segment_, i.e. the _path_ `/foo/bar` have 3
    _path\_segments_; "", "foo" and "bar".

- $uri->query
- $uri->query( $new\_query )

    Sets and returns the escaped query component of
    the $uri.

- $uri->query\_form
- $uri->query\_form( $key1 => $val1, $key2 => $val2, ... )
- $uri->query\_form( $key1 => $val1, $key2 => $val2, ..., $delim )
- $uri->query\_form( \\@key\_value\_pairs )
- $uri->query\_form( \\@key\_value\_pairs, $delim )
- $uri->query\_form( \\%hash )
- $uri->query\_form( \\%hash, $delim )

    Sets and returns query components that use the
    _application/x-www-form-urlencoded_ format.  Key/value pairs are
    separated by "&", and the key is separated from the value by a "="
    character.

    The form can be set either by passing separate key/value pairs, or via
    an array or hash reference.  Passing an empty array or an empty hash
    removes the query component, whereas passing no arguments at all leaves
    the component unchanged.  The order of keys is undefined if a hash
    reference is passed.  The old value is always returned as a list of
    separate key/value pairs.  Assigning this list to a hash is unwise as
    the keys returned might repeat.

    The values passed when setting the form can be plain strings or
    references to arrays of strings.  Passing an array of values has the
    same effect as passing the key repeatedly with one value at a time.
    All the following statements have the same effect:

        $uri->query_form(foo => 1, foo => 2);
        $uri->query_form(foo => [1, 2]);
        $uri->query_form([ foo => 1, foo => 2 ]);
        $uri->query_form([ foo => [1, 2] ]);
        $uri->query_form({ foo => [1, 2] });

    The $delim parameter can be passed as ";" to force the key/value pairs
    to be delimited by ";" instead of "&" in the query string.  This
    practice is often recommended for URLs embedded in HTML or XML
    documents as this avoids the trouble of escaping the "&" character.
    You might also set the $URI::DEFAULT\_QUERY\_FORM\_DELIMITER variable to
    ";" for the same global effect.

- @keys = $u->query\_param
- @values = $u->query\_param( $key )
- $first\_value = $u->query\_param( $key )
- $u->query\_param( $key, $value,... )

    If $u->query\_param is called with no arguments, it returns all the
    distinct parameter keys of the URI.  In a scalar context it returns the
    number of distinct keys.

    When a $key argument is given, the method returns the parameter values with the
    given key.  In a scalar context, only the first parameter value is
    returned.

    If additional arguments are given, they are used to update successive
    parameters with the given key.  If any of the values provided are
    array references, then the array is dereferenced to get the actual
    values.

    Please note that you can supply multiple values to this method, but you cannot
    supply multiple keys.

    Do this:

        $uri->query_param( widget_id => 1, 5, 9 );

    Do NOT do this:

        $uri->query_param( widget_id => 1, frobnicator_id => 99 );

- $u->query\_param\_append($key, $value,...)

    Adds new parameters with the given
    key without touching any old parameters with the same key.  It
    can be explained as a more efficient version of:

        $u->query_param($key,
                        $u->query_param($key),
                        $value,...);

    One difference is that this expression would return the old values
    of $key, whereas the query\_param\_append() method does not.

- @values = $u->query\_param\_delete($key)
- $first\_value = $u->query\_param\_delete($key)

    Deletes all key/value pairs with the given key.
    The old values are returned.  In a scalar context, only the first value
    is returned.

    Using the query\_param\_delete() method is slightly more efficient than
    the equivalent:

        $u->query_param($key, []);

- $hashref = $u->query\_form\_hash
- $u->query\_form\_hash( \\%new\_form )

    Returns a reference to a hash that represents the
    query form's key/value pairs.  If a key occurs multiple times, then the hash
    value becomes an array reference.

    Note that sequence information is lost.  This means that:

        $u->query_form_hash($u->query_form_hash);

    is not necessarily a no-op, as it may reorder the key/value pairs.
    The values returned by the query\_param() method should stay the same
    though.

- $uri->query\_keywords
- $uri->query\_keywords( $keywords, ... )
- $uri->query\_keywords( \\@keywords )

    Sets and returns query components that use the
    keywords separated by "+" format.

    The keywords can be set either by passing separate keywords directly
    or by passing a reference to an array of keywords.  Passing an empty
    array removes the query component, whereas passing no arguments at
    all leaves the component unchanged.  The old value is always returned
    as a list of separate words.

# SERVER METHODS

For schemes where the _authority_ component denotes an Internet host,
the following methods are available in addition to the generic
methods.

- $uri->userinfo
- $uri->userinfo( $new\_userinfo )

    Sets and returns the escaped userinfo part of the
    authority component.

    For some schemes this is a user name and a password separated by
    a colon.  This practice is not recommended. Embedding passwords in
    clear text (such as URI) has proven to be a security risk in almost
    every case where it has been used.

- $uri->host
- $uri->host( $new\_host )

    Sets and returns the unescaped hostname.

    If the `$new_host` string ends with a colon and a number, then this
    number also sets the port.

    For IPv6 addresses the brackets around the raw address is removed in the return
    value from $uri->host.  When setting the host attribute to an IPv6 address you
    can use a raw address or one enclosed in brackets.  The address needs to be
    enclosed in brackets if you want to pass in a new port value as well.

        my $uri = URI->new("http://www.\xC3\xBCri-sample/foo/bar.html");
        print $u->host; # www.xn--ri-sample-fra0f

- $uri->ihost

    Returns the host in Unicode form. Any IDNA A-labels (encoded unicode chars with
    _xn--_ prefix) are turned into U-labels (unicode chars).

        my $uri = URI->new("http://www.\xC3\xBCri-sample/foo/bar.html");
        print $u->ihost; # www.\xC3\xBCri-sample

- $uri->port
- $uri->port( $new\_port )

    Sets and returns the port.  The port is a simple integer
    that should be greater than 0.

    If a port is not specified explicitly in the URI, then the URI scheme's default port
    is returned. If you don't want the default port
    substituted, then you can use the $uri->\_port method instead.

- $uri->host\_port
- $uri->host\_port( $new\_host\_port )

    Sets and returns the host and port as a single
    unit.  The returned value includes a port, even if it matches the
    default port.  The host part and the port part are separated by a
    colon: ":".

    For IPv6 addresses the bracketing is preserved; thus
    URI->new("http://\[::1\]/")->host\_port returns "\[::1\]:80".  Contrast this with
    $uri->host which will remove the brackets.

- $uri->default\_port

    Returns the default port of the URI scheme to which $uri
    belongs.  For _http_ this is the number 80, for _ftp_ this
    is the number 21, etc.  The default port for a scheme can not be
    changed.

# SCHEME-SPECIFIC SUPPORT

Scheme-specific support is provided for the following URI schemes.  For `URI`
objects that do not belong to one of these, you can only use the common and
generic methods.

- **data**:

    The _data_ URI scheme is specified in RFC 2397.  It allows inclusion
    of small data items as "immediate" data, as if it had been included
    externally.

    `URI` objects belonging to the data scheme support the common methods
    and two new methods to access their scheme-specific components:
    $uri->media\_type and $uri->data.  See [URI::data](https://metacpan.org/pod/URI%3A%3Adata) for details.

- **file**:

    An old specification of the _file_ URI scheme is found in RFC 1738.
    A new RFC 2396 based specification in not available yet, but file URI
    references are in common use.

    `URI` objects belonging to the file scheme support the common and
    generic methods.  In addition, they provide two methods for mapping file URIs
    back to local file names; $uri->file and $uri->dir.  See [URI::file](https://metacpan.org/pod/URI%3A%3Afile)
    for details.

- **ftp**:

    An old specification of the _ftp_ URI scheme is found in RFC 1738.  A
    new RFC 2396 based specification in not available yet, but ftp URI
    references are in common use.

    `URI` objects belonging to the ftp scheme support the common,
    generic and server methods.  In addition, they provide two methods for
    accessing the userinfo sub-components: $uri->user and $uri->password.

- **gopher**:

    The _gopher_ URI scheme is specified in
    &lt;draft-murali-url-gopher-1996-12-04> and will hopefully be available
    as a RFC 2396 based specification.

    `URI` objects belonging to the gopher scheme support the common,
    generic and server methods. In addition, they support some methods for
    accessing gopher-specific path components: $uri->gopher\_type,
    $uri->selector, $uri->search, $uri->string.

- **http**:

    The _http_ URI scheme is specified in RFC 2616.
    The scheme is used to reference resources hosted by HTTP servers.

    `URI` objects belonging to the http scheme support the common,
    generic and server methods.

- **https**:

    The _https_ URI scheme is a Netscape invention which is commonly
    implemented.  The scheme is used to reference HTTP servers through SSL
    connections.  Its syntax is the same as http, but the default
    port is different.

- **ldap**:

    The _ldap_ URI scheme is specified in RFC 2255.  LDAP is the
    Lightweight Directory Access Protocol.  An ldap URI describes an LDAP
    search operation to perform to retrieve information from an LDAP
    directory.

    `URI` objects belonging to the ldap scheme support the common,
    generic and server methods as well as ldap-specific methods: $uri->dn,
    $uri->attributes, $uri->scope, $uri->filter, $uri->extensions.  See
    [URI::ldap](https://metacpan.org/pod/URI%3A%3Aldap) for details.

- **ldapi**:

    Like the _ldap_ URI scheme, but uses a UNIX domain socket.  The
    server methods are not supported, and the local socket path is
    available as $uri->un\_path.  The _ldapi_ scheme is used by the
    OpenLDAP package.  There is no real specification for it, but it is
    mentioned in various OpenLDAP manual pages.

- **ldaps**:

    Like the _ldap_ URI scheme, but uses an SSL connection.  This
    scheme is deprecated, as the preferred way is to use the _start\_tls_
    mechanism.

- **mailto**:

    The _mailto_ URI scheme is specified in RFC 2368.  The scheme was
    originally used to designate the Internet mailing address of an
    individual or service.  It has (in RFC 2368) been extended to allow
    setting of other mail header fields and the message body.

    `URI` objects belonging to the mailto scheme support the common
    methods and the generic query methods.  In addition, they support the
    following mailto-specific methods: $uri->to, $uri->headers.

    Note that the "foo@example.com" part of a mailto is _not_ the
    `userinfo` and `host` but instead the `path`.  This allows a
    mailto URI to contain multiple comma separated email addresses.

- **mms**:

    The _mms_ URL specification can be found at [http://sdp.ppona.com/](http://sdp.ppona.com/).
    `URI` objects belonging to the mms scheme support the common,
    generic, and server methods, with the exception of userinfo and
    query-related sub-components.

- **news**:

    The _news_, _nntp_ and _snews_ URI schemes are specified in
    &lt;draft-gilman-news-url-01> and will hopefully be available as an RFC
    2396 based specification soon. (Update: as of April 2010, they are in
    [RFC 5538](https://tools.ietf.org/html/rfc5538).

    `URI` objects belonging to the news scheme support the common,
    generic and server methods.  In addition, they provide some methods to
    access the path: $uri->group and $uri->message.

- **nntp**:

    See _news_ scheme.

- **nntps**:

    See _news_ scheme and [RFC 5538](https://tools.ietf.org/html/rfc5538).

- **pop**:

    The _pop_ URI scheme is specified in RFC 2384. The scheme is used to
    reference a POP3 mailbox.

    `URI` objects belonging to the pop scheme support the common, generic
    and server methods.  In addition, they provide two methods to access the
    userinfo components: $uri->user and $uri->auth

- **rlogin**:

    An old specification of the _rlogin_ URI scheme is found in RFC
    1738\. `URI` objects belonging to the rlogin scheme support the
    common, generic and server methods.

- **rtsp**:

    The _rtsp_ URL specification can be found in section 3.2 of RFC 2326.
    `URI` objects belonging to the rtsp scheme support the common,
    generic, and server methods, with the exception of userinfo and
    query-related sub-components.

- **rtspu**:

    The _rtspu_ URI scheme is used to talk to RTSP servers over UDP
    instead of TCP.  The syntax is the same as rtsp.

- **rsync**:

    Information about rsync is available from [http://rsync.samba.org/](http://rsync.samba.org/).
    `URI` objects belonging to the rsync scheme support the common,
    generic and server methods.  In addition, they provide methods to
    access the userinfo sub-components: $uri->user and $uri->password.

- **sip**:

    The _sip_ URI specification is described in sections 19.1 and 25
    of RFC 3261.  `URI` objects belonging to the sip scheme support the
    common, generic, and server methods with the exception of path related
    sub-components.  In addition, they provide two methods to get and set
    _sip_ parameters: $uri->params\_form and $uri->params.

- **sips**:

    See _sip_ scheme.  Its syntax is the same as sip, but the default
    port is different.

- **snews**:

    See _news_ scheme.  Its syntax is the same as news, but the default
    port is different.

- **telnet**:

    An old specification of the _telnet_ URI scheme is found in RFC
    1738\. `URI` objects belonging to the telnet scheme support the
    common, generic and server methods.

- **tn3270**:

    These URIs are used like _telnet_ URIs but for connections to IBM
    mainframes.  `URI` objects belonging to the tn3270 scheme support the
    common, generic and server methods.

- **ssh**:

    Information about ssh is available at [http://www.openssh.com/](http://www.openssh.com/).
    `URI` objects belonging to the ssh scheme support the common,
    generic and server methods. In addition, they provide methods to
    access the userinfo sub-components: $uri->user and $uri->password.

- **sftp**:

    `URI` objects belonging to the sftp scheme support the common,
    generic and server methods. In addition, they provide methods to
    access the userinfo sub-components: $uri->user and $uri->password.

- **urn**:

    The syntax of Uniform Resource Names is specified in RFC 2141.  `URI`
    objects belonging to the urn scheme provide the common methods, and also the
    methods $uri->nid and $uri->nss, which return the Namespace Identifier
    and the Namespace-Specific String respectively.

    The Namespace Identifier basically works like the Scheme identifier of
    URIs, and further divides the URN namespace.  Namespace Identifier
    assignments are maintained at
    [http://www.iana.org/assignments/urn-namespaces](http://www.iana.org/assignments/urn-namespaces).

    Letter case is not significant for the Namespace Identifier.  It is
    always returned in lower case by the $uri->nid method.  The $uri->\_nid
    method can be used if you want it in its original case.

- **urn**:**isbn**:

    The `urn:isbn:` namespace contains International Standard Book
    Numbers (ISBNs) and is described in RFC 3187.  A `URI` object belonging
    to this namespace has the following extra methods (if the
    Business::ISBN module is available): $uri->isbn,
    $uri->isbn\_publisher\_code, $uri->isbn\_group\_code (formerly isbn\_country\_code,
    which is still supported by issues a deprecation warning), $uri->isbn\_as\_ean.

- **urn**:**oid**:

    The `urn:oid:` namespace contains Object Identifiers (OIDs) and is
    described in RFC 3061.  An object identifier consists of sequences of digits
    separated by dots.  A `URI` object belonging to this namespace has an
    additional method called $uri->oid that can be used to get/set the oid
    value.  In a list context, oid numbers are returned as separate elements.

# CONFIGURATION VARIABLES

The following configuration variables influence how the class and its
methods behave:

- $URI::ABS\_ALLOW\_RELATIVE\_SCHEME

    Some older parsers used to allow the scheme name to be present in the
    relative URL if it was the same as the base URL scheme.  RFC 2396 says
    that this should be avoided, but you can enable this old behaviour by
    setting the $URI::ABS\_ALLOW\_RELATIVE\_SCHEME variable to a TRUE value.
    The difference is demonstrated by the following examples:

        URI->new("http:foo")->abs("http://host/a/b")
            ==>  "http:foo"

        local $URI::ABS_ALLOW_RELATIVE_SCHEME = 1;
        URI->new("http:foo")->abs("http://host/a/b")
            ==>  "http:/host/a/foo"

- $URI::ABS\_REMOTE\_LEADING\_DOTS

    You can also have the abs() method ignore excess ".."
    segments in the relative URI by setting $URI::ABS\_REMOTE\_LEADING\_DOTS
    to a TRUE value.  The difference is demonstrated by the following
    examples:

        URI->new("../../../foo")->abs("http://host/a/b")
            ==> "http://host/../../foo"

        local $URI::ABS_REMOTE_LEADING_DOTS = 1;
        URI->new("../../../foo")->abs("http://host/a/b")
            ==> "http://host/foo"

- $URI::DEFAULT\_QUERY\_FORM\_DELIMITER

    This value can be set to ";" to have the query form `key=value` pairs
    delimited by ";" instead of "&" which is the default.

# ENVIRONMENT VARIABLES

- URI\_HAS\_RESERVED\_SQUARE\_BRACKETS

    Before version 5.11, URI treated square brackets as reserved characters
    throughout the whole URI string. However, these brackets are reserved
    only within the authority/host part of the URI and nowhere else (RFC 3986).

    Starting with version 5.11, URI takes this distinction into account.
    Setting the environment variable `URI_HAS_RESERVED_SQUARE_BRACKETS`
    (programmatically or via the shell), restores the old behavior.

        #-- restore 5.10 behavior programmatically
        BEGIN {
          $ENV{URI_HAS_RESERVED_SQUARE_BRACKETS} = 1;
        }
        use URI ();

    _Note_: This environment variable is just used during initialization and has to be set
          _before_ module URI is used/required. Changing it at run time has no effect.

    Its value can be checked programmatically by accessing the constant
    `URI::HAS_RESERVED_SQUARE_BRACKETS`.

# BUGS

There are some things that are not quite right:

- Using regexp variables like $1 directly as arguments to the URI accessor methods
does not work too well with current perl implementations.  I would argue
that this is actually a bug in perl.  The workaround is to quote
them. Example:

        /(...)/ || die;
        $u->query("$1");

- The escaping (percent encoding) of chars in the 128 .. 255 range passed to the
URI constructor or when setting URI parts using the accessor methods depend on
the state of the internal UTF8 flag (see utf8::is\_utf8) of the string passed.
If the UTF8 flag is set the UTF-8 encoded version of the character is percent
encoded.  If the UTF8 flag isn't set the Latin-1 version (byte) of the
character is percent encoded.  This basically exposes the internal encoding of
Perl strings.

# PARSING URIs WITH REGEXP

As an alternative to this module, the following (official) regular
expression can be used to decode a URI:

    my($scheme, $authority, $path, $query, $fragment) =
    $uri =~ m|(?:([^:/?#]+):)?(?://([^/?#]*))?([^?#]*)(?:\?([^#]*))?(?:#(.*))?|;

The `URI::Split` module provides the function uri\_split() as a
readable alternative.

# SEE ALSO

[URI::file](https://metacpan.org/pod/URI%3A%3Afile), [URI::WithBase](https://metacpan.org/pod/URI%3A%3AWithBase), [URI::Escape](https://metacpan.org/pod/URI%3A%3AEscape),
[URI::Split](https://metacpan.org/pod/URI%3A%3ASplit), [URI::Heuristic](https://metacpan.org/pod/URI%3A%3AHeuristic)

RFC 2396: "Uniform Resource Identifiers (URI): Generic Syntax",
Berners-Lee, Fielding, Masinter, August 1998.

[http://www.iana.org/assignments/uri-schemes](http://www.iana.org/assignments/uri-schemes)

[http://www.iana.org/assignments/urn-namespaces](http://www.iana.org/assignments/urn-namespaces)

[http://www.w3.org/Addressing/](http://www.w3.org/Addressing/)

# COPYRIGHT

Copyright 1995-2009 Gisle Aas.

Copyright 1995 Martijn Koster.

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

# AUTHORS / ACKNOWLEDGMENTS

This module is based on the `URI::URL` module, which in turn was
(distantly) based on the `wwwurl.pl` code in the libwww-perl for
perl4 developed by Roy Fielding, as part of the Arcadia project at the
University of California, Irvine, with contributions from Brooks
Cutter.

`URI::URL` was developed by Gisle Aas, Tim Bunce, Roy Fielding and
Martijn Koster with input from other people on the libwww-perl mailing
list.

`URI` and related subclasses was developed by Gisle Aas.