< Object

CGI class. See documentation for the file cgi.rb for an overview of the CGI protocol.


CGI is a large class, providing several categories of methods, many of which are mixed in from other modules. Some of the documentation is in this class, some in the modules CGI::QueryExtension and CGI::HtmlExtension. See CGI::Cookie for specific information on handling cookies, and cgi/session.rb (CGI::Session) for information on sessions.

For queries, CGI provides methods to get at environmental variables, parameters, cookies, and multipart request data. For responses, CGI provides methods for writing output and generating HTML.

Read on for more details. Examples are provided at the bottom.


The CGI class dynamically mixes in parameter and cookie-parsing functionality, environmental variable access, and support for parsing multipart requests (including uploaded files) from the CGI::QueryExtension module.

Environmental Variables

The standard CGI environmental variables are available as read-only attributes of a CGI object. The following is a list of these variables:

  AUTH_TYPE               HTTP_HOST          REMOTE_IDENT
  HTTP_FROM               REMOTE_HOST

For each of these variables, there is a corresponding attribute with the same name, except all lower case and without a preceding HTTP_. content_length and server_port are integers; the rest are strings.


The method params() returns a hash of all parameters in the request as name/value-list pairs, where the value-list is an Array of one or more values. The CGI object itself also behaves as a hash of parameter names to values, but only returns a single value (as a String) for each parameter name.

For instance, suppose the request contains the parameter "favourite_colours" with the multiple values "blue" and "green". The following behaviour would occur:

  cgi.params["favourite_colours"]  # => ["blue", "green"]
  cgi["favourite_colours"]         # => "blue"

If a parameter does not exist, the former method will return an empty array, the latter an empty string. The simplest way to test for existence of a parameter is by the has_key? method.


HTTP Cookies are automatically parsed from the request. They are available from the cookies() accessor, which returns a hash from cookie name to CGI::Cookie object.

Multipart requests

If a request‘s method is POST and its content type is multipart/form-data, then it may contain uploaded files. These are stored by the QueryExtension module in the parameters of the request. The parameter name is the name attribute of the file input field, as usual. However, the value is not a string, but an IO object, either an IOString for small files, or a Tempfile for larger ones. This object also has the additional singleton methods:

local_path():the path of the uploaded file on the local filesystem
original_filename():the name of the file on the client computer
content_type():the content type of the file


The CGI class provides methods for sending header and content output to the HTTP client, and mixes in methods for programmatic HTML generation from CGI::HtmlExtension and CGI::TagMaker modules. The precise version of HTML to use for HTML generation is specified at object creation time.

Writing output

The simplest way to send output to the HTTP client is using the out() method. This takes the HTTP headers as a hash parameter, and the body content via a block. The headers can be generated as a string using the header() method. The output stream can be written directly to using the print() method.

Generating HTML

Each HTML element has a corresponding method for generating that element as a String. The name of this method is the same as that of the element, all lowercase. The attributes of the element are passed in as a hash, and the body as a no-argument block that evaluates to a String. The HTML generation module knows which elements are always empty, and silently drops any passed-in body. It also knows which elements require matching closing tags and which don‘t. However, it does not know what attributes are legal for which elements.

There are also some additional HTML generation methods mixed in from the CGI::HtmlExtension module. These include individual methods for the different types of form inputs, and methods for elements that commonly take particular attributes where the attributes can be directly specified as arguments, rather than via a hash.

Examples of use

Get form values

  require "cgi"
  cgi =
  value = cgi['field_name']   # <== value string for 'field_name'
    # if not 'field_name' included, then return "".
  fields = cgi.keys            # <== array of field names

  # returns true if form has 'field_name'

CAUTION! cgi[‘field_name’] returned an Array with the old cgi.rb(included in ruby 1.6)

Get form values as hash

  require "cgi"
  cgi =
  params = cgi.params

cgi.params is a hash.

  cgi.params['new_field_name'] = ["value"]  # add new param
  cgi.params['field_name'] = ["new_value"]  # change value
  cgi.params.delete('field_name')           # delete param
  cgi.params.clear                          # delete all params

Save form values to file

  require "pstore"
  db ="query.db")
  db.transaction do
    db["params"] = cgi.params

Restore form values from file

  require "pstore"
  db ="query.db")
  db.transaction do
    cgi.params = db["params"]

Get multipart form values

  require "cgi"
  cgi =
  value = cgi['field_name']   # <== value string for 'field_name'                  # <== body of value
  value.local_path            # <== path to local file of value
  value.original_filename     # <== original filename of value
  value.content_type          # <== content_type of value

and value has StringIO or Tempfile class methods.

Get cookie values

  require "cgi"
  cgi =
  values = cgi.cookies['name']  # <== array of 'name'
    # if not 'name' included, then return [].
  names = cgi.cookies.keys      # <== array of cookie names

and cgi.cookies is a hash.

Get cookie objects

  require "cgi"
  cgi =
  for name, cookie in cgi.cookies
    cookie.expires = + 30
  cgi.out("cookie" => cgi.cookies) {"string"}

  cgi.cookies # { "name1" => cookie1, "name2" => cookie2, ... }

  require "cgi"
  cgi =
  cgi.cookies['name'].expires = + 30
  cgi.out("cookie" => cgi.cookies['name']) {"string"}

Print http header and html string to $DEFAULT_OUTPUT ($>)

  require "cgi"
  cgi ="html3")  # add HTML generation methods
  cgi.out() do
    cgi.html() do
      cgi.head{ cgi.title{"TITLE"} } +
      cgi.body() do
        cgi.form() do
          cgi.textarea("get_text") +
        end +
        cgi.pre() do
            "params: " + cgi.params.inspect + "\n" +
            "cookies: " + cgi.cookies.inspect + "\n" +
            ENV.collect() do |key, value|
              key + " --> " + value + "\n"

  # add HTML generation methods"html3")    # html3.2"html4")    # html4.01 (Strict)"html4Tr")  # html4.01 Transitional"html4Fr")  # html4.01 Frameset

Classes & Modules


Name   Description
CR = "\015"
LF = "\012"
RFC822_DAYS = %w[ Sun Mon Tue Wed Thu Fri Sat ]
RFC822_MONTHS = %w[ Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec ]


Name Visibility R/W Description
cookie public R
inputs public R



Visibility Signature
public cookie (options)
public error ()
public escape (str)
public escape (string)
public escapeElement (string, *elements)
public escapeHTML (str)
public escapeHTML (string)
public header (*options)
public message (message, title = "", header = ["Content-Type: text/html"])
public new (input = $stdin)
public new (type = "query")
public parse (query)
public pretty (string, shift = " ")
public print (*options) {|.to_s| ...}
public rfc1123_date (time)
public rfc1123_date (time)
public tag (element, attributes = {}) {|.to_s + "</" + escapeHTML(element) + ">" : "")| ...}
public unescape (string)
public unescape (str)
public unescapeElement (string, *elements)
public unescapeHTML (string)


Visibility Signature
public header (options = "text/html")
public out (options = "text/html") {|| ...}
public print (*options)
public read_from_cmdline ()

Class Method Detail


make raw cookie string


print error message to $> and exit


escape url encode


URL-encode a string.

  url_encoded_string = CGI::escape("'Stop!' said Fred")
     # => "%27Stop%21%27+said+Fred"

escapeElement(string, *elements)

Escape only the tags of certain HTML elements in string.

Takes an element or elements or array of elements. Each element is specified by the name of the element, without angle brackets. This matches both the start and the end tag of that element. The attribute list of the open tag will also be escaped (for instance, the double-quotes surrounding attribute values).

  print CGI::escapeElement('<BR><A HREF="url"></A>', "A", "IMG")
    # "<BR>&lt;A HREF=&quot;url&quot;&gt;&lt;/A&gt"

  print CGI::escapeElement('<BR><A HREF="url"></A>', ["A", "IMG"])
    # "<BR>&lt;A HREF=&quot;url&quot;&gt;&lt;/A&gt"


escape HTML


Escape special characters in HTML, namely &\"<>

  CGI::escapeHTML('Usage: foo "bar" <baz>')
     # => "Usage: foo &quot;bar&quot; &lt;baz&gt;"


make HTTP header string

message(message, title = "", header = ["Content-Type: text/html"])

print message to $>

new(input = $stdin)

new(type = "query")

Creates a new CGI instance.

type specifies which version of HTML to load the HTML generation methods for. The following versions of HTML are supported:

html3:HTML 3.x
html4:HTML 4.0
html4Tr:HTML 4.0 Transitional
html4Fr:HTML 4.0 with Framesets

If not specified, no HTML generation methods will be loaded.

If the CGI object is not created in a standard CGI call environment (that is, it can‘t locate REQUEST_METHOD in its environment), then it will run in "offline" mode. In this mode, it reads its parameters from the command line or (failing that) from standard input. Otherwise, cookies and other parameters are parsed automatically from the standard CGI locations, which varies according to the REQUEST_METHOD.


Parse an HTTP query string into a hash of key=>value pairs.

  params = CGI::parse("query_string")
    # {"name1" => ["value1", "value2", ...],
    #  "name2" => ["value1", "value2", ...], ... }

pretty(string, shift = " ")

Prettify (indent) an HTML string.

string is the HTML string to indent. shift is the indentation unit to use; it defaults to two spaces.

  print CGI::pretty("<HTML><BODY></BODY></HTML>")
    # <HTML>
    #   <BODY>
    #   </BODY>
    # </HTML>

  print CGI::pretty("<HTML><BODY></BODY></HTML>", "\t")
    # <HTML>
    #         <BODY>
    #         </BODY>
    # </HTML>

print(*options) {|.to_s| ...}

print HTTP header and string to $>


Format a Time object as a String using the format specified by RFC 1123.

    # Sat, 01 Jan 2000 00:00:00 GMT


make rfc1123 date string

tag(element, attributes = {}) {|.to_s + "</" + escapeHTML(element) + ">" : "")| ...}

make HTML tag string


URL-decode a string.

  string = CGI::unescape("%27Stop%21%27+said+Fred")
     # => "'Stop!' said Fred"


unescape url encoded

unescapeElement(string, *elements)

Undo escaping such as that done by CGI::escapeElement()

  print CGI::unescapeElement(
          CGI::escapeHTML('<BR><A HREF="url"></A>'), "A", "IMG")
    # "&lt;BR&gt;<A HREF="url"></A>"

  print CGI::unescapeElement(
          CGI::escapeHTML('<BR><A HREF="url"></A>'), ["A", "IMG"])
    # "&lt;BR&gt;<A HREF="url"></A>"


Unescape a string that has been HTML-escaped

  CGI::unescapeHTML("Usage: foo &quot;bar&quot; &lt;baz&gt;")
     # => "Usage: foo \"bar\" <baz>"

Instance Method Detail

header(options = "text/html")

Create an HTTP header block as a string.

Includes the empty line that ends the header block.

options can be a string specifying the Content-Type (defaults to text/html), or a hash of header key/value pairs. The following header keys are recognized:

type:the Content-Type header. Defaults to "text/html"
charset:the charset of the body, appended to the Content-Type header.
nph:a boolean value. If true, prepend protocol string and status code, and date; and sets default values for "server" and "connection" if not explicitly set.
status:the HTTP status code, returned as the Status header. See the list of available status codes below.
server:the server software, returned as the Server header.
connection:the connection type, returned as the Connection header (for instance, "close".
length:the length of the content that will be sent, returned as the Content-Length header.
language:the language of the content, returned as the Content-Language header.
expires:the time on which the current content expires, as a Time object, returned as the Expires header.
cookie:a cookie or cookies, returned as one or more Set-Cookie headers. The value can be the literal string of the cookie; a CGI::Cookie object; an Array of literal cookie strings or Cookie objects; or a hash all of whose values are literal cookie strings or Cookie objects. These cookies are in addition to the cookies held in the @output_cookies field.

Other header lines can also be set; they are appended as key: value.

    # Content-Type: text/html

    # Content-Type: text/plain

  header("nph"        => true,
         "status"     => "OK",  # == "200 OK"
           # "status"     => "200 GOOD",
         "server"     => ENV['SERVER_SOFTWARE'],
         "connection" => "close",
         "type"       => "text/html",
         "charset"    => "iso-2022-jp",
           # Content-Type: text/html; charset=iso-2022-jp
         "length"     => 103,
         "language"   => "ja",
         "expires"    => + 30,
         "cookie"     => [cookie1, cookie2],
         "my_header1" => "my_value"
         "my_header2" => "my_value")

The status codes are:

  "OK"                  --> "200 OK"
  "PARTIAL_CONTENT"     --> "206 Partial Content"
  "MULTIPLE_CHOICES"    --> "300 Multiple Choices"
  "MOVED"               --> "301 Moved Permanently"
  "REDIRECT"            --> "302 Found"
  "NOT_MODIFIED"        --> "304 Not Modified"
  "BAD_REQUEST"         --> "400 Bad Request"
  "AUTH_REQUIRED"       --> "401 Authorization Required"
  "FORBIDDEN"           --> "403 Forbidden"
  "NOT_FOUND"           --> "404 Not Found"
  "METHOD_NOT_ALLOWED"  --> "405 Method Not Allowed"
  "NOT_ACCEPTABLE"      --> "406 Not Acceptable"
  "LENGTH_REQUIRED"     --> "411 Length Required"
  "PRECONDITION_FAILED" --> "412 Precondition Failed"
  "SERVER_ERROR"        --> "500 Internal Server Error"
  "NOT_IMPLEMENTED"     --> "501 Method Not Implemented"
  "BAD_GATEWAY"         --> "502 Bad Gateway"
  "VARIANT_ALSO_VARIES" --> "506 Variant Also Negotiates"

This method does not perform charset conversion.

out(options = "text/html") {|| ...}

Print an HTTP header and body to $DEFAULT_OUTPUT ($>)

The header is provided by options, as for header(). The body of the document is that returned by the passed- in block. This block takes no arguments. It is required.

  cgi =
  cgi.out{ "string" }
    # Content-Type: text/html
    # Content-Length: 6
    # string

  cgi.out("text/plain") { "string" }
    # Content-Type: text/plain
    # Content-Length: 6
    # string

  cgi.out("nph"        => true,
          "status"     => "OK",  # == "200 OK"
          "server"     => ENV['SERVER_SOFTWARE'],
          "connection" => "close",
          "type"       => "text/html",
          "charset"    => "iso-2022-jp",
            # Content-Type: text/html; charset=iso-2022-jp
          "language"   => "ja",
          "expires"    => + (3600 * 24 * 30),
          "cookie"     => [cookie1, cookie2],
          "my_header1" => "my_value",
          "my_header2" => "my_value") { "string" }

Content-Length is automatically calculated from the size of the String returned by the content block.

If ENV[‘REQUEST_METHOD’] == "HEAD", then only the header is outputted (the content block is still required, but it is ignored).

If the charset is "iso-2022-jp" or "euc-jp" or "shift_jis" then the content is converted to this charset, and the language is set to "ja".


Print an argument or list of arguments to the default output stream

  cgi =
  cgi.print    # default:  cgi.print == $DEFAULT_OUTPUT.print


offline mode. read name=value pairs on standard input.