3.1.3 The online help system

The online help system is invoked with the help command. ? may be used as a synonym for help. Simply typing help; displays the “top” of the help system (i.e., the title page of the SINGULAR manual) which offers a short table of contents. Typing help topic; shows the available documentation on topic. Here, topic may be either a function name or, more generally, any index entry of the SINGULAR manual. Furthermore, topic may contain wildcard characters. See help, for more information.

Online help information can be displayed in various help browsers. The following table lists a summary of the supported browsers. See below for more details about particular browsers.

The browser which is used to display the help information, can be either set at startup time with the command line option (see Command line options)

--brower=<browser>

or with the SINGULAR command (see system)

system("--browser", <browser>);

The SINGULAR command

system("browsers");

lists all available browsers and the command

system("--browser");

returns the currently used browser.

If no browser is explicitly set by the user, then the first (w.r.t. the order of the browsers in the table above) available browser is chosen. In other words, the default browser is netscape for Unix platforms, and html for Windows, unless your local set-up does not allow to run it.

The .singularrc (see Startup sequence) file is a good place to set your default browser. Recall that if a file $HOME/.singularrc exists on your system, then the content of this file is executed before the first user input. Hence, putting

if (system("version") >= 1306) // keep backwards-compatibility
{
  if (! system("--emacs")
  {
    // only set help browser if not running within emacs
    system("--browser", "info");
  }
  // if help browser is later on set to netscape,
  // allow it to fetch HTML pages from the net
  system("--allow-net", 1);
}; // the last semicolon is important: otherwise no ">", but "." prompt

in your file $HOME/.singularrc sets your default browser to info, unless SINGULAR is run within emacs (in which case the default browser is set automatically to emacs).

Obviously, certain external files and programs are required for the SINGULAR help system to work correctly. If something is not available or goes wrong, here are some tips for troubleshooting the help system:

• Under Unix, the environment variable DISPLAY has to be set for the browsers netscape, tkinfo, and xinfo to work.
• The help browsers netscape, tkinfo, xinfo, and info are only available if the respective programs are installed on your system (for xinfo, the programs xterm and info are necessary). You can explicitly specify which program to use, by setting appropriate environment variables (whose names are the names of the respective programs in all up-case letters).
  For example, to use the program navigator with a private colormap as netscape help browser, set the environment variable NETSCAPE to the value "navigator -install".
• If the help browser netscape can not find the local html pages of the SINGULAR manual (which it looks for at $RootDir/html – see Loading of a library for more info on $RootDir) and the (command-line) option --allow-net has explicitly been set (see Command line options and system for more info on setting values of command-line options), then it dispatches the html pages from http://www.singular.uni-kl.de/Manual (note that the non-local net-access of HTML pages is disabled, by default).
  An alternative location of a local directory where the html pages reside can be specified by setting the environment variable SINGULAR_HTML_DIR.
• The help browsers tkinfo, xinfo, info, and builtin need the (info) file singular.hlp which it looks for at $RootDir/info/singular.hlp (see Loading of a library for more info on $RootDir). An alternative location of the info file of the manual can be specified by setting the environment variable SINGULAR_INFO_FILE.

See also: Command line options; Loading of a library; Startup sequence; system.

Info help browsers

The help browsers tkinfo, xinfo and info (so-called info help browsers) are based on the info program from the Gnu texinfo package. See An Introduction to Info: (info)Top section ‘Getting started’ in The Info Manual, for more information.

For info help browsers, the online manual is decomposed into “nodes” of information, closely related to the division of the printed manual into sections and subsections. A node contains text describing a specific topic at a specific level of detail. The top line of a node is its “header”. The node’s header tells the name of the current node (Node:), the name of the next node (Next:), the name of the previous node (Prev:), and the name of the upper node (Up:).

To move within info, type commands consisting of single characters. Do not type RETURN. Do not use cursor keys, either. Using some of the cursor keys by accident might pop to some totally different node. Type l to return to the original node. Some of the info commands read input from the command line at the bottom line. The TAB key may be used to complete partially entered input.

The most important commands are:

q

leaves the online help system

n

goes to the next node

p

goes to the previous node

u

goes to the upper node

m

picks a menu item specified by name

f

follows a cross reference

l

goes to the previously visited node

b

goes to the beginning of the current node

e

goes to the end of the current node

SPACE

scrolls forward a page

DEL

scrolls backward a page

h

invokes info tutorial (use l to return to the manual or CTRL-X 0 to remove extra window)

CTRL-H

shows a short overview on the online help system (use l to return to the manual or CTRL-X 0 to remove extra window)

s

searches through the manual for a specified string, and selects the node in which the next occurrence is found

1, …, 9

picks i-th subtopic from a menu