Note: Beginning users who want a non-technical introduction to explaining things should see "expl expl intro".
explain [option]* [topic or sub-topic]*
(+|-)Paginate (-) (+|-)Verbose Pagelength=number (+|-)indeX (+) Starts=string
expl expl fortran hints expl b lib printf pl=10 expl ec >temp -- directs the explain to a file
Starts="Description:"
starts displaying the explain information beginning with the "Description:" line.
EXPLAIN provides on-line information about TSS commands, subsystems, language processors, and other features. Explanations are stored in files under the userid EXPL or LIBRARY/EXPL. The EXPL command automatically searches both locations to find a desired explain file.
When you enter an EXPL command, the EXPLAIN subsystem forms a pathname from the command line by replacing strings of one or more blanks with a slash. For example,
expl fortran batch
is changed into the pathname
expl/fortran/batch
EXPL then examines each piece of the pathname from left to right, verifying that the pathname component exists. In the above example, EXPL would check for the existence of
expl expl/fortran expl/fortran/batch
If a component of a pathname does not exist as it stands, it is truncated, first to six characters, and then to four characters if the first truncation fails. In the above example, suppose EXPL finds there is no file or directory named "expl/fortran". EXPL then tries "expl/fortra". If that also fails, EXPL looks for "expl/fort". If "expl/fort" exists, EXPL then uses this new pathname in future searches. For example, it searches for
expl/fort/batch
If that doesn't exist, EXPL truncates the final pathname component to
expl/fort/batc
If this file exists, EXPL uses takes this as the desired explain file.
If a topic has several sub-topics, its main explain file is stored in the file "expl" underneath the topic catalog. For example, the explain file corresponding to "expl fortran" is
expl/fort/expl
because "expl/fort" is a catalog.
When EXPL finds an explain file corresponding to the topic on the command line, EXPL checks to see if the file is sequential or random. If the file is sequential, EXPL simply displays the contents of the file as text. If the file is random, EXPL executes the file as a program. In this way, your site may create explain files which run as programs and obtain information from a variety of sources.
Sometimes EXPL cannot find a file that matches your topic. This can happen because you make a typing error when entering the topic or because an explain file hasn't been created for the topic. In this case, EXPL displays "unable to explain" and asks if you want an index. If you answer "yes" or "y", EXPL displays the closest index to the topic you tried to explain. For example, suppose you enter
expl trace trace zxcvbnm
EXPL first tries to display
expl trace trace index
If this index doesn't exist, EXPL tries
expl trace index
then
expl index
If you don't want EXPL to look for an index in this way, specify the -indeX option on the command line.
By default, EXPL does not paginate its output. If a pagination option is specified on the command line, EXPL paginates according to the following conventions.
Even EXPL does not paginate your output, the output may still be paginated by TSS if you have used STTY to ask for pagination; see "expl stty" for more information.
Copyright © 1996, Thinkage Ltd.