cpython/Doc/lib/libcmd.tex

\section{\module{cmd} ---
         Support for line-oriented command interpreters}

\declaremodule{standard}{cmd}
\sectionauthor{Eric S. Raymond}{esr@snark.thyrsus.com}
\modulesynopsis{Build line-oriented command interpreters.}


The \class{Cmd} class provides a simple framework for writing
line-oriented command interpreters.  These are often useful for
test harnesses, administrative tools, and prototypes that will
later be wrapped in a more sophisticated interface.

\begin{classdesc}{Cmd}{\optional{completekey}}
A \class{Cmd} instance or subclass instance is a line-oriented
interpreter framework.  There is no good reason to instantiate
\class{Cmd} itself; rather, it's useful as a superclass of an
interpreter class you define yourself in order to inherit
\class{Cmd}'s methods and encapsulate action methods.

The optional argument is the \refmodule{readline} name of a completion
key; it defaults to \code{``tab''}. If \var{completekey} is not
\code{None} and \module{readline} is available, command completion is
done automatically.

\end{classdesc}

\subsection{Cmd Objects}
\label{Cmd-objects}

A \class{Cmd} instance has the following methods:

\begin{methoddesc}{cmdloop}{\optional{intro}}
Repeatedly issue a prompt, accept input, parse an initial prefix off
the received input, and dispatch to action methods, passing them the
remainder of the line as argument.

The optional argument is a banner or intro string to be issued before the
first prompt (this overrides the \member{intro} class member).

If the \module{readline} module is loaded, input will automatically
inherit \program{bash}-like history-list editing (e.g. \kbd{Control-P}
scrolls back to the last command, \kbd{Control-N} forward to the next
one, \kbd{Control-F} moves the cursor to the right non-destructively,
\kbd{Control-B} moves the cursor to the left non-destructively, etc.).

An end-of-file on input is passed back as the string \code{'EOF'}.

An interpreter instance will recognize a command name \samp{foo} if
and only if it has a method \method{do_foo()}.  As a special case,
a line beginning with the character \character{?} is dispatched to
the method \method{do_help()}.  As another special case, a line
beginning with the character \character{!} is dispatched to the
method \method{do_shell} (if such a method is defined).

If completion is enabled, completing commands will be done
automatically, and completing of commands args is done by calling
\method{complete_foo()} with arguments \samp{text}, \samp{line},
\samp{begidx}, \samp{endidx}.  \samp{text} is string we are matching
against, all returned matches must begin with it.  \samp{line} is the
current input line (lstripped), \samp{begidx} and \samp{endidx} are
the beginning and end indexes of the text being matched, which could
be used to provide different completion depending upon which position
the argument is in.

All subclasses of \class{Cmd} inherit a predefined \method{do_help}.
This method, called with an argument \code{bar}, invokes the
corresponding method \method{help_bar()}.  With no argument,
\method{do_help()} lists all available help topics (that is, all
commands with corresponding \method{help_*()} methods), and also lists
any undocumented commands.
\end{methoddesc}

\begin{methoddesc}{onecmd}{str}
Interpret the argument as though it had been typed in in
response to the prompt.
\end{methoddesc}

\begin{methoddesc}{emptyline}{}
Method called when an empty line is entered in response to the prompt.
If this method is not overridden, it repeats the last nonempty command
entered.  
\end{methoddesc}

\begin{methoddesc}{default}{line}
Method called on an input line when the command prefix is not
recognized. If this method is not overridden, it prints an
error message and returns.
\end{methoddesc}

\begin{methoddesc}{completedefault}{text, line, begidx, endidx}
Method called to complete an input line when no command-specific
\code{complete_} method is available. By default, it returns an
empty list.
\end{methoddesc}

\begin{methoddesc}{precmd}{}
Hook method executed just before the command line is interpreted, but
after the input prompt is generated and issued.  This
method is a stub in \class{Cmd}; it exists to be overridden by
subclasses.
\end{methoddesc}

\begin{methoddesc}{postcmd}{}
Hook method executed just after a command dispatch is finished.  This
method is a stub in \class{Cmd}; it exists to be overridden by
subclasses.
\end{methoddesc}

\begin{methoddesc}{preloop}{}
Hook method executed once when \method{cmdloop()} is called.  This
method is a stub in \class{Cmd}; it exists to be overridden by
subclasses.
\end{methoddesc}

\begin{methoddesc}{postloop}{}
Hook method executed once when \method{cmdloop()} is about to return.
This method is a stub in \class{Cmd}; it exists to be overridden by
subclasses.
\end{methoddesc}

Instances of \class{Cmd} subclasses have some public instance variables:

\begin{memberdesc}{prompt}
The prompt issued to solicit input.
\end{memberdesc}

\begin{memberdesc}{identchars}
The string of characters accepted for the command prefix.
\end{memberdesc}

\begin{memberdesc}{lastcmd}
The last nonempty command prefix seen. 
\end{memberdesc}

\begin{memberdesc}{intro}
A string to issue as an intro or banner.  May be overridden by giving
the \method{cmdloop()} method an argument.
\end{memberdesc}

\begin{memberdesc}{doc_header}
The header to issue if the help output has a section for documented
commands.
\end{memberdesc}

\begin{memberdesc}{misc_header}
The header to issue if the help output has a section for miscellaneous 
help topics (that is, there are \method{help_*()} methods without
corresponding \method{do_*()} methods).
\end{memberdesc}

\begin{memberdesc}{undoc_header}
The header to issue if the help output has a section for undocumented 
commands (that is, there are \method{do_*()} methods without
corresponding \method{help_*()} methods).
\end{memberdesc}

\begin{memberdesc}{ruler}
The character used to draw separator lines under the help-message
headers.  If empty, no ruler line is drawn.  It defaults to
\character{=}.
\end{memberdesc}

\begin{memberdesc}{use_rawinput}
A flag, defaulting to true.  If true, \method{cmdloop()} uses
\function{raw_input()} to display a prompt and read the next command;
if false, \function{sys.stdout.write()} and
\function{sys.stdin.readline()} are used. (This means that by
importing \module{readline}, on systems that support it, the
interpreter will automatically support Emacs-like line editing 
and command-history keystrokes.)
\end{memberdesc}