142 lines
4.9 KiB
TeX
142 lines
4.9 KiB
TeX
\section{\module{cmd} ---
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Support for line-oriented command interpreters}
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\declaremodule{standard}{cmd}
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\sectionauthor{Eric S. Raymond}{esr@snark.thyrsus.com}
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\modulesynopsis{Build line-oriented command interpreters.}
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The \class{Cmd} class provides a simple framework for writing
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line-oriented command interpreters. These are often useful for
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test harnesses, administrative tools, and prototypes that will
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later be wrapped in a more sophisticated interface.
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\begin{classdesc}{Cmd}{}
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A \class{Cmd} instance or subclass instance is a line-oriented
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interpreter framework. There is no good reason to instantiate
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\class{Cmd} itself; rather, it's useful as a superclass of an
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interpreter class you define yourself in order to inherit
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\class{Cmd}'s methods and encapsulate action methods.
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\end{classdesc}
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\subsection{Cmd Objects}
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\label{Cmd-objects}
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A \class{Cmd} instance has the following methods:
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\begin{methoddesc}{cmdloop}{\optional{intro}}
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Repeatedly issue a prompt, accept input, parse an initial prefix off
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the received input, and dispatch to action methods, passing them the
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remainder of the line as argument.
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The optional argument is a banner or intro string to be issued before the
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first prompt (this overrides the \member{intro} class member).
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If the \module{readline} module is loaded, input will automatically
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inherit \program{bash}-like history-list editing (e.g. \kbd{Ctrl-P}
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scrolls back to the last command, \kbd{Ctrl-N} forward to the next
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one, \kbd{Ctrl-F} moves the cursor to the right non-destructively,
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\kbd{Ctrl-B} moves the cursor to the left non-destructively, etc.).
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An end-of-file on input is passed back as the string \code{'EOF'}.
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An interpreter instance will recognize a command name \samp{foo} if
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and only if it has a method \method{do_foo()}. As a special case,
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a line beginning with the character \character{?} is dispatched to
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the method \method{do_help()}. As another special case, a line
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beginning with the character \character{!} is dispatched to the
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method \method{do_shell} (if such a method is defined).
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All subclasses of \class{Cmd} inherit a predefined \method{do_help}.
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This method, called with an argument \code{bar}, invokes the
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corresponding method \method{help_bar()}. With no argument,
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\method{do_help()} lists all available help topics (that is, all
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commands with corresponding \method{help_*()} methods), and also lists
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any undocumented commands.
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\end{methoddesc}
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\begin{methoddesc}{onecmd}{str}
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Interpret the argument as though it had been typed in in
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response to the prompt.
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\end{methoddesc}
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\begin{methoddesc}{emptyline}{}
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Method called when an empty line is entered in response to the prompt.
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If this method is not overridden, it repeats the last nonempty command
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entered.
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\end{methoddesc}
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\begin{methoddesc}{default}{line}
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Method called on an input line when the command prefix is not
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recognized. If this method is not overridden, it prints an
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error message and returns.
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\end{methoddesc}
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\begin{methoddesc}{precmd}{}
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Hook method executed just before the input prompt is issued. This
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method is a stub in \class{Cmd}; it exists to be overridden by
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subclasses.
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\end{methoddesc}
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\begin{methoddesc}{postcmd}{}
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Hook method executed just after a command dispatch is finished. This
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method is a stub in \class{Cmd}; it exists to be overridden by
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subclasses.
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\end{methoddesc}
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\begin{methoddesc}{preloop}{}
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Hook method executed once when \method{cmdloop()} is called. This
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method is a stub in \class{Cmd}; it exists to be overridden by
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subclasses.
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\end{methoddesc}
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\begin{methoddesc}{postloop}{}
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Hook method executed once when \method{cmdloop()} is about to return.
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This method is a stub in \class{Cmd}; it exists to be overridden by
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subclasses.
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\end{methoddesc}
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Instances of \class{Cmd} subclasses have some public instance variables:
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\begin{memberdesc}{prompt}
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The prompt issued to solicit input.
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\end{memberdesc}
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\begin{memberdesc}{identchars}
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The string of characters accepted for the command prefix.
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\end{memberdesc}
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\begin{memberdesc}{lastcmd}
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The last nonempty command prefix seen.
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\end{memberdesc}
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\begin{memberdesc}{intro}
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A string to issue as an intro or banner. May be overridden by giving
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the \method{cmdloop()} method an argument.
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\end{memberdesc}
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\begin{memberdesc}{doc_header}
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The header to issue if the help output has a section for documented
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commands.
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\end{memberdesc}
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\begin{memberdesc}{misc_header}
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The header to issue if the help output has a section for miscellaneous
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help topics (that is, there are \method{help_*()} methods without
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corresponding \method{do_*()} methods).
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\end{memberdesc}
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\begin{memberdesc}{undoc_header}
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The header to issue if the help output has a section for undocumented
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commands (that is, there are \method{do_*()} methods without
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corresponding \method{help_*()} methods).
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\end{memberdesc}
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\begin{memberdesc}{ruler}
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The character used to draw separator lines under the help-message
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headers. If empty, no ruler line is drawn. It defaults to
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\character{=}.
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\end{memberdesc}
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