Doc/lib/libcmd.tex

   1 \section{\module{cmd} ---
   2          Support for line-oriented command interpreters}
   3
   4 \declaremodule{standard}{cmd}
   5 \sectionauthor{Eric S. Raymond}{esr@snark.thyrsus.com}
   6 \modulesynopsis{Build line-oriented command interpreters.}
   7
   8
   9 The \class{Cmd} class provides a simple framework for writing
  10 line-oriented command interpreters.  These are often useful for
  11 test harnesses, administrative tools, and prototypes that will
  12 later be wrapped in a more sophisticated interface.
  13
  14 \begin{classdesc}{Cmd}{}
  15 A \class{Cmd} instance or subclass instance is a line-oriented
  16 interpreter framework.  There is no good reason to instantiate
  17 \class{Cmd} itself; rather, it's useful as a superclass of an
  18 interpreter class you define yourself in order to inherit
  19 \class{Cmd}'s methods and encapsulate action methods.
  20 \end{classdesc}
  21
  22 \subsection{Cmd Objects}
  23 \label{Cmd-objects}
  24
  25 A \class{Cmd} instance has the following methods:
  26
  27 \begin{methoddesc}{cmdloop}{\optional{intro}}
  28 Repeatedly issue a prompt, accept input, parse an initial prefix off
  29 the received input, and dispatch to action methods, passing them the
  30 remainder of the line as argument.
  31
  32 The optional argument is a banner or intro string to be issued before the
  33 first prompt (this overrides the \member{intro} class member).
  34
  35 If the \module{readline} module is loaded, input will automatically
  36 inherit \program{bash}-like history-list editing (e.g. \kbd{Control-P}
  37 scrolls back to the last command, \kbd{Control-N} forward to the next
  38 one, \kbd{Control-F} moves the cursor to the right non-destructively,
  39 \kbd{Control-B} moves the cursor to the left non-destructively, etc.).
  40
  41 An end-of-file on input is passed back as the string \code{'EOF'}.
  42
  43 An interpreter instance will recognize a command name \samp{foo} if
  44 and only if it has a method \method{do_foo()}.  As a special case,
  45 a line beginning with the character \character{?} is dispatched to
  46 the method \method{do_help()}.  As another special case, a line
  47 beginning with the character \character{!} is dispatched to the
  48 method \method{do_shell} (if such a method is defined).
  49
  50 All subclasses of \class{Cmd} inherit a predefined \method{do_help}.
  51 This method, called with an argument \code{bar}, invokes the
  52 corresponding method \method{help_bar()}.  With no argument,
  53 \method{do_help()} lists all available help topics (that is, all
  54 commands with corresponding \method{help_*()} methods), and also lists
  55 any undocumented commands.
  56 \end{methoddesc}
  57
  58 \begin{methoddesc}{onecmd}{str}
  59 Interpret the argument as though it had been typed in in
  60 response to the prompt.
  61 \end{methoddesc}
  62
  63 \begin{methoddesc}{emptyline}{}
  64 Method called when an empty line is entered in response to the prompt.
  65 If this method is not overridden, it repeats the last nonempty command
  66 entered.
  67 \end{methoddesc}
  68
  69 \begin{methoddesc}{default}{line}
  70 Method called on an input line when the command prefix is not
  71 recognized. If this method is not overridden, it prints an
  72 error message and returns.
  73 \end{methoddesc}
  74
  75 \begin{methoddesc}{precmd}{}
  76 Hook method executed just before the command line is interpreted, but
  77 after the input prompt is generated and issued.  This
  78 method is a stub in \class{Cmd}; it exists to be overridden by
  79 subclasses.
  80 \end{methoddesc}
  81
  82 \begin{methoddesc}{postcmd}{}
  83 Hook method executed just after a command dispatch is finished.  This
  84 method is a stub in \class{Cmd}; it exists to be overridden by
  85 subclasses.
  86 \end{methoddesc}
  87
  88 \begin{methoddesc}{preloop}{}
  89 Hook method executed once when \method{cmdloop()} is called.  This
  90 method is a stub in \class{Cmd}; it exists to be overridden by
  91 subclasses.
  92 \end{methoddesc}
  93
  94 \begin{methoddesc}{postloop}{}
  95 Hook method executed once when \method{cmdloop()} is about to return.
  96 This method is a stub in \class{Cmd}; it exists to be overridden by
  97 subclasses.
  98 \end{methoddesc}
  99
 100 Instances of \class{Cmd} subclasses have some public instance variables:
 101
 102 \begin{memberdesc}{prompt}
 103 The prompt issued to solicit input.
 104 \end{memberdesc}
 105
 106 \begin{memberdesc}{identchars}
 107 The string of characters accepted for the command prefix.
 108 \end{memberdesc}
 109
 110 \begin{memberdesc}{lastcmd}
 111 The last nonempty command prefix seen.
 112 \end{memberdesc}
 113
 114 \begin{memberdesc}{intro}
 115 A string to issue as an intro or banner.  May be overridden by giving
 116 the \method{cmdloop()} method an argument.
 117 \end{memberdesc}
 118
 119 \begin{memberdesc}{doc_header}
 120 The header to issue if the help output has a section for documented
 121 commands.
 122 \end{memberdesc}
 123
 124 \begin{memberdesc}{misc_header}
 125 The header to issue if the help output has a section for miscellaneous
 126 help topics (that is, there are \method{help_*()} methods without
 127 corresponding \method{do_*()} methods).
 128 \end{memberdesc}
 129
 130 \begin{memberdesc}{undoc_header}
 131 The header to issue if the help output has a section for undocumented
 132 commands (that is, there are \method{do_*()} methods without
 133 corresponding \method{help_*()} methods).
 134 \end{memberdesc}
 135
 136 \begin{memberdesc}{ruler}
 137 The character used to draw separator lines under the help-message
 138 headers.  If empty, no ruler line is drawn.  It defaults to
 139 \character{=}.
 140 \end{memberdesc}
 141
 142 \begin{memberdesc}{use_rawinput}
 143 A flag, defaulting to true.  If true, \method{cmdloop()} uses
 144 \function{raw_input()} to display a prompt and read the next command;
 145 if false, \function{sys.stdout.write()} and
 146 \function{sys.stdin.readline()} are used. (This means that by
 147 importing \module{readline}, on systems that support it, the
 148 interpreter will automatically support Emacs-like line editing
 149 and command-history keystrokes.)
 150 \end{memberdesc}