doc/ref/expect.texi

   1 @c -*-texinfo-*-
   2 @c This is part of the GNU Guile Reference Manual.
   3 @c Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004
   4 @c   Free Software Foundation, Inc.
   5 @c See the file guile.texi for copying conditions.
   6
   7 @node Expect
   8 @section Expect
   9
  10 The macros in this section are made available with:
  11
  12 @lisp
  13 (use-modules (ice-9 expect))
  14 @end lisp
  15
  16 @code{expect} is a macro for selecting actions based on the output from
  17 a port.  The name comes from a tool of similar functionality by Don Libes.
  18 Actions can be taken when a particular string is matched, when a timeout
  19 occurs, or when end-of-file is seen on the port.  The @code{expect} macro
  20 is described below; @code{expect-strings} is a front-end to @code{expect}
  21 based on regexec (see the regular expression documentation).
  22
  23 @defmac expect-strings clause @dots{}
  24 By default, @code{expect-strings} will read from the current input port.
  25 The first term in each clause consists of an expression evaluating to
  26 a string pattern (regular expression).  As characters
  27 are read one-by-one from the port, they are accumulated in a buffer string
  28 which is matched against each of the patterns.  When a
  29 pattern matches, the remaining expression(s) in
  30 the clause are evaluated and the value of the last is returned.  For example:
  31
  32 @lisp
  33 (with-input-from-file "/etc/passwd"
  34   (lambda ()
  35     (expect-strings
  36       ("^nobody" (display "Got a nobody user.\n")
  37                  (display "That's no problem.\n"))
  38       ("^daemon" (display "Got a daemon user.\n")))))
  39 @end lisp
  40
  41 The regular expression is compiled with the @code{REG_NEWLINE} flag, so
  42 that the ^ and $ anchors will match at any newline, not just at the start
  43 and end of the string.
  44
  45 There are two other ways to write a clause:
  46
  47 The expression(s) to evaluate
  48 can be omitted, in which case the result of the regular expression match
  49 (converted to strings, as obtained from regexec with match-pick set to "")
  50 will be returned if the pattern matches.
  51
  52 The symbol @code{=>} can be used to indicate that the expression is a
  53 procedure which will accept the result of a successful regular expression
  54 match.  E.g.,
  55
  56 @lisp
  57 ("^daemon" => write)
  58 ("^d(aemon)" => (lambda args (for-each write args)))
  59 ("^da(em)on" => (lambda (all sub)
  60                   (write all) (newline)
  61                   (write sub) (newline)))
  62 @end lisp
  63
  64 The order of the substrings corresponds to the order in which the
  65 opening brackets occur.
  66
  67 A number of variables can be used to control the behaviour
  68 of @code{expect} (and @code{expect-strings}).
  69 Most have default top-level bindings to the value @code{#f},
  70 which produces the default behaviour.
  71 They can be redefined at the
  72 top level or locally bound in a form enclosing the expect expression.
  73
  74 @table @code
  75 @item expect-port
  76 A port to read characters from, instead of the current input port.
  77 @item expect-timeout
  78 @code{expect} will terminate after this number of
  79 seconds, returning @code{#f} or the value returned by expect-timeout-proc.
  80 @item expect-timeout-proc
  81 A procedure called if timeout occurs.  The procedure takes a single argument:
  82 the accumulated string.
  83 @item expect-eof-proc
  84 A procedure called if end-of-file is detected on the input port.  The
  85 procedure takes a single argument: the accumulated string.
  86 @item expect-char-proc
  87 A procedure to be called every time a character is read from the
  88 port.  The procedure takes a single argument: the character which was read.
  89 @item expect-strings-compile-flags
  90 Flags to be used when compiling a regular expression, which are passed
  91 to @code{make-regexp} @xref{Regexp Functions}.  The default value
  92 is @code{regexp/newline}.
  93 @item expect-strings-exec-flags
  94 Flags to be used when executing a regular expression, which are
  95 passed to regexp-exec @xref{Regexp Functions}.
  96 The default value is @code{regexp/noteol}, which prevents @code{$}
  97 from matching the end of the string while it is still accumulating,
  98 but still allows it to match after a line break or at the end of file.
  99 @end table
 100
 101 Here's an example using all of the variables:
 102
 103 @smalllisp
 104 (let ((expect-port (open-input-file "/etc/passwd"))
 105       (expect-timeout 1)
 106       (expect-timeout-proc
 107         (lambda (s) (display "Times up!\n")))
 108       (expect-eof-proc
 109         (lambda (s) (display "Reached the end of the file!\n")))
 110       (expect-char-proc display)
 111       (expect-strings-compile-flags (logior regexp/newline regexp/icase))
 112       (expect-strings-exec-flags 0))
 113    (expect-strings
 114      ("^nobody"  (display "Got a nobody user\n"))))
 115 @end smalllisp
 116 @end defmac
 117
 118 @defmac expect clause @dots{}
 119 @code{expect} is used in the same way as @code{expect-strings},
 120 but tests are specified not as patterns, but as procedures.  The
 121 procedures are called in turn after each character is read from the
 122 port, with two arguments: the value of the accumulated string and
 123 a flag to indicate whether end-of-file has been reached.  The flag
 124 will usually be @code{#f}, but if end-of-file is reached, the procedures
 125 are called an additional time with the final accumulated string and
 126 @code{#t}.
 127
 128 The test is successful if the procedure returns a non-false value.
 129
 130 If the @code{=>} syntax is used, then if the test succeeds it must return
 131 a list containing the arguments to be provided to the corresponding
 132 expression.
 133
 134 In the following example, a string will only be matched at the beginning
 135 of the file:
 136
 137 @lisp
 138 (let ((expect-port (open-input-file "/etc/passwd")))
 139   (expect
 140      ((lambda (s eof?) (string=? s "fnord!"))
 141         (display "Got a nobody user!\n"))))
 142 @end lisp
 143
 144 The control variables described for @code{expect-strings} also
 145 influence the behaviour of @code{expect}, with the exception of
 146 variables whose names begin with @code{expect-strings-}.
 147 @end defmac