doc/ref/expect.texi

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