doc/expect.texi

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