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@c -*-texinfo-*-
@c This is part of the GNU Guile Reference Manual.
@c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004
@c Free Software Foundation, Inc.
@c See the file guile.texi for copying conditions.
@node Expect
@section Expect
The macros in this section are made available with:
@lisp
(use-modules (ice-9 expect))
@end lisp
@code{expect} is a macro for selecting actions based on the output from
a port. The name comes from a tool of similar functionality by Don Libes.
Actions can be taken when a particular string is matched, when a timeout
occurs, or when end-of-file is seen on the port. The @code{expect} macro
is described below; @code{expect-strings} is a front-end to @code{expect}
based on regexec (see the regular expression documentation).
@defmac expect-strings clause @dots{}
By default, @code{expect-strings} will read from the current input port.
The first term in each clause consists of an expression evaluating to
a string pattern (regular expression). As characters
are read one-by-one from the port, they are accumulated in a buffer string
which is matched against each of the patterns. When a
pattern matches, the remaining expression(s) in
the clause are evaluated and the value of the last is returned. For example:
@lisp
(with-input-from-file "/etc/passwd"
(lambda ()
(expect-strings
("^nobody" (display "Got a nobody user.\n")
(display "That's no problem.\n"))
("^daemon" (display "Got a daemon user.\n")))))
@end lisp
The regular expression is compiled with the @code{REG_NEWLINE} flag, so
that the ^ and $ anchors will match at any newline, not just at the start
and end of the string.
There are two other ways to write a clause:
The expression(s) to evaluate
can be omitted, in which case the result of the regular expression match
(converted to strings, as obtained from regexec with match-pick set to "")
will be returned if the pattern matches.
The symbol @code{=>} can be used to indicate that the expression is a
procedure which will accept the result of a successful regular expression
match. E.g.,
@lisp
("^daemon" => write)
("^d(aemon)" => (lambda args (for-each write args)))
("^da(em)on" => (lambda (all sub)
(write all) (newline)
(write sub) (newline)))
@end lisp
The order of the substrings corresponds to the order in which the
opening brackets occur.
A number of variables can be used to control the behaviour
of @code{expect} (and @code{expect-strings}).
Most have default top-level bindings to the value @code{#f},
which produces the default behaviour.
They can be redefined at the
top level or locally bound in a form enclosing the expect expression.
@table @code
@item expect-port
A port to read characters from, instead of the current input port.
@item expect-timeout
@code{expect} will terminate after this number of
seconds, returning @code{#f} or the value returned by expect-timeout-proc.
@item expect-timeout-proc
A procedure called if timeout occurs. The procedure takes a single argument:
the accumulated string.
@item expect-eof-proc
A procedure called if end-of-file is detected on the input port. The
procedure takes a single argument: the accumulated string.
@item expect-char-proc
A procedure to be called every time a character is read from the
port. The procedure takes a single argument: the character which was read.
@item expect-strings-compile-flags
Flags to be used when compiling a regular expression, which are passed
to @code{make-regexp} @xref{Regexp Functions}. The default value
is @code{regexp/newline}.
@item expect-strings-exec-flags
Flags to be used when executing a regular expression, which are
passed to regexp-exec @xref{Regexp Functions}.
The default value is @code{regexp/noteol}, which prevents @code{$}
from matching the end of the string while it is still accumulating,
but still allows it to match after a line break or at the end of file.
@end table
Here's an example using all of the variables:
@smalllisp
(let ((expect-port (open-input-file "/etc/passwd"))
(expect-timeout 1)
(expect-timeout-proc
(lambda (s) (display "Times up!\n")))
(expect-eof-proc
(lambda (s) (display "Reached the end of the file!\n")))
(expect-char-proc display)
(expect-strings-compile-flags (logior regexp/newline regexp/icase))
(expect-strings-exec-flags 0))
(expect-strings
("^nobody" (display "Got a nobody user\n"))))
@end smalllisp
@end defmac
@defmac expect clause @dots{}
@code{expect} is used in the same way as @code{expect-strings},
but tests are specified not as patterns, but as procedures. The
procedures are called in turn after each character is read from the
port, with two arguments: the value of the accumulated string and
a flag to indicate whether end-of-file has been reached. The flag
will usually be @code{#f}, but if end-of-file is reached, the procedures
are called an additional time with the final accumulated string and
@code{#t}.
The test is successful if the procedure returns a non-false value.
If the @code{=>} syntax is used, then if the test succeeds it must return
a list containing the arguments to be provided to the corresponding
expression.
In the following example, a string will only be matched at the beginning
of the file:
@lisp
(let ((expect-port (open-input-file "/etc/passwd")))
(expect
((lambda (s eof?) (string=? s "fnord!"))
(display "Got a nobody user!\n"))))
@end lisp
The control variables described for @code{expect-strings} also
influence the behaviour of @code{expect}, with the exception of
variables whose names begin with @code{expect-strings-}.
@end defmac
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