Exploring Expect

When The Number Of Patterns Is Not Known In Advance

The exp_expectl function is appropriate when the list of patterns is known in advance. At a minimum, the number of patterns must be known in advance.

When the number of patterns can vary, the function exp_fexpectv is more suitable. This function is called with only two arguments. The first is a file descriptor. The second is an array of pattern descriptors. The prototype is:

int exp_expectv(int fd, struct exp_case *pats);

struct exp_case is defined as follows:

struct exp_case {
    char *pattern;
    regexp *re;
    enum exp_type type;
    int value;
};

The information in an exp_case structure is exactly the same information that was passed as the direct arguments in exp_expectl. The pattern is stored in pattern. An optional compiled regular expression is stored in re. The type element describes the type of pattern and is an exp_type enumeration constant (see page 495). As before, the final pattern type must be exp_end. Finally, value is the integer returned when the associated pattern matches.

exp_expectv works slightly differently than exp_expectl when the pattern type is exp_regexp. In this case, exp_expectv compiles each pattern and stores the compiled form in re. The compiled form is left accessible in the exp_case structure for your use or reuse if exp_expectv is recalled with the same patterns. If the type is exp_regexp, then exp_expectv checks if re is initialized before compiling the pattern. The pattern is compiled only if re is not initialized. ...