Exploring Expect

Matching A Null

By default, nulls (bytes with value zero) are automatically stripped from the spawned process output. This can be disabled by setting the integer variable exp_remove_nulls to 0 and reenabled by setting it to 1.

Once null stripping is disabled, nulls can be matched using exp_null. A string-style pattern is still passed, but it is only used for bookkeeping and debugging. For example:

exp_expectl(fd,
    exp_null, "zero byte", 1,
    exp_end);