Exploring Expect

The—And Other Flags

In Chapter 3 (p. 72), I mentioned the #! line with "—" at the end. I did not explain it at the time, but most of the scripts so far have used this line. I described the #! earlier in this chapter. Now I will explain "—“. The "—" is a flag to Expect. It says not to interpret any of the script arguments but just to pass them on to the script. This is comparable to saying:

expect—script args

Without the "—“, Expect itself interprets arguments that look likeflags. Arguments that look like flags begin with a "-" and appear before arguments that do not look like flags. What is important here is that after Expect finds an argument that does not look like a flag, then no other argument can be a flag. I will discuss this more later.

Flags that Expect knows about are:

-b	read the script a line at a time (i.e., unbuffered)
-ccmd	execute this command before any in the script
-ffile	read commands from this file
-d	print internal (diagnostic) information
-D	enable the debugger
−i	run interactively
-n	do not source ∼/.expect.rc
-N	do not source $expect_library/expect.rc
-	read commands from the standard input
—	do not interpret remaining arguments

Some flags take arguments. These can be run together with the flag itself, but for consistency I always put a space between them. For the sake of accuracy, the term flag includes both the dash, letter, and any arguments.

In the following sections, I will describe each of these flags in detail.