What Happens When Input Does Not Match
Once expect
has matched data to a pattern, it moves the data to the expect_out
variable as I showed earlier. The matched data is no longer eligible to be matched. Additional matches can only take place with new data.
Consider the following fragment:
expect "hi" send "$expect_out(0,string) $expect_out(buffer)"
If I execute these two commands, Expect waits for me to enter hi
. If I enter philosophic
followed by a return, Expect finds the hi
and prints:
hi phi
If I execute the two commands again, Expect prints:
hi losophi
Even though there were two occurrences of hi
, the first time expect
matched the first one, moving it into expect_out
. The next expect
started from where the previous one had left off.
With simple patterns like these, expect
always stops waiting and returns immediately after matching the pattern. If expect
receives more input than it needs, that input is remembered for the possibility of matching in later expect
commands. In other words, expect
buffers its input. This allows expect
to receive input before it is actually ready to use it. The input will be held in an input buffer until an expect
pattern matches it. This buffer is internal to expect
and is not accessible to the script in any way except by matching patterns against it.
After the second expect
above, the buffer must hold c\n
. This is all that was left after the second hi
in philosophic
. The \n
is there, of course, because after entering the word, I pressed return.
What ...
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