Matching Multiple Times
Many tasks require an expect
to be repeated some number of times. Reading files from a list is an example of this. In the example on page 133, I matched a single line with the command:
expect "(\[^\r]*)\r\n"
This can be wrapped in a loop to read multiple lines and break when a prompt appears:
while 1 { expect { "(\[^\r]*)\r\n" process_line $prompt break } }
This version has additional patterns upon which to break out of the loop:
while 1 { expect { "(\[^\r]*)\r\n" process_line eof { handle_eof break } timeout { handle_timeout break } $prompt break } }
Here, handle_eof
and handle_timeout
are imaginary procedures that perform some processing appropriate to the condition. More importantly, notice that all of the patterns but one terminate by breaking out of the loop. It is possible to simplify this by using the exp_continue
command.
When executed as an expect
action, the command exp_continue
causes control to be continued inside the current expect
command. expect
continues trying to match the pattern, but from where it left off after the previous match. expect
effectively repeats its search as if it had been invoked again.
Since expect
does not have to be explicitly reinvoked, the while
command is not necessary. The previous example can thus be rewritten as:
expect { "(\[^\r]*)\r" { process_line exp_continue } eof handle_eof timeout handle_timeout $prompt }
In this example, each line is matched and then processed via process_line
. expect
then continues to search ...
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