The Value Of spawn_id Affects Many Commands
The chess
and write
scripts are good examples of how spawn_id
affects both the send
and expect
commands. To recap, send
and expect
communicate with the currently spawned process—that is, the process whose spawn id is stored in the variable spawn_id
. Other commands that are affected by spawn_id
include interact
, close
, wait
, match_max
, parity
, and remove_nulls
. In later chapters, I will describe still more commands that are affected by spawn_id
.
As an example, here is a code fragment to close
and wait
on a list of spawn ids.
foreach spawn_id $spawn_ids { close wait }
This loop could have been added to the earlier write
script—except that the script effectively does the close
and wait
upon exit anyway. However, remember from Chapter 4 (p. 103) that programs that run in raw mode (such as telnet
) often need explicit code to force them to exit. That code might be appropriate in such a loop.
Imagine writing a script that telnet
s to several hosts and simultaneously sends the same keystrokes to each of them. This script could be used, for example, to reboot a set of machines, change passwords, test functionality, or any number of things that have to be performed directly on each machine.
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