expect_out(buffer)中包含send的数据
我一直以为在Expect中一旦执行send之后，expect_out(buffer)就会被清空，直到有新的数据被填入，而恰恰就是这些数据被用在expect语句中。而今天在调试时发现的问题却令我大吃一惊，原来expect_out(buffer)不会被自动清空，而expect到的数据很可能不是你真正想要的，非常有可能是历史数据。"expect_out(buffer) has the content of the previous send" 一文也指出了这个问题。
比如在我的代码中，有如下片段：
set prompt "#"
set lockfile "/root/tmp/.cool.lock"
send "
if /[ -e $lockfile ]; then
cat $lockfile
else
echo /"COOLID: $coolid/" > $lockfile
echo DONE!
fi
/r"
sleep 1 ;# necessary
expect {
timeout {
puts stderr "WARNING: $ME: cannot verify if the Linux AP is locked by other COOL session!";
exit 2;
}
-re "COOLID: (/[1-9](/[0-9])*).*$prompt" {
puts stdout "expect_out(buffer)=$expect_out(buffer)"
puts stdout "expect_out(0,string)=$expect_out(0,string)"
puts stdout "expect_out(1,string)=$expect_out(1,string)"
puts stdout "expect_out(2,string)=$expect_out(2,string)"
puts stdout "expect_out(3,string)=$expect_out(3,string)"
}
"DONE!" ;# do nothing
}
无论$lockfile是否存在，expect总会得到COOLID: 68，而expect_out(buffer)的出如下：
[root@bjvsmcl05 ~]# expect_out(buffer)= Last login: Fri Jul 23 09:32:13 2010 from bjbldd [root@bjvsmcl05 ~]# [root@bjvsmcl05 ~]# if [ -e /root/tmp/.cool.lock ]; then > cat /root/tmp/.cool.lock > else > echo "COOLID: 68" > /root/tmp/.cool.lock > echo DONE! > fi COOLID: 1234 [root@bjvsmcl05 ~]# [root@bjvsmcl05 ~]# expect_out(0,string)=23 09:32:13 2010 from bjbldd [root@bjvsmcl05 ~]# [root@bjvsmcl05 ~]# if [ -e /root/tmp/.cool.lock ]; then > cat /root/tmp/.cool.lock > else > echo "COOLID: 68" > /root/tmp/.cool.lock > echo DONE! > fi COOLID: 1234
由此可见，由于expect_out(buffer)中含有send的echo "COOLID: 68"，因此永远都能匹配到这个数据。
由于没有找到一种可以清空expect_out(buffer)的方法，无法实时地将expect_out(buffer)清空。我能想到的解决方法有两种：一是更改send和expect的内容或方式，避免send的内容中出现expect的模式(pattern)。比如在我的程序中把上述代码段改为：
set lockfile "/root/tmp/.cool.lock"
send "cat $lockfile/r"
expect {
-re "COOLID: (/[1-9](/[0-9])*)" {
puts stdout "expect_out(buffer)=$expect_out(buffer)"
puts stdout "expect_out(0,string)=$expect_out(0,string)"
puts stdout "expect_out(1,string)=$expect_out(1,string)"
if { [string compare $expect_out(1,string) $coolid] } {
puts stdout "ERROR: $ME: $pcname has been reserverd by COOL session $expect_out(1,string), please choose another Linux PC instead./n"
exit 2;
}
}
"cat: $lockfile: No such file or directory*" {
send "echo /"COOLID: $coolid/" > $lockfile/r"
}
}
就可以正常工作了。
另一种方法是按照"expect_out(buffer) has the content of the previous send"的例子中的方法，set prompt，保持原始代码中send的内容不变，将expect的正则表达式改为 -re "fi(.*)$prompt"，如此一来希望的输出就在expect_out(1,string)中了，然后利用string或者lsearch命令对匹配到的数据进行分析。
结论：今后在编写Expect脚本时，不仅要考虑每一步的send/expect，也还要考虑到这一步的expect的内容有可能出现在之前的历史数据中。