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 $lockfileelse echo /"COOLID: $coolid/" > $lockfile echo DONE!fi/r"sleep 1 ;# necessaryexpect { 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!> fiCOOLID: 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!> fiCOOLID: 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。