我们在调试shell脚本的时候,不可以避免的会遇到问题,这个时候,假如我们可以跟踪到脚本到底是哪里问了问题,是哪个变量出了问题,这样就对我们的调试是很有帮助的,这里介绍一个shell里面的跟踪选项这里介绍的是set命令,假设在脚本里面加入set –x ,就能显示脚本运行是的冗余输出,如果在脚本文件中加入了命令set –x ,那么在set命令之后执行的每一条命令以及加载命令行中的任何参数都会显示出来,每一行都会加上加号(+),提示它是跟踪输出的标识,在子shell中执行的shell跟踪命令会加2个叫号(++)。

下面来看看演示脚本:

1:  [root@centos6 shell]# cat set-x.sh
2:  #!/bin/bash
3:  #set -x
4:  echo -n "Can you write device drivers?"
5:  read answer
6:  answer=$(echo $answer | tr [a-z] [A-Z])
7:  if [ $answer = Y ]
8:  then
9:          echo "Wow,you must be very skilled"
10:  else
11:          echo "Neither can I,I am just an example shell script"
12:  fi
13:  [root@centos6 shell]# sh set-x.sh
14:  Can you write device drivers?y
15:  Wow,you must be very skilled
16:  [root@centos6 shell]# sh set-x.sh
17:  Can you write device drivers?n
18:  Neither can I,I am just an example shell script
19:  [root@centos6 shell]#

 

上面的脚本内容里面,我吧set –x  这一行注释掉了,我们平时都是看到这种效果,下面我将把set –x 这个选项打开,来看看效果:

1:  [root@centos6 shell]# sh set-x.sh
2:  + echo -n 'Can you write device drivers?'
3:  Can you write device drivers?+ read answer
4:  y
5:  ++ echo y
6:  ++ tr '[a-z]' '[A-Z]'
7:  + answer=Y
8:  + '[' Y = Y ']'
9:  + echo 'Wow,you must be very skilled'
10:  Wow,you must be very skilled
11:  [root@centos6 shell]# sh set-x.sh
12:  + echo -n 'Can you write device drivers?'
13:  Can you write device drivers?+ read answer
14:  n
15:  ++ echo n
16:  ++ tr '[a-z]' '[A-Z]'
17:  + answer=N
18:  + '[' N = Y ']'
19:  + echo 'Neither can I,I am just an example shell script'
20:  Neither can I,I am just an example shell script
21:  [root@centos6 shell]#

 

 

   嘿嘿,看到了吧,每一行都显示出来,每一个参数的状态和执行到哪一步的值是多少,都可以看的很清楚了吧,我们可以很清楚的看到answer这个变量的每一步的状态和值,如果感兴趣,来试验下吧,这个选项