設定除錯選項概覽

我們在除錯shell指令碼的時候，不可以避免的會遇到問題，這個時候，假如我們可以跟蹤到指令碼到底是哪裡問了問題，是哪個變量出了問題，這樣就對我們的除錯是很有幫助的，這裡介紹一個shell裡面的跟蹤選項這裡介紹的是set命令，假設在腳本里面加入set –x ,就能顯示指令碼執行是的冗餘輸出，如果在指令碼檔案中加入了命令set –x ，那麼在set命令之後執行的每一條命令以及載入命令列中的任何引數都會顯示出來，每一行都會加上加號（+），提示它是跟蹤輸出的標識，在子shell中執行的shell跟蹤命令會加2個叫號（++）。

下面來看看演示指令碼：

   1:  [[email protected] 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:  [[email protected] shell]# sh set-x.sh

  14:  Can you write device drivers?y

  15:  Wow,you must be very skilled

  16:  [[email protected] shell]# sh set-x.sh

  17:  Can you write device drivers?n

  18:  Neither can I,I am just an example shell script

  19:  [[email protected] shell]#

上面的指令碼內容裡面，我吧set –x  這一行註釋掉了，我們平時都是看到這種效果，下面我將把set –x 這個選項開啟，來看看效果：

   1:  [[email protected] 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:  [[email protected] 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:  [[email protected] shell]#

   嘿嘿，看到了吧，每一行都顯示出來，每一個引數的狀態和執行到哪一步的值是多少，都可以看的很清楚了吧，我們可以很清楚的看到answer這個變數的每一步的狀態和值，如果感興趣，來試驗下吧，這個選項