本篇內容介紹了“shell腳本中case條件控制語句的使用”的有關知識，在實際案例的操作過程中，不少人都會遇到這樣的困境，接下來就讓小編帶領大家學習一下如何處理這些情況吧！希望大家仔細閱讀，能夠學有所成！

在shell腳本中，發現case語句的一個問題。
就是指定小寫字母[a-z]和大寫字母[A-Z]的這種方法不管用了。

出現如下情況：

代碼如下:

[root@station1 ~]# cat case.sh
#!/bin/bash
while :
do
echo -n "input a letter: "
read var
case "$var" in
  [a-z]) echo "Lowercase letter";;
  [A-Z]) echo "Uppercase letter";;
 [0-9]) echo "Digit";;
  *) echo "Punctuation, whitespace, or other";;
esac
done
[root@station1 ~]# bash case.sh
input a letter: a
Lowercase letter
input a letter: A
Lowercase letter
input a letter: 2
Digit
input a letter: 0
Digit
input a letter: B
Lowercase letter
input a letter: y
Lowercase letter
input a letter: ^C
[root@station1 ~]#

可以看到當輸入大小寫字母都會輸出“Lowercase letter”

就當我疑惑不解的時候，奇跡發生了。。。。

代碼如下:

[root@station1 ~]# bash case.sh
input a letter: Z
Uppercase letter
input a letter:

當輸入大寫Z的時候，終于出現了我們想要的結果：Uppercase letter
后來在man bash文檔中也沒有關于"-"代表范圍的說明，值說想匹配"-"，就把"-"放到[]中最前面或者最后面。
case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
A case command first expands word, and tries to match it against each pattern in turn, using the same matching rules as for pathname
expansion (see Pathname Expansion below). The word is expanded using tilde expansion, parameter and variable expansion, arithmetic sub-
stitution, command substitution, process substitution and quote removal. Each pattern examined is expanded using tilde expansion, param-
eter and variable expansion, arithmetic substitution, command substitution, and process substitution. If the shell option nocasematch is
enabled, the match is performed without regard to the case of alphabetic characters. When a match is found, the corresponding list is
executed. If the ;; operator is used, no subsequent matches are attempted after the first pattern match. Using ;& in place of ;; causes
execution to continue with the list associated with the next set of patterns. Using ;;& in place of ;; causes the shell to test the next
pattern list in the statement, if any, and execute any associated list on a successful match. The exit status is zero if no pattern
matches. Otherwise, it is the exit status of the last command executed in list.

再看下面這段代碼：

代碼如下:

[root@station1 ~]# cat case.sh
#!/bin/bash
while :
do
echo -n "input a letter: "
read var
case "$var" in
[a-c]) echo "Lowercase letter";;
[A-Z]) echo "Uppercase letter";;
[0-9]) echo "Digit";;
*) echo "Punctuation, whitespace, or other";;
esac
done
[root@station1 ~]# bash case.sh
input a letter: a
Lowercase letter
input a letter: b
Lowercase letter
input a letter: c
Lowercase letter
input a letter: d
Uppercase letter
input a letter: e
Uppercase letter
input a letter: ^C
[root@station1 ~]#

可以看出來它的編碼方式是：aAbBcCdDeE...yYzZ
所以才會出現這種情況。這也算是一個小bug吧，如果想真的想達到我們想要的結果，可以用posix的[:upper:]。
個人想法：有時候出現這種情況也不是個壞事，或許還可以利用這個bug去做點事。

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