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shell腳本中case條件控制語句的一個bug分析

更新時間：2013年11月07日 17:38:26 作者：

在shell腳本中，發(fā)現(xiàn)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

在shell腳本中，發(fā)現(xiàn)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(xiàn)如下情況：

[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(dāng)輸入大小寫字母都會輸出“Lowercase letter”

就當(dāng)我疑惑不解的時候，奇跡發(fā)生了。。。。

復(fù)制代碼代碼如下:

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

當(dāng)輸入大寫Z的時候，終于出現(xiàn)了我們想要的結(jié)果：Uppercase letter
后來在man bash文檔中也沒有關(guān)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：

復(fù)制代碼代碼如下:

[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(xiàn)這種情況。這也算是一個小bug吧，如果想真的想達(dá)到我們想要的結(jié)果，可以用posix的[:upper:]。
個人想法：有時候出現(xiàn)這種情況也不是個壞事，或許還可以利用這個bug去做點(diǎn)事。

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