为什么 shell case 语句中的第一个模式不能是多重模式？
案例的标准描述声明说：
The format for the case construct is as follows:
case word in
[(]pattern1) compound-list;;
[[(]pattern[ | pattern] ... ) compound-list;;] ...
[[(]pattern[ | pattern] ... ) compound-list]
esac
The ";;" is optional for the last compound-list.
为什么 pattern1 不能也是多重模式？这看起来相当随意，尽管我很确定它一定不是这样。
谢谢！
The standard description of the case statement says:
The format for the case construct is as follows:
case word in
[(]pattern1) compound-list;;
[[(]pattern[ | pattern] ... ) compound-list;;] ...
[[(]pattern[ | pattern] ... ) compound-list]
esac
The ";;" is optional for the last compound-list.
Why can't be pattern1 be a multiple pattern as well? It seems rather arbitrary, though I'm pretty sure it must not be.
Thanks!
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我认为你误解了他们的意思。您链接到的页面上的语法没有显示这样的区别：
case_clause : Case WORD linebreak in linebreak case_list Esac | Case WORD linebreak in linebreak case_list_ns Esac | Case WORD linebreak in linebreak Esac ; case_list_ns : case_list case_item_ns | case_item_ns ; case_list : case_list case_item | case_item ; case_item_ns : pattern ')' linebreak | pattern ')' compound_list linebreak | '(' pattern ')' linebreak | '(' pattern ')' compound_list linebreak ; case_item : pattern ')' linebreak DSEMI linebreak | pattern ')' compound_list DSEMI linebreak | '(' pattern ')' linebreak DSEMI linebreak | '(' pattern ')' compound_list DSEMI linebreak ; pattern : WORD /* Apply rule 4 */ | pattern '|' WORD /* Do not apply rule 4 */I think you're misinterpreting what they're saying. The grammar on the page you link to does not show such a distinction:
case_clause : Case WORD linebreak in linebreak case_list Esac | Case WORD linebreak in linebreak case_list_ns Esac | Case WORD linebreak in linebreak Esac ; case_list_ns : case_list case_item_ns | case_item_ns ; case_list : case_list case_item | case_item ; case_item_ns : pattern ')' linebreak | pattern ')' compound_list linebreak | '(' pattern ')' linebreak | '(' pattern ')' compound_list linebreak ; case_item : pattern ')' linebreak DSEMI linebreak | pattern ')' compound_list DSEMI linebreak | '(' pattern ')' linebreak DSEMI linebreak | '(' pattern ')' compound_list DSEMI linebreak ; pattern : WORD /* Apply rule 4 */ | pattern '|' WORD /* Do not apply rule 4 */