如何形成正则表达式以识别变量名的正确声明 [英] How to form a regex to recognize correct declaration of variable names

问题描述

我想组成一个正则表达式ro来识别变量名的声明.用户将输入他们想要的字符串作为变量名，程序必须检查该变量是否有效.

I would like to form a regex ro recognize the declaration of a variable name. User will enter a string that they would like as a variable name, and the program has to check whether the variable is valid.

1. 变量名称的第一个字符必须是字母或下划线.它不能以数字开头.
2. 变量名中不允许使用逗号和空格.
3. 变量名中除下划线外不允许使用其他特殊符号.

我整天都在尝试，但没有得到正确的答案.

I have been trying for the whole day and couldn't get the correct one.

推荐答案

我们要做的第一件事是收集第一个字符的所有有效字符的列表:

First thing we do is gather a list of all the valid characters for the first character:

[a-zA-Z_$]

然后是其他字符:

[a-zA-Z_$0-9]

我们要匹配整个字符串，并且可以有0个或多个其他字符，因此正则表达式变为:

we want to match the whole string, and we can have 0 or more of the other characters, so the regex becomes:

^[a-zA-Z_$][a-zA-Z_$0-9]*$

我允许在正则表达式的第一个字符(以及美元符号)中使用大写字母，因为这是对有效性的测试，而不是对格式正确的变量的测试.(请注意，常量应该大写，包括首字母.)

I allow capital characters in the first character in the regex (as well as dollar signs), because this is a test for validity, not for well-formed variables. (Note that constants should be in all caps, including the first letter.)

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