匹配字符串中的排他搜索组

Question

I've been struggling to come up with a reg-ex fix within my pg-promise library...

It implements a formatting method which does a verification for a string to determine whether it is a simple one or not, based on the following rules:

The string is defined as simple when:

• it is a same-case single word, without spaces
• it can contain underscores, and can even start with them
• it can contain digits and $, but cannot start with those

Those a basically the rules for determining when an SQL alias needs to be wrapped in double-quotes or not.

So if I isolate the test logic:

const m = name.match(/[a-z_][a-z0-9_$]*|[A-Z_][A-Z0-9_$]*/);

console.log(m && m[0] === name ? 'simple' : 'complex');

It passes tests in all cases, except when we have an underscore and then capital letters, like this: _A or __ABC . At the same time, it works for _a and __abc .

How to change the regular expression to make it work for those special cases also?

Thank you!

Answer 1

If you add metacharacters ^ (beginning of the string) and $ (end of the string) to your regular expression, it will work as expected for uppercase words too, and also let simplify condition on output:

const m = name.match(/^([a-z_][a-z0-9_$]*|[A-Z_][A-Z0-9_$]*)$/);

console.log(m ? 'simple' : 'complex');