正则表达式匹配子字符串，但不以某些字符开头

Question

I am searching for a substring eg test , in a longer string eg alongstringtest .

In this example it would match ok

but I want to exclude certain cases ( when 'test' preceded by certain characters)

eg

do not match 'a-test' (because of '-' )

do not match 'abcgtest' (because of 'g' )

do not match 'abc"test' (because of '"' )

I haven't written any regex for a long time, so this has me pulling my hair out abit !

Answer 1

使用负面回顾：

(?<![-g"])test

Answer 2

The simplest answer is

/(?<![g"-])test/

But there is room for optimization if you need more performance. If test can't appear at the very start of the string, then the following is a clear winner in terms of simplicity and performance:

/[^g"-]test/

Otherwise, I'd try the following:

/test(?<![g"-].{4})/s

/^test|[^g"-]test/

/^test/ || /[^g"-]test/

Note: - can have special meaning in character classes, but not if it's the first character, the first character after the negating ^ , or the last character. I always use it last; it keeps things nice and simple.