正则表达式匹配多个子字符串

Question

I have written a regular expression to test how a string is a logical expression or not. Here is the regular expression:

/(.*)(<|>|<=|>=|=|!=)(.*)/

And here is the subject which I tested with the expression above:

3!=2

The preg_match_all function in PHP return the following array:

[
  [
    "3!=2"
  ],
  [
    null
  ],
  [
    "="
  ],
  [
    "2"
  ]
]

I got a wrong logical operator because it's not match only the = pattern but also match the != operator. How should I rewrite the regular expression to not match multiple strings in the brackets?

Answer 1

You should exclude <>! before the operator and = after operator. Then, just to shorten, group the operators tighter.

([^<>!]*)([<>]=?|!?=)([^=]*)

You could also shorten it a bit with this:

(\w+)([<>]=?|!?=)(\w+)

---

With <=> , use

([^<>!]*)(<=>|[<>]=?|!?=)([^=>]*)

or, better yet in some cases,

(\w+)(<=>|[<>]=?|!?=)(\w+)

Answer 2

The .* is eating the ! . Make the .* specific to the operators you don't want it to match. I think:

([^!<>=]+)(<|>|<=|>=|!=|=)(.*)

Should do it.

Demo: https://regex101.com/r/yM5aY8/1

or if you are only work with numbers just use \\d+ .

Demo2: https://regex101.com/r/yM5aY8/2

Answer 3

如果表达式的两边都有数字/变量名，那么在开头和结尾只使用。*而不是'\\ w。*'

(\w.*)(<|>|<=|>=|=|!=)(\w.*)