在其他两个字符串之间找到某些东西之后找到一个字符串

Question

Let's go with an example:

"Blablabla. My name is John and I'm 21 years old. Blablabla"

Other example:

"Blablabla. My name is John and I'm 21 years old. - Hi I'm Mary and I'm 22 years old."

Basically, I want to match the age of the first person (here, 21, it could be 23 or whatever). The idea is that I know I'll have a sentence beginning with "My name is $name and I'm 21" but I can't afford to know what is $name. The gross idea is to select a number after "My name is "+something+" and I'm ".

How one would do that with a regex, knowing that I can't use catch groups?

What I have so far:

    (?<=<My name is )(.*)(?= years old)

Ideally I would like something like that to work:

    (?<=<My name is .* and I'm )(.*)(?= years old)

... but it does not! .* can't be in a look ahead group apparently (which makes some sense).

Thank you kindly.

Answer 1

/My name is (\w+) and I'm (\d+) years old./

Now the first matched group is the name, the second matched group is the age.

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If for some reason you don't want to use groups, you can match:

/(?<= and I'm )\d+(?= years old.)/

for the name and:

 /(?<= and I'm )\\d+(?= years old.)/ 

for the age.

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As you have noticed, lookbehinds with variable length are not allowed (at least in the regex engines that I know of, not that it is logically impossible). However, you can use \\K as an alternative:

 /My name is \\w+ and I'm \\K\\d+(?= years old.)/ 

Answer 2

@ndn's answer is basically correct, but I think it needs a couple of modifications:

1. The \\w+ expression will not find spaces, such as in "My name is Mary Kate and I'm 47 years old."
2. If I'm interpret your request correctly that you need only the date to match, then I don't think the lookbehind and lookaround assertions that you and @ndn have set up are necessary.

I believe this regex will give you what you want:
My name is .+? and I'm (\\d+) years old\\.

(Note the \\. at the end so it will match the literal period, rather than any character.)

See example at https://regex101.com/r/nJ7wS5/1