从字符串中准确捕获2个单词

Question

I'm using regex to parse a command that looks like this:

!hello foo bar

I would like to capture foo and bar. If the command is passed anything but 2 arguments then I want the regex to fail.

Here's my regex so far:

^!hello (.*)$

I know that {2} can be used to limit the amount captured, but I'm not sure exactly how to use it in this situation.

Thanks

Answer 1

Instead of the greedy (.*), I would recommend using something more specific like \w+ to match one or more "word" characters. Since whitespace may be insignificant, separate them with \s+. Rather than trying to use {2}, since you expect exactly two separated by whitespace, it is easier to spell each group out literally as \w+ with the whitespace requirement in between.

^!hello\s+(\w+)\s+(\w+)$

If you don't actually need to reuse the arguments, remove the ().

^!hello\s+\w+\s+\w+$

$pattern = '/^!hello\s+\w+\s+\w+$/';
echo preg_match($pattern, '!hello foo bar');
// 1
echo preg_match($pattern, '!hello foo bar baz');
// 0
echo preg_match($pattern, '!hello "foo bar" baz');
// 0
// Note a numeric argument matches \w+... If that isn't allowed
// you should use [A-Za-z]+ instead or just [a-z]+ and add the /i flag
echo preg_match($pattern, '!hello 123 baz');
// 1
echo preg_match($pattern, '!hello a$1 baz');
// 0