正则表达式 - 当它在 php 中找到第二次出现的字符时返回字符串的一部分说“$”

Question

Here i am having a string "one two $\\alpha \\beta $ three" .

What i need is to get the part of string until its second occurrence of a character here it is "$" or may be group of characters "$$" .

ie, output should be "one two $\\alpha \\beta $" and "one two $$\\alpha \\beta $$" if the string is "one two $$\\alpha \\beta $$ three" .

Answer 1

Using the regex /.*\\$.*\\$/ will give you what you want.

This code

$ptrn='/.*\$.*\$/';
preg_match_all($ptrn, "one two $\alpha \beta $ three", $matches);  
echo $matches[0][0] . "<br>";
preg_match_all($ptrn, "one two $$\alpha \beta $$ three", $matches);  
echo $matches[0][0] . "<br>";

will give the following output

one two $\alpha \beta $
one two $$\alpha \beta $$

So I guess that's what you want. Or...?

Regards

Answer 2

Solution with preg_match function:

$str = "one two $\alpha \beta $ three one two $$\alpha \beta $$ three";

preg_match("/[^$]+?[$]{1,2}[^$]+?[$]{1,2}/i", $str, $matches);
// [^$] - matches all symbols excepting '$'
// [$]{1,2} - symbolic class - matches only '$' symbol in quantity from 1 to 2
// ? - supply "ungreedy" matching

var_dump($matches);

// the output:  "one two $\alpha \beta $"