Regular expression to extract text between braces

Question

I am trying to extract text between curly braces in PHP. eg

Welcome {$user.first_name} to the {$site} version 1.5. Your username is {$user.username}. Your reputation at present is {$user.reputation.name}

I have used \\{\\$(.*?)\\} which works fine in some cases. This matches:

• {$user.first_name}
• {$site}
• {$user.username}
• {$user.reputation.name}

But now I want to match only text which has single or multiple . (dot) within the braces. ie For the above string I should be able to match only:

• {$user.first_name}
• {$user.username}
• {$user.reputation.name}

Please help me to achieve this! Thanks in Advance.

Answer 1

You can use

\{\$([^.{}]+(?:\.[^.{}]+)+)\}

See regex demo

Note that instead of lazy dot matching .*? , I am using a negated character class [^.{}] that matches any character other than . , { or } . Thus, we match any block that does not contain a . , and is still within the braces.

The regex breakdown:

• \\{\\$ - literal {$
• ([^.{}]+(?:\\.[^.{}]+)+) - Group 1 matching
  • [^.{}]+ - 1 or more characters other than . , { , or }
  • (?:\\.[^.{}]+)+ - 1 or more (due to + ) sequences of
    • \\. - a literal dot
    • [^.{}]+ - 1 or more characters other than . , { , or }
• \\} - literal }

IDEONE demo :

$re = '/\{\$([^.{}]+(?:\.[^.{}]+)+)\}/'; 
$str = "Welcome {\$user.first_name} to the {\$site} version 1.5. Your username is {\$user.username}. Your reputation at present is {\$user.reputation.name}"; 
preg_match_all($re, $str, $matches);
print_r($matches[1]);

Answer 2

you can use this pattern:

~{\$([^}.]*+[^}]+)}~

[^}.]*+ has a possessive quantifier and can't give characters back, so [^}]+ can only match a dot as first character.