正则表达式 - 验证结束标签 - 模板引擎

Question

For a particular template engine, where user will add/update templates to send messages to customers.

I am using regular expressions to validate each template literals having double tags, a starting << and closing >> tag in a string.

Given is valid template engine.

Hi <<cName>>, please make your payment of $ <<totAmt>>   
for Account number <<accNum>> given by <<agentName>> at this link <<payLink>>
The validity of this link is 30 minutes.  

Given are valid template literals
<<cName>>
<<totAmt>>
<<accNum>>
<<agentName>>
<<payLink>>

Given are invalid template literals
<<cName>
<<agentName>>>>>>>>
<cName>
<<<<<payLink>>
<<cName<<>>

Currently give is my workaround.

First I get all template literals using given Regex.

<.*?>(?!>)

Then loop through each literals to validate using given Regex in PHP. If any literal is invalid, so given template updated by user is invalid.

^<{2}[^<>]+>{2}(?!>)

$is_tpl_valid = true; //template is valid

$template = 'Hi <<cName>>, please make your payment of $ <<totAmt>>   
for Account number <<accNum>> given by <agentName>> at this link <<payLink>>
The validity of this link is 30 minutes.';

echo '<br/> --- File: ' . __FILE__ . '#'. __LINE__ . '------- $template -> ' . $template . ' --------------<br/>';
if(preg_match_all('#<.*?>(?!>)#', $template, $matched))
{
    echo '<pre>';
    print_r($matched);
    foreach($matched[0] as $item)
    {
        if($is_tpl_valid && !preg_match('#^<{2}[^<>]+>{2}(?!>)#', $item))
        {
            echo '<br/> --- File: ' . __FILE__ . '#'. __LINE__ . '------- $item -> ' .  $item . ' --------------<br/>';
            $is_tpl_valid = false; //template is invalid
        }
    }
}

Can we do it in single Regex or any better solution (in JS / PHP) to find invalid template literals.

Thanks in advance

Answer 1

To validate tags you can try this pattern

(?<!<)<<[^<>]+>>(?!>)

• (?<!<) - Match should not be preceded by <
• << - Match <<
• [^<>]+ - Match anything except <>
• >> - Match >>
• (?!>) - Match should not be followed by >

Regex Demo

Answer 2

Use the verbs (*SKIP)(*FAIL) .

This will attempt to match valid tags then FAIL or match everything with the form <+blah>+ that are, in fact, invalid:

$text = '
<<cName>>
<<totAmt>>
<<accNum>>
<<agentName>>
<<payLink>>

<<cName>
<<agentName>>>>>>>>
<cName>
<<<<<payLink>>
<<cName<<>> 
';

preg_match_all('/(?<!<)<<\w+>>(?!>)(*SKIP)(*FAIL)|<+[\w<]+>+/', $text, $m);
print_r($m);

Output:

Array
(
    [0] => Array
        (
            [0] => <<cName>
            [1] => <<agentName>>>>>>>>
            [2] => <cName>
            [3] => <<<<<payLink>>
            [4] => <<cName<<>>
        )

)