Question

PHP (among others) will execute the deepest function first, working its way out. For example,

$text = strtoupper(str_replace('_', ' ', file_get_contents('file.txt'))); 

I’m doing something very similar to the above example for a template parser. It looks for the tags

{@tag_name} 

and replaces it with a variable of the name $tag_name. One more example:

$a = 'hello'; $b = ' world'; INPUT = 'This is my test {@a{@b}} string.'; OUTPUT (step 1) = 'This is my test {@a} world string.'; OUTPUT output = 'This is my test hello world string.'; 

How can I go about doing this? Does this make sense? If not, I can try explaining better.

Answer 1

I’m not sure I understand the nesting in your example, as the example doesn’t demonstrate a purpose behind nesting. Your example input could very easily be

'This is my test {@a} {@b} string.' 

And using arrays in str_replace would handle this very simply and quickly.

$aVars = array('{@a}' => 'hello', '{@b}' => 'world'); $sString = 'This is my test {@a} {@b} string.';  echo str_replace(array_keys($aVars), array_values($aVars), $sString); 

Which gives us

This is my test hello world string.

Now, a recursive function for this isn’t too difficult, though I’m not sure I understand how useful it would be. Here’s a working example:

function template($sText, $aVars) {     if (preg_match_all('/({@([^{}]+)})/',                        $sText, $aMatches, PREG_SET_ORDER)) {         foreach($aMatches as $aMatch) {             echo '<pre>' . print_r($aMatches, 1) . '</pre>';              if (array_key_exists($aMatch[2], $aVars)) {                 // replace the guy inside                 $sText = str_replace($aMatch[1], $aVars[$aMatch[2]], $sText);                  // now run through the text again since we have new variables                 $sText = template($sText, $aVars);             }         }     }      return $sText; } 

That print_r will show you what the matches look like so you can follow the function through its paces. Now lets try it out…

$aVars = array('a' => 'hello', 'b' => 'world'); $sStringOne = 'This is my test {@a} {@b} string.'; $sStringTwo = 'This is my test {@a{@b}} string.';  echo template($sStringOne, $aVars) . '<br />'; 

First Result:

This is my test hello world string.

Now lets try String Two

echo template($sStringTwo, $aVars) . '<br />'; 

Second Result:

This is my test {@aworld} string.

That may very well be what you’re looking for. Obviously you would need an aworld variable for this to work recursively…

$aVars = array('a' => '', 'b' => '2', 'a2' => 'hello world');  echo template($sStringTwo, $aVars) . '<br />'; 

And our result.

This is my test hello world string.

And just for some fun with the recursion…

$aVars = array('a3' => 'hello world', 'b2' => '3', 'c1' => '2', 'd' => '1'); $sStringTre = 'This is my test {@a{@b{@c{@d}}}} string.';  echo template($sStringTre, $aVars) . '<br />'; 

This is my test hello world string.

Not sure if this is what you’re asking for…