PHP keep me from eval ;) Variables inside string

Question

For reasons I'd rather not get into right now, I have a string like so:

<div>$title</div>

that gets stored in a database using mysql_real_escape_string.

During normal script execution, that string gets parsed and stored in a variable $string and then gets sent to a function($string).

In this function, I am trying to:

function test($string){
  $title = 'please print';
  echo $string;
}
//I want the outcome to be <div>please print</div>

This seems like the silliest thing, but for the life of me, I cannot get it to "interpret" the variables.

I've also tried,

echo html_entity_decode($string);
echo bin2hex(html_entity_decode($string)); //Just to see what php was actually seeing I thought maybe the $ had a slash on it or something.

I decided to post on here when my mind kept drifting to using EVAL().

This is just pseudocode, of course. What is the best way to approach this?

mario · Accepted Answer · 2011-05-03 13:03:02Z

3

Your example is a bit abstract. But it seems like you could do pretty much what the template engines do for these case:

function test($string){
   $title = 'please print';

   $vars = get_defined_vars();
   $string = preg_replace('/[$](\w{3,20})/e', '$vars["$1"]', $string);

   echo $string;
}

Now actually, /e is pretty much the same as using eval. But at least this only replaces actual variable names. Could be made a bit more sophisticated still.

answered May 3, 2011 at 13:03

mario

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Comments

Frank · Accepted Answer · 2011-05-03 12:53:15Z

1

I don't think there is a way to get that to work. You are trying something like this:

$var = "cute text";
echo 'this is $var';

The single quotes are preventing the interpreter from looking for variables in the string. And it is the same, when you echo a string variable.

The solution will be a simple str_replace.

echo str_replace('$title', $title, $string);

But in this case I really suggest Template variables that are unique in your text.

answered May 3, 2011 at 12:53

Frank

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4 Comments

Tanner Ottinger Over a year ago

Smarty uses curly braces around a PHP style var, {$like} {$these}.

Scoobler Over a year ago

Just to note if you change your single apostrophe to a double apostrophe your first example will work, this also goes for setting the string variable, so its not necessarily when you echo a string variable. If you set $string = 'this is $var'; you will get exactly that on echo, but use $string = "this is $var"; you will get this is cute text when echoing $string.

Frank Over a year ago

@Scoobler You are right. The snippet I posted was just intended to demonstrate what happens in the questions example.

Frank Over a year ago

You're welcome! Please note that @markus's answer is more common for single replacements. My method is mainly used for templates where several variables exist in one template string.

markus · Accepted Answer · 2011-05-03 13:02:05Z

1

You just don't do that, a variable is a living thing, it's against its nature to store it like that, flat and dead in a string in the database.

If you want to replace some parts of a string with the content of a variable, use sprintf().

Example

$stringFromTheDb = '<div>%s is not %s</div>';

Then use it with:

$finalString = sprintf($stringFromTheDb, 'this', 'that');

echo $finalString;

will result in:

<div>this is not that</div>

answered May 3, 2011 at 13:02

markus

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1 Comment

Frank Over a year ago

How could i forget about this? Well both answers (mine and this one) have use cases but in general I prefer this. +1

gen_Eric · Accepted Answer · 2011-05-03 13:17:26Z

1

If you know that the variable inside the div is $title, you can str_replace it.

function test($string){
  $title = 'please print';
  echo str_replace('$title', $title, $string);
}

If you don't know the variables in the string, you can use a regex to get them (I used the regex from the PHP manual).

function test($string){
  $title = 'please print';
  $vars = '/(?<=\$)[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*/';
  preg_match_all($vars, $string, $replace);
  foreach($replace[0] as $r){
    $string = str_replace('$'.$r, $$r, $string);
  }
  echo $string;
}

answered May 3, 2011 at 13:17

gen_Eric

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