我怎样才能获得这个preg_replace替换？

Question

I'm trying to get a string with #hashtags and convert them into array keys! For example:

string = "hello #world";

I want to replace to "hello $line['world']";

I did this:

$query = mysql_query($sql);
while($line = mysql_fetch_assoc($query)) {
    $code = preg_replace("/(#(\w+))/", $line['$1'], $string);
    echo $code;
}

But I get this warning: "Undefined index: $1" and obviously the echo prints only "hello "

But if I put a valid $line key directly it show its content. Like this:

$query = mysql_query($sql);
while($line = mysql_fetch_assoc($query)) {
    $code = preg_replace("/(#(\w+))/", $line[name], $string);
    echo $code;
}

It shows me "hello nameFromDatabase" for each line of database...

How can I set this $line[XXX] on the preg_replace to get the name located at the #hashtag replacement?

Answer 1

You can't with preg_replace. When you call that function you pass in two arguments:

1. "/(#(\w+))/"
2. $line['$1']

By the time preg is doing the replacement, it's already too late. The second argument has been evaluated and the preg_method cannot go back and re-evaulate the argument to what you want.

preg_replace_callback can do what you want though:

while($line = mysql_fetch_assoc($query)) {
    $code = preg_replace_callback(
       "/(#(\w+))/",
       function($matches) use ($line) {
          return $line[$matches[1]];
       },
       $string
    );
    echo $code;
}