How can I get this preg_replace replacement? - php

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:
"/(#(\w+))/"
$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;
}