I have pattern in string to be replaced with something else.
e.g.
$str = '{1} Foo Bar {4}';
I want the above string to be converted like:
$str = arg(0). 'Foo Bar'.arg(4)
Go through this functions
for(i=0;i<n;i++){
$str = str_replace("{i}", arg(i), $str);
}
In such cases it's best to use preg_replace_callback(). It's unclear what arg(4) is, variable or real function call.
Only if you can constrain the matched values, you may use preg_replace with /e like that:
$text = preg_replace('~ [{] (\d+) [}] ~xie', 'arg($1)', $text);
That would invoke arg($decimal) for each occurence of {n}. Workable if you only match decimals like in your example.