how to create php regex - php

Question

I am trying to create a regex to replace a string. Here is my pattern:
\{mailMerge: details_activity_number\\}
When I do a search like this on a string like this:
hello {mailMerge: details_activity_number\}world
its fine. But, if there's a line break like this:
hello \{
mailMerge: details_activity_number\} world
it breaks. Here is my code in PHP:
$pattern = '\{mailMerge: 'mailMerge: details_activity_number'\}';
$content = str_replace($pattern, $value, $content);
Can anyone help me with creating a pattern that would take into consideration possible line breaks/white spaces/etc to guarantee a match?
thanks
EDIT
private function findAndReplace($content, $mergedArray){
$test=$content;
try{
foreach($mergedArray as $ArrayKey => $ArrayValue){
foreach ($ArrayValue as $key => $value) {
$pattern = "\{\s*mailMerge:\s+". $key ."\s*\\\}";
if($value){
$test = preg_replace($pattern, $value, $test);
}else{
$test = preg_replace($pattern, "No Value Exists", $test);
}
}
}
}catch(Exception $e){
throw $e;
}
return $test;
}

Answer 1

The first version that you posted doesn't allow for any space between { and m. You need to do something like this:
\{\s*mailMerge:\s+details_activity_number\s*\\\}
The \s* means "match zero or more spaces (or other white space, like new lines) here." \s+ means "match one or more spaces (or other white space, like new lines) here."
NOTE: Your code above uses str_replace, but you are trying to do a regex replace. You need to use preg_replace instead of str_replace, like in this code:
$content = "\{mailMerge: 'mailMerge: details_activity_number'\}";
$content = preg_replace('/\{\s*mailMerge:\s+details_activity_number\s*\\\}/m', $value, $content);
EDIT BASED ON COMMENTS: Try this; it is working for me.
$value = "foo barrrrrr";
$content = "hello
{mailMerge: details_activity_number\} world";
$content = preg_replace("/\\\\?\\{\s*mailMerge:\s+details_activity_number\s*\\\\?\\}/m", $value, $content);
echo $content; // produces "hello foo barrrrrr world"