Replacing certain parts of certain strings in files

[Archbob]

Lets say I have a large text file and I have a certain string like

block save guard defend

And I want to find this string in the text file(the actual string I'm referring to goes on two lines) and then I want to replace say save with !save if a condition is true but only within this string in the file. There are other places within the file that have 'save' but I don't want to touch them. After replacing save with !save in that string, I want to write the new file over the old file. So how do I do this. Every time I've tried, it replaces every instance of save with !save in the file and not just the instances within the string which is what I want. Note: Actually I just want to replace the last instance. Basically I want to know how to use the limit argument to specify it to only replace the last instance.

[planetsim]

an example

$string = "block save guard defend the save guard";
$string = str_replace("block save guard defend","block !save guard defend",$string);
echo $string;

Should echo out

block !save guard defend the save guard

Hope that helps.

[feldon23]

the actual string I'm referring to goes on two lines

In this case, you would need to search for the EXACT string including that linebreak. So

I just added something to the example:

$linebreak = chr(10).chr(13);
$string = "block save guard defend the save guard"; 
$string = str_replace("block save guard defend".$linebreak."more stuff to match","block !save guard defend".$linebreak."more stuff to match",$string); 
echo $string;