PHP : How to Replace some text from n th line to m th line from file?

Question

I have a file like some.txt having content :

#start-first
Line 1
Line 2
Line 3
#end-first

#start-second
Line 1
Line 2
Line 3
Line 4
#end-second

#start-n
Line 1
Line 2
Line 3
Line 4
...
...
#end-n

I want to delete content from file from #start-second to #end-second or from #start-n to #end-n, actually #start-second is Start Marker for Second Text Block of file and #end-second is End Marker for Second Text Block of file.

How to delete content from Specific Start Block to same End block ?

Answer 1

If these files are really big, there is a fairly lightweight solution:

$file = file_get_contents("example.txt");
// Find the start "#start-$block", "#end-$block" and the length between them:
$start = strpos($file, "#start-$block");
$end = strpos($file, "#end-$block");
$length = $end-$start+strlen("#end-$block");

$file = substr_replace($file, '', $start, length);
file_put_contents("example.txt", $file);

---

My original answer started with a regex:

$block = 4;

// Open the file
$file = openfile("example.txt");

// replace #start-$block, #end-$block, and everything inbetween with ''
$file = preg_replace("/#start\-".$block."(?:.*?)#end\-".$block."/s", '', $file);

// Save the changes
file_put_contents("example.txt", $file);

Regexes are expensive though, but sometimes easier to understand.