$data = file("file.txt"); // puts whole file into array
$file = file("file.txt", "w"); // We'll overwrite
foreach($data as $value) { //loop through each line
str_replace("sucks::", "love::", $value); // or "" instead of love :)
fputs($file, $value); // write into the file
}
fclose($file);

<PHP
$newcontent = ""; //Just setting a variable
$file = ("yourfile.txt"); //This is your file
$opened = fopen($file, "r"); //This is where we open the file to read from it
$filecontent = fread($opened, filesize($file)); //Now, we're reading the file
close($opened); //And closing
$filecontent = explode("::", $filecontent); //Now the exploding of the variable
foreach($filecontent => $value){ //A loop that will run once for each piece of the array (I'm not really sure of this syntax
if($value != "sucks"){ //If the piece is NOT "sucks", we continue
$newcontent = $newcontent.$value."::"; //Adding the piece + "::" to a variable
}
}
$opened = fopen($file, "w"); //Now open the file again to write
fwrite($opened, $newcontent); //Put the data in the file
close($opened); //Close the file and we're done
?>