File reading, searching and looping problems - php

Question

So i've been trying to write this little piece of code to read a file (status.txt), search it for 1 of 4 keywords and loop until either time runs out (5 minutes) or it finds one of the words. I've already written a few simple php scripts to write the words to a txt file, but I can't seem to get this part to work. It either doesn't clear the file in the beginning or seems to hang and never picks up the changes. Any advice would be hugely helpful.
<?php
//Variables
$stringG = "green";
$stringR = "red";
$stringB = "blue";
$stringO = "orange";
$clear = "";
$statusFile = "status.txt";
//erase file
$fh = fopen($statusFile, 'w'); //clear the file with "clear"
fwrite($fh, $clear);
fclose($fh);
//Insert LOOP
$counter = 0;
while ( $counter <= 10 ) {
//echo "loop begun";
// Read THE FILE
$fh = fopen($statusFile, 'r');
$data = fread($fh, filesize($statusFile));
fclose($fh);
//process the file
if(stristr($data,$stringG)) {
echo "Green!";
$counter = $counter + 30; //stop if triggered
}
elseif (stristr($data,$stringR)) {
echo "Red";
$counter = $counter + 30; //stop if triggered
}
elseif (stristr($data,$stringB)) {
echo "Blue";
$counter = $counter + 30; //stop if triggered
}
elseif (stristr($data,$stringO)) {
echo "Orange";
$counter = $counter + 30; //stop if triggered
}
else {
//increment loop counter
$counter = $counter + 1;
//Insert pause
sleep(10);
}
}
?>

Answer 1

You should open the file before your read loop, and close it after the loop. As in :
open the file
loop through the lines in the file
close the file
Also, if you clear the file before you read it, isn't it going to be empty every time?

Answer 2

Well, first of all, you don't need to "clear" the file this way... The "w" option in fopen will already do that for you.
Also, I wouldn't try to read the whole file at once, because, if it's very large, that won't work without intense memory usage.
What you should do is read the file sequentially, which means you always read a fixed amount of bytes and look for the keywords. To avoid losing keywords which are cut in half by your reading mechanism, you could make your reads overlay a bit (the length of your longest keyword-1), to solve that problem.
Then you should modify your while loop so that it also checks if you are at the end of the file ( while(!feof($fh)) ).
PS: It has been mentioned that you clear your file before reading it. What I understood is that your file gets a lot of input really fast, so you expect it to already have content again when you reopen it. If that's not the case, you really need to rethink your logic ;)
PPS: You don't need to abort your while loop by incrementing your counter variable past the boundaries you define. You can also use the break-keyword.

Answer 3

You haven't included the code which deletes the file in the while loop, so it only clears the file once. Also, I'd use unlink($statusFile); to delete the file.

Answer 4

You should rather use for cycle. And to your problem - you clear the file, then get the data from it. Try dumping this $data, you'll end up with string(0) "" for sure. First, save the data, then clear the file.
Edit: If you are changing the file in the loop itself in another thread, there's another problem. You should look after anatomic file stream. For example, you can use Nette SafeStream class.