Blocking file-read in php?

Question

I want to read everything from a textfile and echo it. But there might be more lines written to the text-file while I'm reading so I don't want the script to exit when it has reached the end of the file, instead I wan't it to wait forever for more lines. Is this possible in php?

Answer 1

this is just a guess, but try to pass through (passthru) a "tail -f" output.

but you will need to find a way to flush() your buffer.

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IMHO a much nicer solution would be to build a ajax site.

read the contents of the file in to an array. store the number of lines in the session. print the content of the file.

start an ajax request every x seconds to a script which checks the file, if the line count is greater then the session count append the result to the page.

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you could use popen() inststed:

$f = popen("tail -f /where/ever/your/file/is 2>&1", 'r');
while(!feof($f)) {
    $buffer = fgets($f);
    echo "$buffer\n";
    flush();
    sleep(1);
}
pclose($f)

the sleep is important, without it you will have 100% CPU time.

Answer 2

In fact, when you "echo" it, it goes to the buffer. So what you want is "appending" the new content if it's added while the browser is still receiving output. And this is not possible (but there are some approaches to this).

Answer 3

I solved it.

The trick was to use fopen and when eof is reached move the cursor to the previous position and continue reading from there.

<?php
$handle = fopen('text.txt', 'r');
$lastpos = 0;
while(true){
   if (!feof($handle)){
       echo fread($handle,8192);
       flush();
       $lastpos = ftell($handle);
   }else{
       fseek($handle,$lastpos);
   }
}
?>

Still consumes pretty much cpu though, don't know how to solve that.

Answer 4

You may also use filemtime: you get latest modification timestamp, send the output and at the end compare again the stored filemtime with the current one.

Anyway, if you want the script go at the same time that the browser (or client), you should send the output using chunks (fread, flush), then check any changes at the end. If there are any changes, re-open the file and read from the latest position (you can get the position outside of the loop of while(!feof())).