How to read only 5 last line of the text file in PHP?

Question

I have a file named file.txt which is update by adding lines to it.

I am reading it by this code:

$fp = fopen("file.txt", "r"); $data = ""; while(!feof($fp)) { $data .= fgets($fp, 4096); } echo $data; 

and a huge number of lines appears. I just want to echo the last 5 lines of the file

How can I do that ?

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The file.txt is like this:

11111111111111 22222222222  33333333333333 44444444444  55555555555555 66666666666 

Answer 1

For a large file, reading all the lines into an array with file() is a bit wasteful. Here's how you could read the file and maintain a buffer of the last 5 lines:

$lines=array(); $fp = fopen("file.txt", "r"); while(!feof($fp)) {    $line = fgets($fp, 4096);    array_push($lines, $line);    if (count($lines)>5)        array_shift($lines); } fclose($fp); 

You could optimize this a bit more with some heuristics about likely line length by seeking to a position, say, approx 10 lines from the end, and going further back if that doesn't yield 5 lines. Here's a simple implementation which demonstrates that:

//how many lines? $linecount=5;  //what's a typical line length? $length=40;  //which file? $file="test.txt";  //we double the offset factor on each iteration //if our first guess at the file offset doesn't //yield $linecount lines $offset_factor=1;   $bytes=filesize($file);  $fp = fopen($file, "r") or die("Can't open $file");   $complete=false; while (!$complete) {     //seek to a position close to end of file     $offset = $linecount * $length * $offset_factor;     fseek($fp, -$offset, SEEK_END);       //we might seek mid-line, so read partial line     //if our offset means we're reading the whole file,      //we don't skip...     if ($offset<$bytes)         fgets($fp);      //read all following lines, store last x     $lines=array();     while(!feof($fp))     {         $line = fgets($fp);         array_push($lines, $line);         if (count($lines)>$linecount)         {             array_shift($lines);             $complete=true;         }     }      //if we read the whole file, we're done, even if we     //don't have enough lines     if ($offset>=$bytes)         $complete=true;     else         $offset_factor*=2; //otherwise let's seek even further back  } fclose($fp);  var_dump($lines);