Several ways to read large files with PHP

This article mainly introduces several methods of reading large files based on PHP. There are three main methods. Interested friends can refer to it.

Reading large files has always been a headache. If we use PHP to develop and read small files, we can directly use various functions to achieve it. However, once we get to a large article, we will find that the commonly used methods cannot be used normally or It takes too long and gets stuck. Let's take a look at the solution to the problem of reading large files in PHP. I hope the example can help you.

Scenario: PHP reads very large files, such as a 1G log file. I use a 400M access.log file here

1. Use file to read directly

<?php
$starttime=microtime_float();
 
ini_set(&#39;memory_limit&#39;, &#39;-1&#39;);
$file = &#39;testfile.txt&#39;;
 
$data = file($file);
$line = $data[count($data) - 1000];
$endtime=microtime_float();
 
echo count($data),"<br/>";
echo $endtime-$starttime;
 
function microtime_float(){
 list($usec, $sec) = explode(" ", microtime());
 return ((float)$usec + (float)$sec);
}
?>

Run result: 10127784 lines used in total, 7.8764359951s

My computer has 3G memory, this method is not recommended Use, because you need to load all the files into memory

2. Use the linux command tail

<?php
 
$starttime=microtime_float();
 
$file = &#39;testfile.txt&#39;;
$file = escapeshellarg($file); // 对命令行参数进行安全转义
$line = `tail -n 100 $file`;
 
echo $line,"<br/>";
 
$endtime=microtime_float();
echo $endtime-$starttime;
 
function microtime_float(){
 list($usec, $sec) = explode(" ", microtime());
 return ((float)$usec + (float)$sec);
}
 
//end

Running result: only used It can be done easily in a few milliseconds. This method cannot be used under Windows

3. Use the fseek function

This method is the most common method. It does not require reading all the contents of the file. Content, because PHP is written in C, the implementation is similar to reading files in C, through the movement of pointers, so the efficiency is quite efficient. When using fseek to operate files, there are many different methods, and the efficiency may be slightly different.

The following are some commonly used methods

Method 1: Use fopen to open the file (from the file pointer resource handle)

<?php
$starttime=microtime_float();
 
$file = &#39;testfile.txt&#39;;
$fp = fopen($file, "r+");
 
$line = 100;
$pos = -2;
$t =$data="";
 
while ($line > 0)
{
 while ($t != "\n") //换行符
 {
 fseek($fp, $pos, SEEK_END);//移动指针
 $t = fgetc($fp);//获取一个字符
 $pos--;//向前偏移
 }
 
 $t = "";
 $data = fgets($fp);//获取当前行的数据
 $line--;
}
fclose($fp);
echo $data,"<br/>";
$endtime=microtime_float();
 
echo $endtime-$starttime;
 
function microtime_float(){
 list($usec, $sec) = explode(" ", microtime());
 return ((float)$usec + (float)$sec);
}
?>

Running result: 0.338493108749

Method 2: Read piece by piece Get

<?php
$starttime=microtime_float();
 
$file = &#39;testfile.txt&#39;;
$fp = fopen($file, "r");
$num = 10;
$chunk = 4096;//4K的块
$fs = sprintf("%u", filesize($file));
$readData=&#39;&#39;;
$max = (intval($fs) == PHP_INT_MAX) ? PHP_INT_MAX : $fs;
 
for($len = 0; $len < $max; $len += $chunk){
 
 $seekSize = ($max - $len > $chunk) ? $chunk : $max - $len;
 fseek($fp, ($len + $seekSize) * -1, SEEK_END);
 $readData = fread($fp, $seekSize) . $readData;
 
if (substr_count($readData, "\n") >= $num + 1) {
 
 $ns=substr_count($readData, "\n")-$num+2;
 preg_match(&#39;/(.*?\n){&#39;.$ns.&#39;}/&#39;,$readData,$match);
 $data = $match[1];
 break;
}
}
fclose($fp);
echo $data,"<br/>";
 
 
$endtime=microtime_float();
 
echo $endtime-$starttime;
 
function microtime_float(){
 list($usec, $sec) = explode(" ", microtime());
 return ((float)$usec + (float)$sec);
}
?>

Running time: 0.00199198722839

Use fgets function to read line by line

<?php
$file = fopen("testfile.txt","r");
 while(!feof($file))
 {
   echo fgets($file);
 }
 fclose($file);

spl library function

<?php
try{
  foreach( new SplFileObject(&#39;testfile.txt&#39;) as $line)
  echo $line.&#39;<br />&#39;;
}catch (Exception $e){
  echo $e->getMessage();
}

In addition, there are many methods for reading files in blocks on the Internet. Interested readers can try it , I tried without success, it seems that it must contain the newline character "\n".

The above is the entire content of this article, I hope it will be helpful to everyone's study.

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