if ($file = fopen("file.txt", "r")) {
    while(!feof($file)) {
        $line = fgets($file);
        # do same stuff with the $line
    }
    fclose($file);
}

SplFileObject在处理大文件时很有用。

function parse_file($filename)
{
    try {
        $file = new SplFileObject($filename);
    } catch (LogicException $exception) {
        die('SplFileObject : '.$exception->getMessage());
    }
    while ($file->valid()) {
        $line = $file->fgets();
        //do something with $line
    }

    //don't forget to free the file handle.
    $file = null;
}

使用缓冲技术读取文件。

$filename = "test.txt";
$source_file = fopen( $filename, "r" ) or die("Couldn't open $filename");
while (!feof($source_file)) {
    $buffer = fread($source_file, 4096);  // use a buffer of 4KB
    $buffer = str_replace($old,$new,$buffer);
    ///
}

你可以为文件使用一个面向对象的接口类——SplFileObject http://php.net/manual/en/splfileobject.fgets.php (PHP 5 >= 5.1.0)

<?php

$file = new SplFileObject("file.txt");

// Loop until we reach the end of the file.
while (!$file->eof()) {
    // Echo one line from the file.
    echo $file->fgets();
}

// Unset the file to call __destruct(), closing the file handle.
$file = null;

这就是我如何处理非常大的文件(测试高达100G)。它比fgets()快

$block =1024*1024;//1MB or counld be any higher than HDD block_size*2
if ($fh = fopen("file.txt", "r")) { 
    $left='';
    while (!feof($fh)) {// read the file
       $temp = fread($fh, $block);  
       $fgetslines = explode("\n",$temp);
       $fgetslines[0]=$left.$fgetslines[0];
       if(!feof($fh) )$left = array_pop($lines);           
       foreach ($fgetslines as $k => $line) {
           //do smth with $line
        }
     }
}
fclose($fh);

如果你想在打开一个大文件时使用foreach而不是while，你可能想在Generator中封装while循环，以避免将整个文件加载到内存中:

/**
 * @return Generator
 */
$fileData = function() {
    $file = fopen(__DIR__ . '/file.txt', 'r');

    if (!$file) {
        return; // die() is a bad practice, better to use return
    }    
    while (($line = fgets($file)) !== false) {
        yield $line;
    }

    fclose($file);
};

像这样使用它:

foreach ($fileData() as $line) {
    // $line contains current line
}

通过这种方式，您可以在foreach()中处理单个文件行。

注意:生成器需要>= PHP 5.5