使用 PHP 从文件中读取最后几行(即“ tail”)的最佳方法是什么？

这也会奏效:

$file = new SplFileObject("/path/to/file");
$file->seek(PHP_INT_MAX); // cheap trick to seek to EoF
$total_lines = $file->key(); // last line number


// output the last twenty lines
$reader = new LimitIterator($file, $total_lines - 20);
foreach ($reader as $line) {
echo $line; // includes newlines
}

或者没有 LimitIterator:

$file = new SplFileObject($filepath);
$file->seek(PHP_INT_MAX);
$total_lines = $file->key();
$file->seek($total_lines - 20);
while (!$file->eof()) {
echo $file->current();
$file->next();
}

不幸的是，您的 testcase 在我的机器上出现了错误，所以我不能告诉您它的性能如何。

这是一个修改过的版本，也可以跳过最后一行:

/**
* Modified version of http://www.geekality.net/2011/05/28/php-tail-tackling-large-files/ and of https://gist.github.com/lorenzos/1711e81a9162320fde20
* @author Kinga the Witch (Trans-dating.com), Torleif Berger, Lorenzo Stanco
* @link http://stackoverflow.com/a/15025877/995958
* @license http://creativecommons.org/licenses/by/3.0/
*/
function tailWithSkip($filepath, $lines = 1, $skip = 0, $adaptive = true)
{
// Open file
$f = @fopen($filepath, "rb");
if (@flock($f, LOCK_SH) === false) return false;
if ($f === false) return false;


if (!$adaptive) $buffer = 4096;
else {
// Sets buffer size, according to the number of lines to retrieve.
// This gives a performance boost when reading a few lines from the file.
$max=max($lines, $skip);
$buffer = ($max < 2 ? 64 : ($max < 10 ? 512 : 4096));
}


// Jump to last character
fseek($f, -1, SEEK_END);


// Read it and adjust line number if necessary
// (Otherwise the result would be wrong if file doesn't end with a blank line)
if (fread($f, 1) == "\n") {
if ($skip > 0) { $skip++; $lines--; }
} else {
$lines--;
}


// Start reading
$output = '';
$chunk = '';
// While we would like more
while (ftell($f) > 0 && $lines >= 0) {
// Figure out how far back we should jump
$seek = min(ftell($f), $buffer);


// Do the jump (backwards, relative to where we are)
fseek($f, -$seek, SEEK_CUR);


// Read a chunk
$chunk = fread($f, $seek);


// Calculate chunk parameters
$count = substr_count($chunk, "\n");
$strlen = mb_strlen($chunk, '8bit');


// Move the file pointer
fseek($f, -$strlen, SEEK_CUR);


if ($skip > 0) { // There are some lines to skip
if ($skip > $count) { $skip -= $count; $chunk=''; } // Chunk contains less new line symbols than
else {
$pos = 0;


while ($skip > 0) {
if ($pos > 0) $offset = $pos - $strlen - 1; // Calculate the offset - NEGATIVE position of last new line symbol
else $offset=0; // First search (without offset)


$pos = strrpos($chunk, "\n", $offset); // Search for last (including offset) new line symbol


if ($pos !== false) $skip--; // Found new line symbol - skip the line
else break; // "else break;" - Protection against infinite loop (just in case)
}
$chunk=substr($chunk, 0, $pos); // Truncated chunk
$count=substr_count($chunk, "\n"); // Count new line symbols in truncated chunk
}
}


if (strlen($chunk) > 0) {
// Add chunk to the output
$output = $chunk . $output;
// Decrease our line counter
$lines -= $count;
}
}


// While we have too many lines
// (Because of buffer size we might have read too many)
while ($lines++ < 0) {
// Find first newline and remove all text before that
$output = substr($output, strpos($output, "\n") + 1);
}


// Close file and return
@flock($f, LOCK_UN);
fclose($f);
return trim($output);
}

还有一个函数，您可以使用正则表达式来分隔项

$last_rows_array = file_get_tail('logfile.log', 100, array(
'regex'     => true,          // use regex
'separator' => '#\n{2,}#',   //  separator: at least two newlines
'typical_item_size' => 200, //   line length
));

功能:

// public domain
function file_get_tail( $file, $requested_num = 100, $args = array() ){
// default arg values
$regex         = true;
$separator     = null;
$typical_item_size = 100; // estimated size
$more_size_mul = 1.01; // +1%
$max_more_size = 4000;
extract( $args );
if( $separator === null )  $separator = $regex ? '#\n+#' : "\n";


if( is_string( $file ))  $f = fopen( $file, 'rb');
else if( is_resource( $file ) && in_array( get_resource_type( $file ), array('file', 'stream'), true ))
$f = $file;
else throw new \Exception( __METHOD__.': file must be either filename or a file or stream resource');


// get file size
fseek( $f, 0, SEEK_END );
$fsize = ftell( $f );
$fpos = $fsize;
$bytes_read = 0;


$all_items = array(); // array of array
$all_item_num = 0;
$remaining_num = $requested_num;
$last_junk = '';


while( true ){
// calc size and position of next chunk to read
$size = $remaining_num * $typical_item_size - strlen( $last_junk );
// reading a bit more can't hurt
$size += (int)min( $size * $more_size_mul, $max_more_size );
if( $size < 1 )  $size = 1;


// set and fix read position
$fpos = $fpos - $size;
if( $fpos < 0 ){
$size -= -$fpos;
$fpos = 0;
}


// read chunk + add junk from prev iteration
fseek( $f, $fpos, SEEK_SET );
$chunk = fread( $f, $size );
if( strlen( $chunk ) !== $size )  throw new \Exception( __METHOD__.": read error?");
$bytes_read += strlen( $chunk );
$chunk .= $last_junk;


// chunk -> items, with at least one element
$items = $regex ? preg_split( $separator, $chunk ) : explode( $separator, $chunk );


// first item is probably cut in half, use it in next iteration ("junk") instead
// also skip very first '' item
if( $fpos > 0 || $items[0] === ''){
$last_junk = $items[0];
unset( $items[0] );
} // … else noop, because this is the last iteration


// ignore last empty item. end( empty [] ) === false
if( end( $items ) === '')  array_pop( $items );


// if we got items, push them
$num = count( $items );
if( $num > 0 ){
$remaining_num -= $num;
// if we read too much, use only needed items
if( $remaining_num < 0 )  $items = array_slice( $items, - $remaining_num );
// don't fix $remaining_num, we will exit anyway


$all_items[] = array_reverse( $items );
$all_item_num += $num;
}


// are we ready?
if( $fpos === 0 || $remaining_num <= 0 )  break;


// calculate a better estimate
if( $all_item_num > 0 )  $typical_item_size = (int)max( 1, round( $bytes_read / $all_item_num ));
}


fclose( $f );


//tr( $all_items );
return call_user_func_array('array_merge', $all_items );
}

我喜欢下面的方法，但它不会工作的文件高达2GB。

<?php
function lastLines($file, $lines) {
$size = filesize($file);
$fd=fopen($file, 'r+');
$pos = $size;
$n=0;
while ( $n < $lines+1 && $pos > 0) {
fseek($fd, $pos);
$a = fread($fd, 1);
if ($a === "\n") {
++$n;
};
$pos--;
}
$ret = array();
for ($i=0; $i<$lines; $i++) {
array_push($ret, fgets($fd));
}
return $ret;
}
print_r(lastLines('hola.php', 4));
?>

我的小复印粘贴解决方案后，在这里阅读所有这一切。

/**
* @param $pathname
* @param $lines
* @param bool $echo
* @return int
*/
private function tailonce($pathname, $lines, $echo = true)
{
$realpath = realpath($pathname);
$fp = fopen($realpath, 'r', FALSE);
$flines = 0;
$a = -1;
while ($flines <= $lines) {
fseek($fp, $a--, SEEK_END);
$char = fread($fp, 1);
if ($char == "\n") $flines++;
}
$out = fread($fp, 1000000);
fclose($fp);
if ($echo) echo $out;
return $a+2;
}

tail -f中的连续尾部函数
它不关闭 $fp 因为你必须杀死它 反正是 Ctrl-C。 ussleep 节省了你的 CPU 时间，目前为止只在 windows 上测试过。

/**
* @param $pathname
*/
private function tail($pathname)
{
$realpath = realpath($pathname);
$fp = fopen($realpath, 'r', FALSE);
$lastline = '';
fseek($fp, $this->tailonce($pathname, 1, false), SEEK_END);
do {
$line = fread($fp, 1000);
if ($line == $lastline) {
usleep(50);
} else {
$lastline = $line;
echo $lastline;
}
} while ($fp);
}

您需要将这些代码放到一个类中！