PHP从文件中读取最后几行的最佳方法是什么? [英] What is the best way in PHP to read last lines from a file?

问题描述

在我的PHP应用程序中，我需要从结尾处读取多行 许多文件(主要是日志).有时我只需要最后一个，有时我需要 数十或数百.基本上，我想要像Unix tail一样灵活的东西. 命令.

In my PHP application I need to read multiple lines starting from the end of many files (mostly logs). Sometimes I need only the last one, sometimes I need tens or hundreds. Basically, I want something as flexible as the Unix tail command.

这里存在一些有关如何从文件中获取最后一行的问题(但 我需要 N 行)，并给出了不同的解决方案.我不确定哪个 一个是最好的，并且表现更好.

There are questions here about how to get the single last line from a file (but I need N lines), and different solutions were given. I'm not sure about which one is the best and which performs better.

推荐答案

方法概述

在互联网上搜索时，我遇到了不同的解决方案.我可以将它们分组 三种方法:

Methods overview

Searching on the internet, I came across different solutions. I can group them in three approaches:

使用file() PHP函数的
• 天真用户；
在系统上运行tail命令的
• 作弊程序；
• 全能使用fseek()高兴地在打开的文件中跳转.

• naive ones that use file() PHP function;
• cheating ones that runs tail command on the system;
• mighty ones that happily jump around an opened file using fseek().

我最终选择了(或写出了)五个解决方案，一个天真一个，一个作弊一个 和三个强大的.

I ended up choosing (or writing) five solutions, a naive one, a cheating one and three mighty ones.

1. 最简洁的 天真解决方案 ， 使用内置的数组函数.
2. 仅基于tail 命令的可能解决方案， 有点大问题:如果tail不可用，则它不会运行，即 非Unix(Windows)或在不允许系统的受限环境中 功能.
3. 从文件搜索的末尾读取单个字节的解决方案 (并计数)换行符，请 此处 .
4. 针对大型文件进行了优化的多字节缓冲解决方案 此处
5. 略微解决方案#4的修改版本 ，其中缓冲区长度为 动态，根据要检索的行数决定.

1. The most concise naive solution, using built-in array functions.
2. The only possible solution based on tail command, which has a little big problem: it does not run if tail is not available, i.e. on non-Unix (Windows) or on restricted environments that don't allow system functions.
3. The solution in which single bytes are read from the end of file searching for (and counting) new-line characters, found here.
4. The multi-byte buffered solution optimized for large files, found here.
5. A slightly modified version of solution #4 in which buffer length is dynamic, decided according to the number of lines to retrieve.

所有解决方案有效.从某种意义上说，他们从 我们要求的任何文件和任何数量的行(解决方案#1除外， 如果文件较大，则打破PHP内存限制，不返回任何内容).但是哪一个 更好吗?

All solutions work. In the sense that they return the expected result from any file and for any number of lines we ask for (except for solution #1, that can break PHP memory limits in case of large files, returning nothing). But which one is better?

要回答我运行测试的问题.这些事情就是这样完成的，不是吗?

To answer the question I run tests. That's how these thing are done, isn't it?

我准备了一个示例 100 KB文件，将位于 我的/var/log目录.然后，我编写了一个PHP脚本，该脚本使用 检索 1、2，..，10、20，... 100、200，...，1000 行的五个解决方案 从文件末尾开始.每个测试重复十次(即 类似于 5×28×10 = 1400 测试)，测量经过的平均值 时间(以微秒为单位).

I prepared a sample 100 KB file joining together different files found in my /var/log directory. Then I wrote a PHP script that uses each one of the five solutions to retrieve 1, 2, .., 10, 20, ... 100, 200, ..., 1000 lines from the end of the file. Each single test is repeated ten times (that's something like 5 × 28 × 10 = 1400 tests), measuring average elapsed time in microseconds.

我在本地开发计算机(Xubuntu 12.04， 使用PHP命令行的PHP 5.3.10、2.70 GHz双核CPU，2 GB RAM) 口译员.结果如下:

I run the script on my local development machine (Xubuntu 12.04, PHP 5.3.10, 2.70 GHz dual core CPU, 2 GB RAM) using the PHP command line interpreter. Here are the results:

解决方案#1和#2似乎更糟.解决方案3只有在需要时才是好方法 读几行. 解决方案#4和#5似乎是最好的. 注意动态缓冲区大小如何优化算法:执行时间很短 由于减少了缓冲区，因此几行较小.

Solution #1 and #2 seem to be the worse ones. Solution #3 is good only when we need to read a few lines. Solutions #4 and #5 seem to be the best ones. Note how dynamic buffer size can optimize the algorithm: execution time is a little smaller for few lines, because of the reduced buffer.

让我们尝试使用更大的文件.如果我们必须读取 10 MB 日志文件怎么办?

Let's try with a bigger file. What if we have to read a 10 MB log file?

现在，解决方案1更为糟糕:实际上，加载整个10 MB文件 记入内存并不是一个好主意.我也在1MB和100MB的文件上运行测试， 几乎是相同的情况.

Now solution #1 is by far the worse one: in fact, loading the whole 10 MB file into memory is not a great idea. I run the tests also on 1MB and 100MB file, and it's practically the same situation.

还有小的日志文件?这是 10 KB 文件的图形:

And for tiny log files? That's the graph for a 10 KB file:

解决方案#1是目前最好的解决方案！将10 KB加载到内存中没什么大不了的 对于PHP. #4和#5的表现也不错.但是，这是一个极端情况:10 KB日志 表示大约150/200行...

Solution #1 is the best one now! Loading a 10 KB into memory isn't a big deal for PHP. Also #4 and #5 performs good. However this is an edge case: a 10 KB log means something like 150/200 lines...

您可以下载我所有的测试文件，来源和结果 此处.

You can download all my test files, sources and results here.

最终想法

强烈建议

解决方案#5 :有效伟大的 每个文件都有大小，读取几行时效果特别好.

Final thoughts

Solution #5 is heavily recommended for the general use case: works great with every file size and performs particularly good when reading a few lines.

避免 解决方案#1 应该读取大于10 KB的文件.

Avoid solution #1 if you should read files bigger than 10 KB.

解决方案 #2 和 #3 并不是我进行的每个测试的最佳选择:#2的运行时间不得少于 2ms，而#3受数量的影响很大 您要求的行数(仅使用1或2行就可以了.)

Solution #2 and #3 aren't the best ones for each test I run: #2 never runs in less than 2ms, and #3 is heavily influenced by the number of lines you ask (works quite good only with 1 or 2 lines).

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