How to implement linux commands in php

php method to implement linux commands: 1. Create a PHP sample file; 2. Enter "#!/usr/bin/env php" on the first line; 3. Pass "if(2 != count ($argv)){...}" and other codes can implement the Linux command "tail -f".

The operating environment of this article: linux5.9.8 system, PHP version 7.1, Dell G3 computer.

How does php implement linux commands?

PHP implements linux commandstail -f

Suddenly today Thinking of a question someone asked me before, how to implement the command tail -f in Linux through PHP, let me analyze and implement it here.

This is quite simple when you think about it. It detects the file through a loop to see if the size of the file has changed. If there is a change, output the changed part of the file. Of course, there will be a lot of details in it. Here is a detailed analysis. Down.

If the initial file is too large or the content has been changed too much

At this time, a lot of content is output at once and may not be visible clearly, so I set a threshold here8192, when the content When the length exceeds this threshold, only the last 8192 bytes will be output, so that there will be no problem of unclear visibility due to large area refresh.

How to detect changes in file size

This question is the core of this program. Whether it can succeed or not depends on this part of the performance.
My implementation here is as follows:

• Open the file handle$fp. Please note that the file handle here needs to be opened and closed only once in the whole process. So put it outside the loop.
• Initialize the current file size file_size and file_size_new to 0.
  • Update in the loopfile_size_newFile size, please note here that before getting the file size in php, you must run the function clearstatcache() to clear the file status cache, otherwise get File sizes may vary.
  • Calculate add_size = file_size_new - file_size to see if the file size changes. If so, move the file pointer to the specified position, then output the newly added content and update file_size The value is new_file_size.
  • usleep(50000), sleep for 1/20 seconds.

Code implementation

#!/usr/bin/env php 
<?php if(2 != count($argv)){
    fwrite(
        STDERR,
        "调用格式错误！使用格式 ./tail filename".PHP_EOL
    );  
    return 1;
}

$file_name      = $argv[1];
define("MAX_SHOW", 8192);

$file_size      = 0;
$file_size_new  = 0;
$add_size       = 0;
$ignore_size    = 0;
$fp = fopen($file_name, "r");
while(1){
    clearstatcache();
    $file_size_new  = filesize($file_name);
    $add_size       = $file_size_new - $file_size;
    if($add_size > 0){ 
        if($add_size > MAX_SHOW){
            $ignore_size    = $add_size - MAX_SHOW;
            $add_size       = MAX_SHOW;
            fseek($fp, $file_size + $ignore_size);
        }   
        fwrite(
            STDOUT,
            fread($fp, $add_size)
        );  
        $file_size  = $file_size_new;
    }
    usleep(50000);
}

fclose($fp);

Code implementation#!/usr/bin/env php in the first line here tells the executable Files and executable files php are searched in the system PATH. The advantage of this is that it has good portability.

2016-02-22 11:28:51Improvement

I checked the PHP official manual, the fseek function can be improved here, this function It also accepts a third parameter, indicating the type of offset pointer. The default is SEEK_SET, which is the offset from the beginning. It can also be set to SEEK_CUR, which indicates the offset from the current position, so here Change to fseek($fp, $ignore_size, $ignore_size);

The following are the results

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