In PHP, the quickest way to read a file is to use functions such as file, file_get_contents, and just a few lines of code to do what we need. But when the file being manipulated is a large file, these functions may be out of the way, the following will start from a requirement to illustrate the common method of operation when reading large files.
Demand
There is a 800M log file, approximately more than 5 million lines, with PHP returning the last few lines of content.
Implementation method
1. Use the file function directly to manipulate
Note: Because the file function reads everything into memory at once, and PHP prevents some poorly written programs from taking up too much memory and causing the server to go down, the limit is limited to 16M of memory by default, which is through php.ini Memory_ Limit = 16M To set, this value if set-1, the memory makes the usage unrestricted.
The following is a piece of code that uses file to remove the last line of the document.
The entire code execution takes time 116.9613 (s).
Copy CodeThe code is as follows:
$fp = fopen ($file, "R");
$num = 10;
$chunk = 4096;
$fs = sprintf ("%u", FileSize ($file));
$max = (Intval ($fs) = = Php_int_max)? Php_int_max:filesize ($file);
for ($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) {
Preg_match ("!". *?\n) {". ( $num). "} $! ", $readData, $match);
$data = $match [0];
Break
}
}
Fclose ($FP);
Echo $data;
My machine is 2 g of memory, when the press F5 run, the system directly gray, almost 20 minutes after the recovery, it can be seen so large files directly into memory, the consequences is how much serious, so not million can not, memory_limit this thing can not be adjusted too high, otherwise only call room, Let the reset machine out.
2. Directly call the Linux Tail command to display the last few lines
Under the Linux command line, you can directly use Tail-n access.log very easy to display the last few lines of the log file, you can directly use PHP to invoke the tail command, execute PHP code as follows.
Complete code Execution time 0.0034 (s)
Copy CodeThe code is as follows:
File = ' Access.log ';
$file = Escapeshellarg ($file); To safely escape command-line arguments
$line = ' tail-n 1 $file ';
Echo $line;
3. Use PHP fseek directly for file operation
This approach is the most common way, it does not need to read all the contents of the contents of the file, but directly through the pointer to operate, so efficiency is quite efficient. When using fseek to manipulate files, there are many different methods, the efficiency may also be slightly difference, the following are the two commonly used methods.
Method One
First, find the last EOF of the file by fseek, then find the beginning of the last line, take this row of data, then find the starting position of the next line, then take the position of this line, and so on, until the $num line is found.
The implementation code is as follows
Complete code Execution time 0.0095 (s)
Copy CodeThe code is as follows:
function tail ($fp, $n, $base =5)
{
ASSERT ($n >0);
$pos = $n +1;
$lines = Array ();
while (count ($lines) < = $n) {
try{
Fseek ($FP,-$pos, seek_end);
} catch (Exception $e) {
Fseek (0);
Break
}
$pos *= $base;
while (!feof ($fp)) {
Array_unshift ($lines, Fgets ($fp));
}
}
Return Array_slice ($lines, 0, $n);
}
Var_dump (Tail (fopen ("Access.log", "r+"), 10));
Method Two
Or use fseek way from the end of the file to read, but this is not a single read, but a piece of reading, each read a piece of data, the data will be read in a buf, and then by the number of newline characters (\ n) to determine whether the last $num line of data is read.
The implementation code is as follows
The entire code execution takes time 0.0009 (s).
Copy CodeThe code is as follows:
$fp = fopen ($file, "R");
$line = 10;
$pos =-2;
$t = "";
$data = "";
while ($line > 0) {
while ($t! = "\ n") {
Fseek ($fp, $pos, seek_end);
$t = fgetc ($FP);
$pos--;
}
$t = "";
$data. = Fgets ($FP);
$line--;
}
Fclose ($FP);
Echo $data
Method Three
Complete code Execution time 0.0003 (s)
Copy CodeThe code is as follows:
Ini_set (' Memory_limit ', '-1 ');
$file = ' Access.log ';
$data = file ($file);
$line = $data [Count ($data)-1];
Echo $line;
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