get specific text from .txt file in php - php

Question

I am having a log file like this :
2013-04-08-03-17-52: Cleaning Up all data for restart operation
2013-04-08-03-18-02: Creating new instance of app before closing
2013-04-08-03-18-03: New instance created and running
2013-04-08-03-18-03: Application started
Currently, i am loading full log file every second to show it to the user using jquery ajax, As this being soo inefficient i am trying to figure out some way to load only the updated lines from log file.
Is their any way to get lines only after a particular time stamp 2013-04-08-03-18-03
, For this i will be managing a variable with last timestamp and will be updating it every time i get new lines.
I am kind of New to Php and know only the basics of reading and writing files.

Answer 1

You might want to check the file modification time first to see whether or not you need to reload the log file. You can use the filemtime-function for that.
Furthermore, you can use the file_get_contents-function using an offset to read the file from a certain point.
Edit: So, how does it work?
Suppose you have stored the last modification time in a session variable $_SESSION['log_lastmod'] and the most recent offset in $_SESSION['log_offset'].
session_start();
// First, check if the variables exist. If not, create them so that the entire log is read.
if (!isset($_SESSION['log_lastmod']) && !isset($_SESSION['log_offset'])) {
$_SESSION['log_lastmod'] = 0;
$_SESSION['log_offset'] = 0;
}
if (filemtime('log.txt') > $_SESSION['log_lastmod']) {
// read file from offset
$newcontent = file_get_contents('log.txt', NULL, NULL, $_SESSION['log_offset']);
// set new offset (add newly read characters to last offset)
$_SESSION['log_offset'] += strlen($newcontent);
// set new lastmod-time
$_SESSION['log_lastmod'] = filemtime('log.txt');
// manipulate $newcontent here to what you want it to show
} else {
// put whatever should be returned to the client if there are no updates here
}

Answer 2

You can try
session_start();
if (! isset($_SESSION['log'])) {
$log = new stdClass();
$log->timestamp = "2013-04-08-03-18-03";
$log->position = 0;
$log->max = 2;
$_SESSION['log'] = &$log;
} else {
$log = &$_SESSION['log'];
}
$format = "Y-m-d-:g:i:s";
$filename = "log.txt";
// Get last date
$dateLast = DateTime::createFromFormat($format, $log->timestamp);
$fp = fopen($filename, "r");
fseek($fp, $log->position); // prevent loading all file to memory
$output = array();
$i = 0;
while ( $i < $log->max && ! feof($fp) ) {
$content = fgets($fp);
// Check if date is current
if (DateTime::createFromFormat($format, $log->timestamp) < $dateLast)
continue;
$log->position = ftell($fp); // save current position
$log->timestamp = strstr($content, ":", true); // save curren time;
$output[] = $content;
$i ++;
}
fclose($fp);
echo json_encode($output); // send to ajax

Answer 3

Try something like this:
<?php
session_start();
$lines = file(/*Insert logfile path here*/);
if(isset($_SESSION["last_date_stamp"])){
$new_lines = array();
foreach($lines as $line){
// If the date stamp is newer than the session variable, add it to $new_lines
}
$returnLines = array_reverse($newLines); // the reverse is to put the lines in the right order
} else {
$returnLines = $lines;
}
$_SESSION['last_date_stamp'] = /* Insert the most recent date stamp here */;
// return the $returnLines variable
?>
What this does is reads a file line by line and, if a session variable already exists, add all of the lines where the date stamp is newer than the one in the session variable to a return variable $returnLines, if no session variable exists it will put all of the lines in the file in $returnLines.
After this, it create.updates the session variable for use the next time the code is executed. Finally it returns the log file data by using the $returnLines variable.
Hope this helps.