split-nagios-log.php

#!/usr/bin/php
<?php

$today = new DateTime();
$firstEntry = new DateTime();
// Set from timestamp (this should be the first log entry of nagios.log.old) 
$firstEntry->setTimestamp( 1555408368 );

$interval = DateInterval::createFromDateString('1 day');
$period = new DatePeriod( $firstEntry, $interval, $today );

$lines = largeFileToDateArray('./nagios.log.old');

foreach( $period as $end ){
	$linesToWrite = [];
	$fileToWrite = "./archives/nagios-" . $end->format("m-d-Y") . "-00.log";
	foreach( $lines as $timestamp => $text ) {
		$lineTimestamp = new DateTime();
		$lineTimestamp->setTimestamp( (int) $timestamp );
		if ( $lineTimestamp->format("m-d-Y") == $end->format("m-d-Y") ) {
			$linesToWrite[] = "[$timestamp] $text";
		}
	}
	file_put_contents( $fileToWrite, implode(PHP_EOL, $linesToWrite) );

}

function largeFileToDateArray( $fileName ) {
	$handle = fopen( $fileName, "r") or die ("Error opening {$fileName}");
	$result = [];
	if ( $handle ) {
		while( !feof( $handle ) ) {
			preg_match('/\[(\d+)\] (.*)/', fgets( $handle ), $groups );
			@$result[ $groups[1] ] = $groups[2];
		}
		fclose( $handle );
	}
	return $result;
}