<?php /* for Magento 2.4 */ $writer = new \Zend_Log_Writer_Stream(BP . '/var/log/custom.log'); $logger = new \Zend_Log(); $logger->addWriter($writer); $logger->info('Text Log'); //Text Log $logger->info('Array Log'.print_r($myArrayVar, true)); // Array Log
?>
<?php $writer = new \Zend\Log\Writer\Stream(BP . '/var/log/logfile.log'); $logger = new \Zend\Log\Logger(); $logger->addWriter($writer); $logger->info('Simple Text Log'); // Simple Text Log $logger->info('Array Log'.print_r($myArrayVar, true)); // Array Log
?> 

Mage::log('message',null,'logfile.log',true);
Mage::log(print_r($arr, 1), null, 'logfile.log',true);

<?php
namespace Mageplaza\HelloWorld\Post;
class Post extends \Magento\Framework\View\Element\Template
{ protected $_logger; public function __construct( \Magento\Backend\Block\Template\Context $context, \Psr\Log\LoggerInterface $logger, array $data = [] ) { $this->_logger = $logger; parent::__construct($context, $data); } public function testLogging() { // monolog's Logger class // MAGENTO_ROOT/vendor/monolog/monolog/src/Monolog/Logger.php // saved in var/log/debug.log $this->_logger->debug('debug1234'); //Output: [2017-02-22 04:48:44] main.DEBUG: debug1234 {"is_exception":false} [] $this->_logger->info('info1234'); // Write to default log file: var/log/system.log //Output: [2017-02-22 04:52:56] main.INFO: info1234 [] [] $this->_logger->alert('alert1234'); // Write to default log file: var/log/system.log //Output: [2017-02-22 04:52:56] main.ALERT: alert1234 [] [] $this->_logger->notice('notice1234'); // Write to default log file: var/log/system.log //Output: [2017-02-22 04:52:56] main.NOTICE: notice1234 [] [] // Write to default log file: var/log/system.log $this->_logger->error('error1234'); //Output: [2017-02-22 04:52:56] main.ERROR: error1234 [] [] // Write to default log file: var/log/system.log $this->_logger->critical('critical1234'); //Output: [2017-02-22 04:52:56] main.CRITICAL: critical1234 [] [] // Adds a log record at an arbitrary level $level = 'DEBUG'; // saved in var/log/debug.log $this->_logger->log($level,'debuglog1234', array('msg'=>'123', 'new' => '456')); //Output: [2017-02-22 04:52:56] main.DEBUG: debuglog1234 {"msg":"123","new":"456","is_exception":false} [] // Write to default log file: var/log/system.log $level = 'ERROR'; $this->_logger->log($level,'errorlog1234', array( array('test1'=>'123', 'test2' => '456'), array('a'=>'b') )); //Output: [2017-02-22 04:52:56] main.ERROR: errorlog1234 [{"test1":"123","test2":"456"},{"a":"b"}] [] }
}
?>