How can I use error_log() with WordPress?

Question

I'm trying to use error_log() in a custom WordPress plugin I am building but for some reason, I can't.

When I use error_log() my site just breaks, but I'm not seeing any errors in debug.log.

I have setup debugging in my wp_config.php file like this:

define('WP_DEBUG', true); define('WP_DEBUG_LOG', true); 

Stranegly, if I use error_log() in my theme, the site doesn't break, but nothing is output to debug.log either.

What do I need to do to be able to use error_log() in my WordPress plugin and theme?

I'm using WordPress 3.9.1.

Answer 1

Update 2019

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Enable Debugging

You can simply enable debugging by adding the following code to your wp-config.php:

define( 'WP_DEBUG', true ); define( 'WP_DEBUG_LOG', true ); 

There will be a debug.log file generated in your wp-content folder.

Usage in production environment

If you want to log the errors without printing them in the frontend, add the following line:

define( 'WP_DEBUG_DISPLAY', false ); 

This is really useful in production environments, since the page visitor will not be able to see your logs.

Printing errors

Now you can just write to your log by using the error_log function:

error_log( 'Hello World!' ); 

Or pretty print your output by making use of the print_r method:

error_log( print_r( 'Hello World!', true ) ); 

Pro Tip: If you're using the bash you can observe the log with tail -f wp-content/debug.log