Add a "view debug log" link in the WP admin bar

admin-bar-debug-display.php

<?php
/**
 * If we requested the log file, grabit and spit it out.
 *
 * @return HTML
 */
function rkv_adminbar_display_debug_log() {
	
	// Bail without the query string or not on admin.
	if ( ! is_admin() ||  empty( $_GET['viewlog'] ) ) {
		return;
	}
	
	// Set my empty.
	$build  = '';
	
	// Add some basic CSS.
	$build .= '<style>
	p.returnlink { text-align: center; font-size: 14px; line-height: 22px; }
	p.nofile { text-align: center; font-size: 14px; line-height: 22px; font-style: italic; }
	p.codeblock { background-color: #fff; color: #000; font-size: 14px; line-height: 22px; padding: 5px 15px; }
	p.codeblock br { height: 5px; display: block; margin: 0; padding: 0; }
	p strong { font-weight: bold; }	p em { font-style: italic; }
	code, pre { white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word; }
	code pre, span.prewrap { color: #ff0000; }
	</style>';
	
	// Include a "back to admin" link.
	$build .= '<p class="returnlink"><a href="' . admin_url( '/' ) . '">Back To Admin Dashboard</a></p>';
	
	// Check to make sure we have a file.
	if ( ! file_exists( WP_CONTENT_DIR . '/debug.log' ) ) {
		$build .= '<p class="nofile">No debug file exists</p>';
	} else {
		
		// Get my debug file.
		$file   = content_url( '/debug.log' );
		
		// Parse out the data.
		$data   = file_get_contents( $file );
		
		// Trim and break it up.
		$data   = nl2br( trim( $data ) );
		
		// Convert my line breaks.
		$data   = str_replace( array( '<pre>', '</pre>' ), array( '<span class="prewrap">', '</span>' ), $data );
		
		// Generate the actual output.
		$build .= '<p class="codeblock"><code>' . $data . '</code></p>';
	}
	
	// Echo out the build.
	echo $build;
	
	// And die.
	die();
}

add_action( 'admin_init', 'rkv_adminbar_display_debug_log' );

/**
 * Add the link for the debug log file.
 *
 * @param  WP_Admin_Bar $wp_admin_bar  The global WP_Admin_Bar object.
 *
 * @return void.
 */
function rkv_adminbar_link_debug_log( WP_Admin_Bar $wp_admin_bar ) {
	
	// Bail if current user doesnt have cap.
	if ( ! current_user_can( 'manage_options' ) ) {
		return;
	}
	
	// Add the "view debug log" link.
	$wp_admin_bar->add_node(
		array(
			'id'        => 'view-debug-log',
			'title'     => 'Debug Log',
			'href'      => admin_url( '?viewlog=1' ),
			'meta'      => array(
				'title' => 'Debug Log',
				'target' => '_blank',
			),
		)
	);
}

add_action( 'admin_bar_menu', 'rkv_adminbar_link_debug_log', 9999 );