Here is a quick snippet to get all user meta data by email address in WordPress. The following code will print all user meta data for given email address in wordpress.

$user = get_user_by( 'email', $email_address );
$user_id=$user->ID;
$all_meta_for_user = get_user_meta( $user_id );
print_r( $all_meta_for_user );

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Here is a quick snippet to get all user meta data by user_id in WordPress. The following code will print all user meta data for particular user.

$all_meta_for_user = get_user_meta( $user_id );
print_r( $all_meta_for_user );

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Here is a quick snippet to check whether the user is exists or not by email_address in WordPress.

if( get_user_by( 'email', $email_address ) == false )
{
    // The user doesn't exist
}
else
{
    // The user exists
}

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Here is a quick snippet to check whether the user is exists or not by user_id in WordPress.

$user = get_userdata( $user_id );
if ( $user === false ) 
{
    // The user doesn't exist
}
else 
{
    // The user exists
}

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Here is a quick snippet to remove woocommerce coupon field from woocommerce checkout page. When you enable the use of coupons, woocommerce adds the apply coupon form in cart and checkout page. For our customization want to remove woocommerce coupon field from checkout page then place the following snippet in functions.php within your theme folder!.

function hide_coupon_field_on_woocommerce_checkout( $enabled ) {
	if ( is_checkout() ) {
		$enabled = false;
	}
	return $enabled;
}
add_filter( 'woocommerce_coupons_enabled', 'hide_coupon_field_on_woocommerce_checkout' );

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Here is a quick snippet to remove woocommerce coupon field from woocommerce cart page. When you enable the use of coupons, woocommerce adds the apply coupon form in cart and checkout page. For our customization want to remove woocommerce coupon field from cart page then place the following snippet in functions.php within your theme folder!.

function hide_coupon_field_on_woocommerce_cart( $enabled ) {
	if ( is_cart() ) {
		$enabled = false;
	}
	return $enabled;
}
add_filter( 'woocommerce_coupons_enabled', 'hide_coupon_field_on_woocommerce_cart' );

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Here is a quick snippet to add new custom currency and symbol to wocommerce. Place the following snippet in functions.php within your theme folder. After adding this code your currency will be available in your WooCommerce settings page.

add_filter( 'woocommerce_currencies', 'add_my_custom_currency' );

function add_my_custom_currency( $currencies ) {
     $currencies['BOO'] = __( 'Your currency name', 'woocommerce' );
     return $currencies;
}

add_filter('woocommerce_currency_symbol', 'add_my_custom_currency_symbol', 10, 2);

function add_my_custom_currency_symbol( $currency_symbol, $currency ) {
     switch( $currency ) {
          case 'BOO': $currency_symbol = '$'; break;
     }
     return $currency_symbol;
}

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Add the following code in functions.php within your theme folder for redirect customers into home page after logout in WordPress

add_filter('logout_url', 'new_logout_url', 10, 2);
function new_logout_url($logouturl, $redir)
{
	$redir = get_option('siteurl');
	return $logouturl . '&redirect_to=' . urlencode($redir);
}

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You can use the following code for add custom CSS in WordPress. add your styles in commented part.

add_action(‘admin_head’, ‘my_study_style’);
function my_study_style()
{
//add your styles here
}

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You can use the function get_the_category_list() for this process.

<?php
$categories = get_the_category();
$separator = ' ';
$output = '';
if($categories){
	foreach($categories as $category) {
		$output .= '<a href="'.get_category_link( $category->term_id ).'" title="' . esc_attr( sprintf( __( "View all posts in %s" ), $category->name ) ) . '">'.$category->cat_name.'</a>'.$separator;
	}
echo trim($output, $separator);
}
?>

For more : http://codex.wordpress.org/Template_Tags/get_the_category