Karakter sayısı sınırlama nasıl yapabilirim?

<meta name="description" content="<?php echo get_post_meta($post->ID, 'desc', true); ?>" />

function be_attachment_field_credit( $form_fields, $post ) {
	$form_fields['description'] = array(
		'label' => 'Description',
		'input' => 'text',
		'value' => get_post_meta( $post->ID, 'desc', true ),
	);

	return $form_fields;

function be_attachment_field_credit_save( $post, $attachment ) {
	if( isset( $attachment['description] ) )
		update_post_meta( $post['ID'], 'desc', $attachment['description'] );
}

	return $post;
}

add_filter( 'attachment_fields_to_save', 'be_attachment_field_credit_save', 10, 2 );

substr($veri,$baslangic,$bitis);

substr($veri,0,100);

substr($veri,$baslangic,$bitis);

substr($veri,0,100);

<meta name="description" content="<?php echo get_post_meta($post->ID, 'anla', true); ?>" />

.

<meta name="description" content="<?php echo substr(get_post_meta($post->ID, 'anla', true),0,100); ?>" />