Drupal 7 - Presave a node (or doing custom validation and/or manipulation on field values)

I now have the simple specification that I have a text field in a Node which always needs to be uppercase, whatever the editor enters in the field. As a second specification I also want all spaces removed from the field values.
I could not find an example snippet to start up from, so I thought better publish this, maybe someone else will have  an easier live than me....

Specification
Field x: user may enter any character, but on saving the field all characters will be uppercased.
Field x: Also, alle whitespaces will be removed from the string


1. Create a module, in this example called customchr.
1. a Create info file  customchr.info

name = Custom CHR
description = Custum manipulations for the CHR site
package = Overboord
core = 7.x


2. Create module file customchr.module

function customchr_node_presave($node) {
  if ($node->type == 'publication') {
    // convert to uppercase
    $tempstring=strtoupper($node->field_publication_code[und][0][value]);
    // strip all whitespaces
    $node->field_publication_code[und][0][value]= preg_replace('/\s+/', '', $tempstring);
  }
}