Unless you input these strings in this form and output them in the same form and this is the only manipulation you need to do I'd strongly recommend you turn the string into an array where dealing with elements by index is natural.

Perl has powerful ways of manipulating lists including splice, grep, map and array slices. Performing significant array manipulation on a string will make your code hard to read and hard to maintain.

However, in this case it may be that a hash is a better choice. Using 'field' for your variable name implies that the elements have significance related to their original position. By removing elements you mess up that mapping and make it hard to track what is where in the list. Better to name the fields by using a hash then manipulate fields by name. Show us soome of the bigger problem and we can help show you how that goes.