Yes, this is a good approach.

• read a line (and save it into a variable)
• parse the line into fields, e.g. by using split
• calculate value for 'last field' from 2nd field (making sure there actually is a 2nd field) -> usually done by an 'if' with a regexp match condition
• append value to current line, e.g. by using the .= operator

Saving the current line into a variable is useful if you want to keep the current line 'as-is'. If you want to get fancy you could also create an intermediate representation of the output in memory (probably as an 'array of arrays') calculate the longest value length for each column and create properly indented columns from scratch.
Just remember: You can't spell 'pretty pointless' without 'pretty'. ;)