Shell Programming and Scripting

How can you efficiently add pairs of files together and then paste those pairs,

I have a climate computer at work which spits out temperatures and stuff out twice a day, one for the day-data and one for the night (basically). Every week I want to make a nice overview

The text files are something like this "[date] day.txt" and "[date] night.txt" x7
How would I nicely do this in one bashline?
so:
$cat 2010-08-30\ day.txt 2010-08-30\ night.txt
gives me one day, now paste for a whole week. Can this be done without for loops and such? I really have the feeling I'm overlooking a very simple solution here.

without loop, why?

Code:

find . -type -name "*day.txt" |while read LINE
do
  D=$(echo $line|awk '{print $1}')
  cat "$file" "$D night.txt" > $D.txt
done

With that, you can get one day txt file.

Not sure how to merge these files by weekly, Others maybe can help you.