Suppose you had a half dozen HTML files, each with the same footer, e.g.:
This pageset was last updated on (date goes here).
For further information contact:
fred.flintstone@bedrock.gov
Suppose those files were called part_1.html, part_2.html, ..., part_6.html. Each time you made a change to the footer, you'd have to edit all six source files — which could get tedious after a while.
Alternatively, you could include the footer in a single file — say, footer.txt — and have everything but the footer in files called part_1.txt, part_2.txt, ..., part_6.txt.
To change the footer, you'd just edit footer.txt, then do:
cat part_1.txt footer.txt > part_1.html cat part_2.txt footer.txt > part_2.html ... cat part_6.txt footer.txt > part_6.html