How can I do many things in a single loop?

The loops you have seen so far all have a single command or pipeline in their body, but a loop can contain any number of commands. To tell the shell where one ends and the next begins, you must separate them with semi-colons:

for f in seasonal/*.csv; do echo $f; head -n 2 $f | tail -n 1; done

seasonal/autumn.csv
2017-01-05,canine
seasonal/spring.csv
2017-01-25,wisdom
seasonal/summer.csv
2017-01-11,canine
seasonal/winter.csv
2017-01-03,bicuspid

---

Suppose you forget the semi-colon between the echo and head commands in the previous loop, so that you ask the shell to run:

for f in seasonal/*.csv; do echo $f head -n 2 $f | tail -n 1; done

What will the shell do?