Exercises for cat, head and tail

If we're live, go to https://envs.workroomprds.com/ and pick an environment. Read about these tools at cat, head and tail for Testers

Exercise 1 – exchange experiences

Let's talk: What have we seen cat head and tail used for in testing?

Exercise 2 – demo cat , head and tail to ourselves

Open the terminal, and

1) Try this to pick out all the test definitions in a test file

cat ~/code/rs_py/tests/test_* | grep "def test_"

and consider why you might do this rather than

grep "def test_" ~/code/rs_py/tests/test_*

2) try this to see the tops of all the test files in a directory:

head ~/code/rs_py/tests/test_*

3) Try this to see the access log for the web server – you'll see it change as the page you're working in makes requests of the server.

sudo tail -F /var/log/nginx/access.log

You need sudo to get system access. -F follows the log, updating as it changes.

4) cat will do some transforms – and especially cat -tve will sanitise otherwise unprintable data. Compare head -n 2 /var/log/wtmp and head -n 2 /var/log/wtmp | cat -tve

Exercise 3 – oddities

The stream `/dev/urandom` is full of randomness, so head -c 5 /dev/urandom returns stuff. Try it – then try tail ... . Try cat if you're brave. What's happening here?

Open two terminals, or a terminal and an editor.On the commandline (of a terminal), tail -F whatever.txt. In the other terminal, or in the editor, open whatever.txt , add text, save, check the terminal, repeat. What's happening here?

Just type cat. What's happening here?