Question

I’m learning sed and i typed this command into cmd prompt of xp.

# echo "All day and all night" | sed 's/day/night/'.

What does | do?

And, I’m getting this weird error if I type this command into
c:\wamp\www\work\delete\test. The command keeps repeating forever.
But If I go one level up or wherever, then it executes once.

Answer 1

| is called a pipe and its effect is to send the output of the first command to the second command.

Here is an interesting reading about it for you, and another one from microsoft