Learn BASH -- Pipelines (from bash manual)

1. Pipe's function: 

    The output of each command in the pipeline is connected via a pipeto the input of the next command. That is, each command reads the previous command's output. Thisconnection is performed before any redirections specified by thecommand.

2. Note: If ‘|&’ is used, the standard error of command1 is connected tocommand2's standard input through the pipe; it is shorthand for2>&1 |. This implicit redirection of the standard error isperformed after any redirections specified by the command.

3. Each command in a pipeline is executed in its own subshell

4.