Dumb question on (Unix) pipe

Question

I'm a Unix newbie - you can tell this as I'm still experimenting with 'cd' and 'ls'. I don't seem to be able to 'pipe' commands.
I type 'cd Documents | ls' whihc I think should open the Documents directory and list the files but all I get is the list of files at the root. If I enter the two commands seperately it works.
I'm assuming it is something to do with 'pipe' which I'm getting from a MacBook Pro UK keybaord by typing 'shift-\'.
I'm doing something dumb but what?
Thanks.

Answer 1

In the example you are using you would want semi-colon
cd Documents; ls
Or just
cd Documents
ls
A very common usage of pipe would be filter the output from the ls command
ls | grep -i "pdf"
which will give you a list of all the filenames that contain "pdf' in their name.  If you just want the files that end in "pdf" it would be
ls | grep -i "pdf$"
Of course you could do the same thing using a wildcard and the ls command alone
ls *.pdf
but filtering the output of another command can be much more complex than what a simple wildcard can generate, and not all commands will allow you to select exactly what they display.
You can do more than filter via a pipe, for example
ls *.pdf | while read variable
do
    mv "$variable" "My.$variable"
done
which would rename every pdf file so it starts with "My.".  Again more complicated operations can be crafted by  combining several commands into a single pipeline.  For example
cat tmp.txt | tr 'A-Z' 'a-z' | tr -cs 'a-z' '\n' | sort | uniq | comm -23 - /usr/share/dict/words
which will list all the tmp.txt words that do not exist in /usr/share/dict/words (this is a clasic pipeline created back in the early days of Unix).
Pipelines for fun an profit.
As Frank as suggested, spend some time looking at one of the Unix shell books at your local bookstore.  The shell (in this case 'bash') basics are pretty much the same for all flavors of Unix/Linux