Get your sha1 signature/hash of a file with shasum:

shasum ./somefile.ext

You can find documents/files/stuff using the find command:

find . -name "blah"

Find out which ports are being used by system processes using netstat:

netstat -an | grep 8080

You can stack commands (like ps and grep) as in this case:

ps aux | grep tomcat

Here, ps (process snapshot) is displaying processes using the following parameters…

a = show processes for all users
u = display the process’s user/owner
x = also show processes not attached to a terminal

… that is “piped” (using the “|” operator) to grep which filters the results to give you only those that have "tomcat" within them.

Similarly, you can route output from a command into a file, rather than displaying it in the terminal. Consider this example: cat (concatenate) with

cat *.txt > gratuitously-concatenated-file.text

This will put the contents all of the matching text files (any with the .txt file extension in the same current directory) into a file called gratuitously-concatenated-file.text. But if you are working in the same directory, don’t call the file by the same name as what you are concatenating (when using so greedy a wildcard), because it will recursively add itself to itself until the disk is consumed.