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 "*.txt"

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 a 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.txt

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.txt. 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.

source will reload the contents of your bash profile. One use case for this is not having to start a new session just to realize changes made to a particular path variable.

$ source ~/.bash_profile

OR

$ . ~/.bash_profile