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Block all IP addresses and domains that have attempted brute force SSH login to computer
Searches all log files (including archived bzip2 files) for invalid user and PAM authentication errors, both of which are indicative of brute force attempts at logging into computer. A list of all unique IP addresses and domain names is appended to hosts.deny. The command (and grep error messages) will work on Mac OS X 10.6, small adjustments may be needed for other OSs.

shutdown if wget exit

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Check if a machine is online with better UI
I have used single packet, and in a silent mode with no display of ping stats. This is with color and UI improvement to the http://www.commandlinefu.com/commands/view/10220/check-if-a-machine-is-online. It is as per the enhancements suggested.

create a nicely formatted example of a shell command and its output
Shell function which takes a bash command as its input, and displays the following formatted output: EXAMPLE: command OUTPUT: output from command

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

find out how many days since given date
You can also do this for seconds, minutes, hours, etc... Can't use dates before the epoch, though.

Unzip and untar a *.tar.gz file in one go to a specific directory
A *.tar.gz file needs to be unzipped & then untarred. Previously I might have unzipped first with $gunzip -d file.tar.gz and then untarred the result with $tar -xvf file.tar (Options are extract, verbose, file) Using the -z (decompress) option on tar avoids the use of gzip (or gunzip) first. Additionally the -C option will specify the directory to extract to.

Get your outgoing IP address
Instead of opening your browser, googling "whatismyip"... Also useful for scripts. dig can be found in the dnsutils package.

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"


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