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Do a search-and-replace in a file after making a backup

Display the standard deviation of a column of numbers with awk

Display connections histogram
Displays a connection histogram of active tcp connections. Works even better under an alias. Thanks @Areis1 for sharing this one.

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 old a web page is
I used to use the Firefox "View page info" feature a lot to determine how stale the web page I was looking at was. Now that I use mostly Chrome I miss that feature, so here is a command line alternative using wget. The -S says to display the server response, the --spider says to not download any files/pages, just fetch the header. The output goes to stderr, so to grep it you use 2>&1 to combine the stderr stream with stdout, the pipe that to grep for Last-Modified. You can use curl instead if you have it installed, like this: $ curl --head -s http://osswin.sourceforge.net | grep Mod

Best SSH options for X11 forwarding
grabbed from: http://blog.samat.org/2006/05/08/best-ssh-options-for-x11-forwarding

Traceroute w/TCP to get through firewalls.
man tcptraceroute

execute a command in case of success or execute a command in case of failure

get useful statistics from tcpdump (sort by ip)
We can get useful statistics from tcpdump with this simple command. Thanks "Babak Farrokhi" to teaching me this ;)

find and remove old compressed backup files
remove all compressed files in /home/ folder not created in the last 10 days


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