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

Create md5sum of a directory

Shows space used by each directory of the root filesystem excluding mountpoints/external filesystems (and sort the output)
Excludes other mountpoints with acavagni's "mountpoint" idea, but with -exec instead of piping to an xargs subshell. Then, calling "du" only once with -exec's "+" option. The first "\! -exec" acts as a test so only those who match are passed to the second "-exec" for du.

Hypnosis
for OS X

Retrofit a shebang to an existing script
Function to add a shebang to an existing script, handy if you forgot to add it in the first place.

Watch the progress of 'dd'
This version was mentioned in the comments. Credits go to flatcap.

Check a server is up. If it isn't mail me.
Joker wants an email if the Brand X server is down. Set a cron job for every 5 mins with this line and he gets an email when/if a ping takes longer than 3 seconds.

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"

Delete specific sender in mailq

see the TIME_WAIT and ESTABLISHED nums of the network
see the TIME_WAIT and ESTABLISHED nums of the network


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