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List directories recursively showing its sizes using only ls and grep
ls -lhR Lists everithing using -l "long listing format" wich includes the space used by the folder. Displays it in -h "human readable form" (i.e. 2.2G, 32K), and -R recurses subfolders. grep -e using a regex, show lines containing the word "total" or a ":" at the end of the line (those with the name of the folder) only.

Check if it's your binary birthday!
Print out your age in days in binary. Today's my binary birthday, I'm 2^14 days old :-) . This command does bash arithmatic $(( )) on two dates: Today: $(date +%s) Date of birth: $(date +%s -d YYYY-MM-DD) The dates are expressed as the number of seconds since the Unix epoch (Jan 1970), so we devide the difference by 86400 (seconds per day). . Finally we pipe "obase=2; DAYS-OLD" into bc to convert to binary. (obase == output base)

Read and write to TCP or UDP sockets with common bash tools
Ever needed to test firewalls but didn't have netcat, telnet or even FTP? Enter /dev/tcp, your new best friend. /dev/tcp/(hostname)/(port) is a bash builtin that bash can use to open connections to TCP and UDP ports. This one-liner opens a connection on a port to a server and lets you read and write to it from the terminal. How it works: First, exec sets up a redirect for /dev/tcp/$server/$port to file descriptor 5. Then, as per some excellent feedback from @flatcap, we launch a redirect from file descriptor 5 to STDOUT and send that to the background (which is what causes the PID to be printed when the commands are run), and then redirect STDIN to file descriptor 5 with the second cat. Finally, when the second cat dies (the connection is closed), we clean up the file descriptor with 'exec 5>&-'. It can be used to test FTP, HTTP, NTP, or can connect to netcat listening on a port (makes for a simple chat client!) Replace /tcp/ with /udp/ to use UDP instead.

Find the package that installed a command

bash pause command
Just added -sn1 -s = silent -n1 = only one symbol needed to continue after the insert

Get sunrise and sunset times
This will get the sunrise and sunset times of a specific location. To be able to determine $l you need to first go to http://weather.yahoo.com/ and look up your location. The last numbers in the URL will be the $l Instead of forecastrss?w=$l you can also use forecastrss?p=$l and use the RSS link of the city you found. Also see http://developer.yahoo.com/weather/ for more information

Connect to FreeWifi hotspot (France) and keep the connection active
(In French) Connection aux hotspots FreeWifi, et maintien de la connection active

An alias to re-run last command with sudo. Similar to "sudo !!"
I didn't come up with this myself, but I always add this to my .bash_aliases file. It's essentially the same idea as running "sudo !!" except it's much easier to type. (You can't just alias "sudo !!", it doesn't really work for reasons I don't understand.) "fc" is a shell built-in for editing and re-running previous commands. The -l flag tells it to display the line rather than edit it, and the -n command tells it to omit the line number. -1 tells it to print the previous line. For more detail: $help fc

Waste time for about 3 minutes
If you're a slow reader and/or you like to ponder, adjust the sleep time to be longer

return external ip
curl inet-ip.info -> 113.33.232.62\n curl inet-ip.info/ip -> 113.33.232.62 curl inet-ip.info/json -> JSON print curl inet-ip.info/json/indent -> JSON pretty print curl inet-ip.info/yaml -> YAML format curl inet-ip.info/toml -> TOML format http://inet-ip.info


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