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display a smiling smiley if the command succeeded and a sad smiley if the command failed
you could save the code between if and fi to a shell script named smiley.sh with the first argument as and then do a smiley.sh to see if the command succeeded. a bit needless but who cares ;)

Link a deep tree of files all into on directory
If you want to pull all of the files from a tree that has mixed files and directories containing files, this will link them all into a single directory. Beware of filesystem files-per-directory limits.

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)

Install pip with Proxy
Installs pip packages defining a proxy

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"

Quick calculator at the terminal
Useful for quick calculations at the command line. $math_expr is any arithmetic expression (see sample output): 4.5*16+3^2 s(3.1415926/2) More options in the bc man page.

Set all CPU cores' CPU frequency scaling governor to maximum performance

Use file(1) to view device information
file(1) can print details about certain devices in the /dev/ directory (block devices in this example). This helped me to know at a glance the location and revision of my bootloader, UUIDs, filesystem status, which partitions were primaries / logicals, etc.. without running several commands. See also: $ file -s /dev/dm-* $ file -s /dev/cciss/* etc..

Commandline document conversion with Libreoffice
In this example, the docx gets converted to Open Document .odt format. For other formats, you'll need to specify the correct filter (Hint: see "Comments" link below for a nice list).

Convert seconds to [DD:][HH:]MM:SS
Converts any number of seconds into days, hours, minutes and seconds. sec2dhms() { declare -i SS="$1" D=$(( SS / 86400 )) H=$(( SS % 86400 / 3600 )) M=$(( SS % 3600 / 60 )) S=$(( SS % 60 )) [ "$D" -gt 0 ] && echo -n "${D}:" [ "$H" -gt 0 ] && printf "%02g:" "$H" printf "%02g:%02g\n" "$M" "$S" }


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