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Use a var with more text only if it exists
See "Parameter Expansion" in the bash manpage. They refer to this as "Use Alternate Value", but we're including the var in the at alternative.

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" }

Pretty-print user/group info for a given user

recurisvely md5 all files in a tree
Found this little gem here: http://info.michael-simons.eu/2008/10/25/recursively-md5sum-all-files-in-a-directory-tree/

Extract your list of blocked images hosts from Firefox database
I use this to replicate my blocked images hosts list between work and home to keep my browsing ad-free.

Encode a string using ROT47
This command will encode a string using the ROT47 cipher.

Customize time format of 'ls -l'
the --time-style argument to 'ls' takes several possible modifiers: full-iso, long-iso, iso, locale, +FORMAT. The +FORMAT modifier uses the same syntax as date +FORMAT. --time-style=+"%Y-%m-%d %H:%M:%S" strikes a happy medium between accuracy and verbosity: $ ls -lart --time-style=long-iso doesn't show time down to the nearest second, $ ls -lart --time-style=full-iso displays time to 10E-9 second resolution, but with no significant digits past the full seconds, also showing the timezone: $ -rw-r--r-- 1 bchittenden bchittenden 0 2011-02-10 12:07:55.000000000 -0500 bar

Find usb device in realtime
Using this command you can track a moment when usb device was attached.

Mount partition from image (without offset mount)

external projector for presentations
i spent way too many hours trying to fiddle with /etc/X11/xorg.conf trying to hook up various external projectors. too bad i didn't know this would solve all my problems.


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