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Enter a command but keep it out of the history
Put a space in front of your command on the command line and it will not be logged as part of your command line history.

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" }

Launch a command from a manpage
Launch a command from within a manpage, vim style. This is rather trivial, but can be very useful to try out the functions described in a manpage without actually quitting it (or switching to another console/screen/...).

Schedule a command while one is already running.
Useful when you have only one terminal session e.g. ssh. and want to queue up another command after the currently running has finished(in case if you forget to run that command). Originally used as ; python-updater when running emerge. When I have noticed that a package failed due to that command not run.

Rename files in batch

Set laptop display brightness
Run as root. Path may vary depending on laptop model and video card (this was tested on an Acer laptop with ATI HD3200 video). $ cat /proc/acpi/video/VGA/LCD/brightness to discover the possible values for your display.

List only directories, one per line

View non-printing characters with cat
Useful to detect number of tabs in an empty line, DOS newline (carriage return + newline). A tool that can help you understand why your parsing is not working.

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" }

Generate a binary file with all ones (0xff) in it
This is similar to how you would generate a file with all zeros $ dd if=/dev/zero of=allzeros bs=1024 count=2k


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