Commands by rsimpson (3)

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Show the 1000*1000 and 1024*1024 size of HDs on system

List only directories, one per line

Deal with dot files safely

Clear terminal Screen
Probably the quickest / easiest way to clear the screen.

output your microphone to a remote computer's speaker

Generate a random text color in bash
The expression $(( $RANDOM * 6 / 32767 + 1 )) generates a random number between 1 and 6, which is then inserted into the escape sequence \e[3_m to switch the foreground color of the terminal to either red, green, yellow, blue, purple or cyan. The color can be reset using the escape sequence \e[0m. The full list of colors can be found here: https://wiki.archlinux.org/index.php/Color_Bash_Prompt#List_of_colors_for_prompt_and_Bash

Retry the previous command until it exits successfully
Repeat the previously used command (!!) until it exits with a success code (0). To put a delay between attempts you could do something like $ until !!; do sleep 5; done to wait 5 seconds after each attempt.

Delete files older than..
This command will delete files i a given path (/dir_name) , which older than given time in days (-mtime +5 will delete files older than five days.

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" }

get all Google ipv4 subnets for a iptables firewall for example
a bit shorter, parenthesis not needed but added for clarity


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