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sort the contents of a text file in place.
sorts the contents of a file without the need for a second file to take the sorted output. This was previously entered as `sort -g list.txt -o $_` but as others have pointed out the $_ references the previous command. so this would've worked had that been the second part of a command joined with && like: cat list.txt && sort -g list.txt -o $_ The user below me Robin had the most correct command.

View all new log messages in real time with color

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" }

Clear your history saved into .bash_history file!
Note the space before the command; that prevents your history eliminating command from being recorded. ' history -c && rm -f ~/.bash_history' Both steps are needed. 'history -c' clears what you see in the history command. 'rm -f ~/.bash_history' deletes the history file in your home directory.

count total number of lines of ruby code
Adapted from http://stackoverflow.com/questions/1358540/how-to-count-all-the-lines-of-code-in-a-directory-recursively#answer-1359246

whowatch: Linux and UNIX interactive, process and users monitoring tool
whowatch is a interactive, ncurses-based, process and users monitoring tool, which updates information in real time. This is a perfect tool for local and remote servers. It displays information about the users currently logged on to the machine, in real-time. Besides standard information (login name, tty, host, user's process), the type of the connection (ie. telnet or ssh) is shown. Display of users command line can be switch to tty idle time. Certain user can be selected and his processes tree may be viewed as well as tree of all system processes. Tree may be displayed with additional column that shows owner of each process. In the process tree mode SIGINT and SIGKILL signals can be sent to the selected process. Killing processes is just as simple and fun as deleting lines on the screen.

Calculate days on which Friday the 13th occurs (inspired from the work of the user justsomeguy)
Friday is the 5th day of the week, monday is the 1st. Output may be affected by locale.

Print all fields in a file/output from field N to the end of the line

Count files beneath current directory (including subfolders)

Shows users and 'virtual users' on your a unix-type system
Shows a list of users that currently running processes are executing as. YMMV regarding ps and it's many variants. For example, you might need: $ ps -axgu | cut -f1 -d' ' | sort -u


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