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Optimal way of deleting huge numbers of files

find an unused unprivileged TCP port
Some commands (such as netcat) have a port option but how can you know which ports are unused?

Convert CSV to JSON
Replace 'csv_file.csv' with your filename.

Optimize Xsane PDFs
Xsane produces PDFs that are too large - particularly multipage PDFs. This command compresses them. If you do not use A4, remove the -sPAPERSIZE flag.

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"

Rename files in batch

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" }

Top 30 History
Top 30 History Command line with histogram display

Emptying a text file in one shot
% = buffer d = delete

convert unixtime to human-readable
Mac have direct conversion of seconds (Epoch time)


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