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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.

Manually Pause/Unpause Firefox Process with POSIX-Signals
Continue with: $killall -CONT -m firefox Suspends all Firefox Threads. Results in Zero CPU load. Useful when having 100+ Tabs open and you temporarily need the power elsewhere. Be careful - might produce RACE CONDITIONS or LOCKUPS in other processes or FF itself. matching is case sensitive.

Shows what processes need to be restarted after system upgrade
emerge,apt-get,yum... all update your system. This will at some point replace either a runtime dependency or a process (which is still running). This oneliner will list what processes need to be restarted

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"

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" }

Replaces a color in a PDF document, useful for removing a dark background before printing.
The pdf is first converted to a bitmap, so change "-density" to match your printer resolution. Also be careful about the RAM required. In this example rgb(0,0,0) is replaced by rgb(255,255,255), change to suit your needs.

Slightly better compressed archives
Avoids creating useless directory entries in archive, and sorts files by (roughly) extension, which is likely to group similar files together for better compression. 1%-5% improvement.

Most used command

Kill google chrome process

Watch the National Debt clock
The idea was originally stolen from Linux Journal. 'wget' pulls the debt clock and 'sed' reformats it for general consumption. Prefacing the command with 'watch' simply sets an interval - in this case every 10 seconds.


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