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print code 3-up and syntax-highlighted for easy beach-time study
This is the setup I'm using for my largest project. It gives 357 lines per page (per side), which makes it fairly easy to carry around a significant amount of code on a few sheets of paper. Try it. (I stick to the 80 column convention in my coding. For wider code, you'll have to adjust this.)

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"

Suspend an ssh session.
This must be typed before any other characters have been entered on the line. Use fg, as usual, to resume the ssh session.

List the size (in human readable form) of all sub folders from the current location
Sorted in human readable format.

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

find all active IP addresses in a network
You send a unicast ICMP packet to each host. Many firewalls will drop that ICMP. However, in order to send the ICMP, you'll have first done an ARP request and the remote machine is unlikely to ignore that, so the computer will be in your ARP table.

Remove trailing space in vi

convert single digit to double digits
each number in a file name gets expanded to the number of digets provided as arg_1 of the arguments in rjust_file_nums. Put the funciton in the .bashrc file. Be sure to $ source ~/.bashrc so that the function will be accessible from bash.

"at" command w/o the resource usage/competition issues
EXAMPLES jb "next sun 12pm" "/bin/sh ~you/1.sh" & jb "2010-08-29 12:00:00" "~you/1.sh" & jb "29aug2010 gmt" ". ~you/1.sh" & jb 12:00p.m. "nohup ./1.sh" & jb 1min "echo stop!" & SEE ALSO parsedate(3) strftime(3)

get all bookmarks from all profiles from firefox
for i in $(ls /home/marco/.mozilla/firefox/*\.*/places.sqlite); do sqlite3 $i "SELECT strftime('%d.%m.%Y %H:%M:%S', dateAdded/1000000, 'unixepoch', 'localtime'),url FROM moz_places, moz_bookmarks WHERE moz_places.id = moz_bookmarks.fk ORDER BY dateAdded;"; done


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