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Edit a script that's somewhere in your path.
Often I need to edit a bash or perl script I've written. I know it's in my path but I don't feel like typing the whole path (or I don't remember the path).

Debug your makefile
Say your dependencies specified in your Makefile (or dates on your source files) is causing 'make' to skip some source-files (that it should not) or on the other other end, if it is causing make to always build some source-files regardless of dates of target, then above command is handy to find out what 'make' thinks of your date v/s target date-wise or what dependencies are in make's view-point. The egrep part removes the extra noise, that you might want to avoid.

clean up syntax and de-obfuscate perl script
the command show can be run in vim, here is the same thing on the command line $ cat script.pl | perl -MO=Deparse | perltidy

how to export a table in .csv file
Exports the result of query in a csv file

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"

Using numsum to sum a column of numbers.
numsum is part of of the num-utils package, which is available in some Linux distros and can also be downloaded at http://suso.suso.org/xulu/Num-utils. It contains about 10 different programs for dealing with numbers from the command line. Obviously you can do a lot of things that the num-utils programs do in awk, sed, bash, perl scripts, but num-utils are there so that you don't have to remember the syntax for more complex operations and can just think: compute the sum, average, boundary numbers, etc.

merge multiple jpgs to one picture vertikal
# convert tool is from deb imagemagick-6.q16 apt install imagemagick-6.q16

mirrors directory to a ftp server
http://lftp.yar.ru/

Play all files in the directory using MPlayer
Skip forward and back using the < and > keys. Display the file title with I.

Remote copy directories and files through an SSH tunnel host
If you have lots of remote hosts sitting "behind" an ssh proxy host, then there is a special-case use of "rsynch" that allows one to easily copy directories and files across the ssh proxy host, without having to do two explicit copies: the '-e' option allows for a replacement "rsh" command. We use this option to specify an "ssh" tunnel command, with the '-A' option that causes authentication agent requests to be forwarded back to the local host. If you have ssh set up correctly, the above command can be done without any passwords being entered.


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