command line

Terminology – split screen terminal alternative to Terminator

terminology

If you are spending a lot of time in console, and have to manage multiple windows, there are a few options for you – screen, tmux, and, of course, Terminator. Recently, I’ve come across one more – Terminology.

Terminology is a console with built-in window multiplexing. It feels a bit more fancy than the options above and I enjoyed using it for about half a day. From then on, the look, feel, and unfamiliar mouse and keyboard behavior threw me back into the Terminator window. But f you were looking for an alternative to the well established options, here is one to try.

ASCII vs. ANSI

Browserling does it again:

For those of you not old enough, here are the ASCII and ANSI Wikipedia pages. Back in a day we used these for cool art, fancy user interfaces, email signatures, games and more. Have a look at some cool examples of ASCII art. Now imagine those “images” colored with the breathtaking variety of 8 colors and you’ve got yourself a true 90’s rainbow explosion.

You’d probably be surprised to learn that a lot of these have survived to modern day, and are still used in command line user interfaces.

P.S.: And if you think that this stuff is ancient, have a look at typewriter art example.

Easier AWS CLI with Docker

Here is a handy blog post that shows how to simplify the installation and running of the Amazon AWS command line commands, using Docker. With the Dockerfile like this:

FROM python:2.7
ENV AWS_DEFAULT_REGION='[your region]'
ENV AWS_ACCESS_KEY_ID='[your access key id]'
ENV AWS_SECRET_ACCESS_KEY='[your secret]'
RUN pip install awscli
CMD /bin/bash

One can build the image and run the container as follows:

$ docker build -t gnschenker/awscli
$ docker push gnschenker/awscli:latest
$ docker run -it --rm -e AWS_DEFAULT_REGION='[your region]' -e AWS_ACCESS_KEY_ID='[your access ID]' -e AWS_SECRET_ACCESS_KEY='[your access key]' gnschenker/awscli:latest

Obviously, DO NOT hardcode your Amazon AWS credentials into an image, which will be publicly available through DockerHub.

Once the AWS CLI works for you, you can add the command to your bash aliases, to make things even easier.

git: history of a source code line

git is one of those tools that no matter how much you know about it, there is an infinite supply of new things to learn. Here’s a handy bit I’ve discovered recently, thanks to this StackOverflow comment:

Since Git 1.8.4, git log has -L to view the evolution of a range of lines.

[…]

And you want to know the history of what is now line 155.

Then, use git log. Here, -L 155,155:git-web–browse.sh means “trace the evolution of lines 155 to 155 in the file named git-web–browse.sh“.

Absolutely brilliant! I used to suffer through this via an iteration of git blame and git show to the point of custom bash scripts.

Troubleshooting with /dev/tcp and /dev/udp

Imagine you are on a freshly installed Linux machine with the minimal set of packages, and you need to test network connectivity. You don’t have netcat, telnet, and your other usual tools. For the sake of the example, imagine that even curl and wget are missing. What do you do?

Well, apparently, there is a way to do this with plain old bash. A way, which I didn’t know until today. You can do this with /dev/tcp and /dev/udp. Here is an example verbatim from the Advanced Bash-Scripting Guide:

#!/bin/bash
# dev-tcp.sh: /dev/tcp redirection to check Internet connection.

# Script by Troy Engel.
# Used with permission.
 
TCP_HOST=news-15.net       # A known spam-friendly ISP.
TCP_PORT=80                # Port 80 is http.
  
# Try to connect. (Somewhat similar to a 'ping' . . .) 
echo "HEAD / HTTP/1.0" >/dev/tcp/${TCP_HOST}/${TCP_PORT}
MYEXIT=$?

: <<EXPLANATION If bash was compiled with --enable-net-redirections, it has the capability of using a special character device for both TCP and UDP redirections. These redirections are used identically as STDIN/STDOUT/STDERR. The device entries are 30,36 for /dev/tcp: mknod /dev/tcp c 30 36 >From the bash reference:
/dev/tcp/host/port
    If host is a valid hostname or Internet address, and port is an integer
port number or service name, Bash attempts to open a TCP connection to the
corresponding socket.
EXPLANATION

   
if [ "X$MYEXIT" = "X0" ]; then
  echo "Connection successful. Exit code: $MYEXIT"
else
  echo "Connection unsuccessful. Exit code: $MYEXIT"
fi

exit $MYEXIT