RasPi Console and Screen

I kept having trouble connecting to the serial console of my Raspberry Pi using the Linux screen command. I could always connect to it from PuTTY on my Windows machine, but the Linux screen command... no.

Well, I found a command that worked.

"screen /dev/ttyUSB0 115200,cs8,-ixon"

 

So, hurray!!!

What is sed?

What have I learned about sed?

Well, it's a stream editor, meaning it edits text that's fed through it.

When using sed to edit, you use regex filters and commands to make changes to the text.

I learned that sed applies it's entire program (filters and commands) to each line. So, it's important to be careful how you write these. If applied in the wrong order, you may over-edit the line you are editing.

I've learned that sed sends its output to the operating system's standard output stream. This means that you need to redirect this output to a file if you want to preserve the edits. It's a good idea to send the output to a temporary file first and then overwrite the original once you have confirmed correct edits.

From IP to Hex and back again

 Did a one-liner to convert an IP address as a string into a string with 4 hex number pairs.

hexip=$(echo $ip | awk -F '.' '{printf "%02x%02x%02x%02x\n", $1,$2,$3,$4}')

Then from this string back to an IP address.

echo $hexip | grep -Eo '[A-Za-z0-9]{2}' | paste -s | awk -F '\t' '{printf "%d.%d.%d.%d","0x"$1,"0x"$2,"0x"$3,"0x"$4}'

Edit: It has occurred to me that given the fixed nature of the hexip string (it is always character pairs) there is no reason to grep and paste before using awk. Instead, this can all be done with one awk program.

echo $hexip | awk -F " " '{gsub(/../,"& "); printf "%d.%d.%d.%d","0x"$1,"0x"$2,"0x"$3,"0x"$4}'

IP and Grep to extract address

 This is just another one line command to extract a system IP address

ip -4 a show eth0 | grep -oP '(?<=inet\s)\d+(\.\d+){3}'

IP and JQ to extract address

 So I wanted to try to extract just the IP address of a named network adapter using bash. There are lots of ways to do this, but it turns out that the linux ip command supports output to JSON. This gets me thinking jq. After testing on Manjaro and Amazon Linux 2, this is the most reliable command I found.

ip -4 -j a | jq -r '.[] | select(.ifname | contains("eth0")) | .addr_info[].local'

Obviously the interface name is going to be different on different systems