How do I make my own terminal command with flags?
Though the question is probably off-topic I want to provide an answer: to start with simple bash scripting get in touch with getopts.

#!/bin/bash

while getopts ":a:" opt; do
  case $opt in
    a)
      echo "I'm the $OPTARG coder in the world." &gt;&amp;2
      ;;
    \?)
      echo "Invalid option: -$OPTARG" &gt;&amp;2
      exit 1
      ;;
    :)
      echo "Option -$OPTARG requires an argument." &gt;&amp;2
      exit 1
      ;;
  esac
done


Save this bash script as coder in a directory in the PATH and make it executable with chmod +x coder. If you choose another name don't replace an already existing file with the same name! Choose a unique name! The bash script checks for the flag/option -a and takes the argument after the flag to echo a sentence. The script doesn't check if the result is grammatically correct!

Examples:

coder -a best will result in I'm the best coder in the world.
coder -a "most yellow" will result in I'm the most yellow coder in the world.

but:

coder -a most yellow will result in I'm the most coder in the world.

or

coder -b "most yellow" > Invalid option: -b.