Problem scenario
You are trying to run very long, complex Linux commands. There are many case-sensitive flag options and convoluted DNS names. It takes time to hold the left arrow to go to the beginning of the command. Sometimes you want to comment out a line with a "#" at the beginning of the line as you draft these Linux commands.
Solution
Use ctrl-a to get to the first character of the command.
Conversely you may want to get to the end of the line immediately. Use ctrl-e to get to the last character of the command.
Remember that "#" (with no quotes) will comment out whatever is to the right of it. Therefore you can draft commands like this:
#Let me try to draft something with different flag options. I can always use Ctrl-A to get to the first line and Ctrl-E to the end of this long line before I press enter to run the command.
Ctrl-c will allow you to cancel out of a command without running it.