change default command options

One way would be by creating alias in your ~/.bashrc file:

alias l1='ls -1'

then by typing l1, ls -1 will be executed

In your Home directory, open .bashrc file in editor and add alias ls='ls -1'.

First open the terminal ( Press ControlAltT), enter gedit ./.bashrc to open your .bashrc file in the editor.

Find the section that has some aliases for ls. In mine (stock 11.10) it looks like:

# some more ls aliases
alias ll='ls -alF'
alias la='ls -A'
alias l='ls -CF'

Add the following line after the ls aliases:

alias ls='ls -1'

Save the file, exit gedit and the terminal and reboot. Now the ls command should execute ls -1 by default.

Just to clarify something to @RobDavenport answer. You can't use a function to override a command that has the same name.

e.g. to add a default param to the ls command you can do :

alias ls='ls -1 $@'

This will add a new alias called ls so it will be called instead of the original command. It will add the -1 option and forward every parameter $@ to the original ls command.

You could also do

function ls_column () {
  ls -1 $@
}

It would have the same effect but you must use a different name for your function. Otherwise it will call itself again and again.