How to run previous command with another command

Question

Say I do:

ls somedir

is there a way I could re-run it with a different command?

Example:

ls somedir
<run same command as above but with cd instead of ls>

Answer 1

The variable $_ is the last argument of the previous line you typed. So, for example, cd $_ would do what you described

bash-4.2$ ls X
1
bash-4.2$ cd $_
bash-4.2$ ls
1

There's also some command substitution options as well; eg ^ will replace commands on the previous line

bash-4.2$ ls X
1
bash-4.2$ ^ls^cd
cd X
bash-4.2$ ls
1