[hello] - one
[hello] - two
[hello] - three
[hello] - four

one
two
three
four

$ awk -F' *- *' '{ print $NF }' << EOF
> [hello] - one
> [hello] - two
> [hello] - three
> [hello] - four
> EOF
one
two
three
four

$ sed 's/^[hello] - //' << EOF
> [hello] - one
> [hello] - two
> [hello] - three
> [hello] - four
> EOF
one
two
three
four