sed

[fabrizio . gualandris]

Hallo, i have a problem with "sed" command:

i want to replace a " " character (blank) with "." character but a have
error.

For example :

"for example" must become "for.example"
My command is: sed s." ".".".g
error: sed: -e expression #1,char 6:Unknow option ti 's'.

Can you write the correct sequence command to do so?

Thanks for your help