I beleive that you are asking how to rename files within a directory and not names in a file?? If that is the case, then use the script:
I've a folder with some files inside. Syntax: field.field.field.ext
But I would like to replace the . by _ or space.
We give me this command: sed -e 's/./_/g'
But I'm not an expert in script. But this will replace the point of my extensions too...
How can I do to replace only the point in the name and not the point of the extension in all files in one times?