Suppose you have many html files which needs be backed up. In this case you can use the "rename" command.
# rename .html .html.bak *.html
The above command will rename all the files which have extension .html to .html.bak in the current directory.
# rename .html .html.bak *.html
The above command will rename all the files which have extension .html to .html.bak in the current directory.