rename(1) -- Linux man page
NAMErename - Rename files
SYNOPSISrename from to file...
DESCRIPTIONrename will rename the specified files by replacing the first occurrence of from in their name by to.
For example, given the files foo1, ..., foo9, foo10, ..., foo278, the commands
rename foo foo0 foo? rename foo foo0 foo??
will turn them into foo001, ..., foo009, foo010, ..., foo278.
rename .htm .php *.htm
will fix the extension of your html files.