Rename multiple files based on pattern in Unix

Question

There are multiple files in a directory that begin with prefix fgh, for example:

fghfilea
fghfileb
fghfilec

I want to rename a

Answer 1

To install the Perl rename script:

sudo cpan install File::Rename

There are two renames as mentioned in the comments in Stephan202's answer. Debian based distros have the Perl rename. Redhat/rpm distros have the C rename.
OS X doesn't have one installed by default (at least in 10.8), neither does Windows/Cygwin.