linux - Rename all files in a folder with a prefix in a single command
Rename all the files within a folder with prefix "Unix_" 

If your filenames contain no whitepace and you don't have any subdirectories, you can use a simple for loop:
$ for FILENAME in *; do mv $FILENAME Unix_$FILENAME; done 

Otherwise use the convenient rename command (which is a perl script) - although it might not be available out of the box on every Unix (e.g. OS X doesn't come with rename).
A short overview at debian-administration.org:

Easily renaming multiple files

If your filenames contain whitespace it's easier to use find, on Linux the following should work:
$ find . -type f -name '*' -printf "echo mv '%h/%f' '%h/Unix_%f\n'" | sh

On BSD systems, there is no -printf option, unfortunately. But GNU findutils should be installable (on e.g. Mac OS X with brew install findutils).
$ gfind . -type f -name '*' -printf "mv \"%h/%f\" \"%h/Unix_%f\"\n" | sh

