mv [man page] - move (rename) files
mv [OPTION]... [-T] SOURCE DEST
mv [OPTION]... SOURCE... DIRECTORY
mv [OPTION]... -t DIRECTORY SOURCE...
-f, --force
do not prompt before overwriting
-i, --interactive
prompt before overwrite
Move whole directory:
mv dir2/ dir1/

move content of dir2 to dir1:
mv dir2/* dir1/

Use -i option if you re not sure that the target directory does not contain same files or directories. If it does mv will override current files by default.:
mv -i file1 dir1/

mv command can be also used to rename files and directories:
mv file1 file2
