mv command goes crazy

Question

Here is the script and I have singled out the block that I believe is causing the recent problem

mv sourcefile targetfile > /dev/null  

I know for a fact that mv will by default overwrite without asking for confirmation if the destination file exists. Therefore, the script (above) is right.

mv: try to overwrite `targetfile', overriding mode 0644 (rw-r--r--)?

The only time it will prompt/ask for confirmation to overwrite is with an –i option, which in this case is not used. It is not always happening. Just pops up once in a while

So, why is it behaving this way?

This is my mv version

mv (GNU coreutils) 8.12
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Mike Parker, David MacKenzie, and Jim Meyering.

Answer 1

According to man page, the -f option has this goal:

       -f, --force
          do not prompt before overwriting

Answer 2

I found the reason. It was due to permissions.

I have updated the directory permissions as chmod a+w <directory>

Other possible solutions are adding a rm -f targetfile before the mv command.

Ofcourse GHugo was correct to add -f option