If you have the rename
command available, you can use that:
rename 51fdda 2c3cd *tokudb
If you do not have the rename command available, you can do this with a simple loop:
for file in *51fdda*.tokudb; do
mv ${file} ${file/51fdda/2c3cd}
done
For more information about this second solution, see the "Brace Expansion" section of the bash(1)
man page.