Rename some files with particular format

Question

I would like to rename some files. I have a lot of files with this format: ?????.pdb.

The name of this file is composed of 5 characters (numbers and letters) and the new name will be like this ????_biounit?.pdb. The first 4 characters of the old name must be preserved, while the fifth must be inserted after the word "biounits".

Some examples:

• Original files:

  1b471.pdb 1caz4.pdb 1ca93.pdb
  

• New files:

  1b47_biounit1.pdb 1caz_biounit4.pdb 1ca9_biounit3.pdb
  

I try to do it with the comand mv but I can't tell the difference between the first four characters and the fifth. Can someone help me please?

Answer 1

With a shell loop:

for f in ?????.pdb; do mv "$f" "${f%?.pdb}_biounit${f#????}"; done

• ${f%?.pdb} removes ?.pdb from the end of the file name.
• ${f#????} removes ???? from the beginning of the file name.

Answer 2

Using perl rename tool:

rename -n 's/(....)(.)/$1_biounit$2/' ?????.pdb

Remove -n if you're happy with the output.