How can I rename directories that start with a bracketed year in Bash?

Bash can capture the year and title directly with BASH_REMATCH. Run this from the parent directory:

for dir in */; do name=${dir%/} if [[ $name =~ ^(\[([0-9]{4})\]|\(([0-9]{4})\))\ (.*)$ ]]; then year=${BASH_REMATCH[2]:-${BASH_REMATCH[3]}} title=${BASH_REMATCH[4]} printf 'mv -- %q %q\n' "$name" "$year - $title" fidone

That prints the proposed commands without changing anything. After checking them and making sure the destination names do not already exist, replace the printf line with mv -- "$name" "$year - $title". The quotes keep spaces and other special characters in each name intact.

For a manageable batch, vidir from moreutils is another option. It opens a directory listing in an editor, and you can edit the names there before saving. That gives you a chance to check the changes visually without writing a shell loop.

I would avoid deleting every bracket, parenthesis, or space with tr. Those characters might also be part of a title, so a broad replacement could change more than the year prefix. Match the prefix specifically and leave the rest of the name alone.