In bash, can the file operator (-f) be case-insensitive?

not knowing howto only using shell evaluations. but grep can be case-insensitive, therefore a script that invokes grep , find and wc may meet your demand.

The problem is that your filesystem is case-sensitive. The filesystem provides only two relevant ways to get a file: either you specify an exact, case-sensitive filename and check for its existence that way, or you read all the files in a directory and then check if each one matches a pattern.

In other words, it is very inefficient to check if a case-insensitive version of a file exists on a case-sensitive filesystem. The shell might do it for you, but internally it's reading all the directory's contents and checking each one against a pattern.

Given all that, this works:

if [[ -n $(find /etc -maxdepth 1 -iname passwd) ]]; then
  echo "Found";
fi

BUTunless you want to search everything from '/' on down, you must check component of the path individually. There is no way around this; you can't magically check a whole path for case-insensitive matches on a case-sensitive filesystem!