List of extensions of filenames in bash script in one line

Question

I currently have the following line of code:

ls /some/dir/prefix* | sed -e 's/prefix.//' | tr '\n' ' '

Which does achieve what I want it to do:

• Get list of files starting with prefix
• Remove path and prefix from each string
• Remove newlines and replace with spaces for later processing.

For example:

/some/dir/prefix.hello
/some/dir/prefix.world

Should become

hello world

But I feel like there's a nicer way of doing this. Is there a better way to do this in one line?

Answer 1

Here is a two-liner using just built-ins that does it:

fnames=(some/dir/prefix*)
echo "${fnames[@]##*.}"

And here's how this works:

• fnames=(some/dir/prefix*) creates an array with all the files starting with prefix and avoids all the problems that come with parsing ls
• echo "${fnames[@]##*.}" is a combination of two parameter expansions: ${fnames[@]} prints all array elements, and the ##*. part removes the longest match of anything that ends with . from each array element, leaving just the extension

If you're hell-bent on a one-liner, just join the two commands with &&.