Bash – How to perform command substitution before brace expansion

The brace expansion you're asking about will only expand for files/directories that match on disk to the pattern you use. The other issue you'll run into is diskutil may not be able to handle more than 1 argument at a time. To expand these you'd need to do a while or for loop, and pass the results to diskutil as you iterate through the loop.

Example

$ for i in /dev/*; do diskutil "$i";done

As to your 2nd question there isn't really any method where brace expansion can help you in situations where there are no corresponding files/directories on disk.

Parsing diskutil

Given the output from this command you'll have to resort to using a tool such as awk, sed, or grep to "parse" this output so that you can get meaningful information about the disks, for further queries calling diskutil a 2nd time.

Example

Here's a rough cut of parsing the output from diskutil using grep and sed. There are more efficient ways to do this but this shows you the general approach.

$ diskutil list | grep -E "[ ]+[0-9]+:.*disk[0-9]+" | sed 's/.*\(disk.*\)/\1/'
disk0
disk0s1
disk0s2
disk0s3

With this approach you can then modify the for loop above like so:

$ for i in $(diskutil list | grep -E "[ ]+[0-9]+:.*disk[0-9]+" | \
    sed 's/.*\(disk.*\)/\1/'); do diskutil info $i; done

The brace expansion syntax accepts commas, but it does not accept a space after the comma. In many programming languages, spaces after commas are commonplace, but not here. In Bash, the presence of an unquoted space prevents brace expansion from being performed.

Remove the space, and it will work:

cp ~/some/dir/{my-file-to-rename.bin,new-name-of-file.bin}

While not at all required, note that you can move the trailing .bin outside the braces:

cp ~/some/dir/{my-file-to-rename,new-name-of-file}.bin

If you want to test the effect of brace expansion, you can use echo or printf '%s ', or printf with whatever format string you prefer, to do that. (Personally I just use echo for this, when I am in Bash, because Bash's echo builtin doesn't expand escape sequences by default, and is thus reasonably well suited to checking what command will actually run.) For example:

ek@Io:~$ echo cp ~/some/dir/{my-file-to-rename,new-name-of-file}.bin
cp /home/ek/some/dir/my-file-to-rename.bin /home/ek/some/dir/new-name-of-file.bin