diff two versions of a file that reside in different directories

Question

I would like to diff two versions of a file that reside in different directories, for example:

diff ./dirA/foo.txt ./dirB/foo.txt

I vaguely remember there is a way to write this in a more condensed way, so that the filename appears only once. Something like:

diff {./dirA/, ./dirB/}foo.txt

Anyone know how to do this?

Answer 1

Close. No space.

diff dir{A,B}/foo.txt

or, in the more likely case that the two folders don't actually have a common substring like that,

diff {dir,folder}/foo.txt

And, should you want to compare the whole tree, note that diff has a recursive (-r) option.