virtual file

Bash has a cool feature, it allows you to redirect the output of an application to a virtual file. With this its for example possible to fast-diff two directories. The old way would look like this: ls dir1/ > directory_1.txt ls dir2/ > directory_2.txt diff directory_1.txt directory_2.txt But with bash (and maybe some other shells) you can do the following: diff <(ls dir1/) <(ls dir2/)