Question

I’ve seen the technique before, but don’t know what it’s called and forget the exact syntax. Let’s say I need to pipe in a file to a program like: command < input-file. However, I want to directly pass these lines of the input file into the command without the intermediate input file. It looks something like this, but it doesn’t work:

command < $(file-line1; file-line2; file-line3)

Can someone tell me what this is called and how to do it?

Answer 1

This is called Process Substitution

command < <(printf "%s\n" "file-line1" "file-line2" "file-line3")

With the above, command will think its being input a file with a name much like /dev/fd/XX where ‘XX’ is some number. As you mentioned, this is a temporary file (actually a file descriptor) but it will contain the 3 lines you passed in to the printf command.