Process Substitution

This feature is only available on versions of the Unix operating system that support the /dev/fd directory for naming open files. Each command argument of the form <(list) or >(list) will run process list asynchronously connected to some file in /dev/fd. The name of this file will become the argument to the command. If the form with > is selected then writing on this file will provide input for list. If < is used, then the file passed as an argument will contain the output of the list process. For example,

paste <(cut –f file1) <(cut –f3 file2) | tee >(process1) >(process2)

cuts fields 1 and 3 from the files file1 and file2 respectively, pastes the results together, and sends it to the processes process1 and process2, as well as putting it onto the standard output. Note that the file, which is passed as an argument to the command, is a Unix system pipe(2) so programs that expect to lseek(2) on the file will not work.