We know that we can use a pipe to provide the output of a command as an input to another command. For example:

$ cat file.txt | less

Here, the cat command output—that is, the content of file.txt—is passed to the less command as an input. We can redirect the output of only one process (cat process in this example) as an input to another process.

We may need to feed the output of multiple processes as an input to another process. In such a case, process substitution is used. Process substitution allows a process to take the input from the output of one or more processes rather than a file.

The syntax of using process substitution is as follows:

To substitute input file(s) by list

<(list)

OR

To substitute output file(s) by list

>(list)

Here, list is a command or a pipeline of commands. Process substitution makes a list act like a file, which is done by giving list a name and then substituting that name in the command line.