Internally, process substitution works by creating a named pipe (FIFO) or a temporary file that holds the output of the command specified within the parentheses. Here's a breakdown of how it functions:
-
Command Execution: When you use
<(...), Bash creates a subshell to execute the command inside the parentheses. -
Pipe Creation: Bash sets up a named pipe (or sometimes a temporary file) to capture the output of the command. This allows the output to be read as if it were a file.
-
File Descriptor: Bash provides a file descriptor that points to the named pipe or temporary file. This file descriptor is what you use in the main command (e.g.,
diff). -
Data Flow: The output of the command inside
<(...)is written to the pipe or temporary file, while the main command reads from it as if it were reading from a regular file. -
Cleanup: Once the main command completes, the named pipe or temporary file is removed, cleaning up any resources used.
This mechanism allows for efficient data handling without the need for explicit file management, enabling seamless integration of command outputs in scripts.
