Process Substitution and Named Pipes

Process Substitution and Named Pipes

Process substitution runs commands and exposes their output as a temporary file descriptor path (e.g. /dev/fd/63):

# Diff the output of two commands without temporary files on disk
diff -u <(systemctl list-unit-files --state=enabled) <(ssh remote-node systemctl list-unit-files --state=enabled)

# Named Pipes (FIFOs):
mkfifo /tmp/myfifo
# Process 1 writes: cat /dev/urandom > /tmp/myfifo &
# Process 2 reads:  head -c 100 < /tmp/myfifo
rm /tmp/myfifo