How do I keep reading from a named pipe in Bash?

Question

I have created a named pipe

mkfifo ~/mypipe

and I write to it

echo "hello world" > ~/mypipe

and read from it

$ cat ~/mypipe
hello world

I have to retype cat ~/mypipe every time that I want to read it because it quits immediately. How do I keep reading from the pipe (and print to stdout) without manually running cat every time?

Answer 1

More than one option:

• with a loop:

  while true ; do cat ~/mypipe ; done

• with socat:

  socat /home/wonk/mypipe /dev/tty

• open the pipe for reading and writing with <>. The reader will get EOF only when the last writer to the pipe has closed. But since you're opening in both reading and writing, there will always be an open writer and it will never close:

  cat <> ~/mypipe

• a variant of the above is to open a given file descriptor for writing to the pipe:

  // open for reading
  cat ~/mypipe
  // redirect file descriptor to pipe
  exec 3> mypipe
  // write to file descriptor
  echo "hello world" >&3
  // close file descriptor, will send EOF
  exec 3>&-