Chris Fearnley on Sun, 9 Mar 1997 15:35:14 -0500 (EST)

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[PLUG] bash: process substitution

As it turns out, I don't understand bash's process substitution.  I
saw a ghost (as we say in chess after blundering).

Here's a quote from the bash man page in case anyone else has a clue:
   Process Substitution
       Process  substitution is supported on systems that support
       named pipes (FIFOs) or the /dev/fd method of  naming  open
       files.  It takes the form of <(list) or >(list).  The pro-
       cess list is run with its input or output connected  to  a
       FIFO  or  some  file in /dev/fd.  The name of this file is
       passed as an argument to the current command as the result
       of the expansion.  If the >(list) form is used, writing to
       the file will provide input for list.  If the <(list) form
       is  used, the file passed as an argument should be read to
       obtain the output of list.

Here is the script that I thought used process substitution (maybe it

mkfifo junkfifo1
until [ "$EX" = "QUIT" ]; do
  EX=$(cat <(cat junkfifo1 )); echo "Command: $EX"; done
[In another window "cat something > junkfifo1; cat QUIT > junkfifo1"]

And here is the modification I made that convinced me that I don't
know what I'm talking about:

until [ "$EX" = "QUIT" ]; do
  EX=$(cat < junkfifo1); echo "Command: $EX"; done

In both cases you can read from the FIFO and process the results.  But
the simpler syntax of my second attempt seems better to me.

I guess it's time to subscribe to gnu.bash ...

The FAQ suggests that maybe ksh88 coprocesses are like process
substitution.  Anyone know how coprocesses work?

Christopher J. Fearnley          |  Linux/Internet Consulting,     |  Design Science Revolutionary       |  Explorer in Universe  |  "Dare to be Naive" -- Bucky Fuller