TIL: bash subshell processing of data from stdin

coproc.sh

#!/usr/bin/bash
PID_MAIN=$$

# notify subshell on ctrl-c
trap "kill 0" SIGINT

# spawn processing subshell via coproc 
coproc WORK { while IFS= read x; do echo "  processed: $x" ; done }

PID_WORKER=$!

# spawn subshell that reads from processing coproc and prints to screen
( while IFS= read cooked; do 
    echo out: $cooked  
  done < /proc/${PID_MAIN}/fd/${WORK[0]}
) &

PID_WRITER=$!

# spawn subshell that forwards stdin to processing coproc
( while IFS= read x; do 
    echo in $x > /proc/${PID_MAIN}/fd/${WORK[1]} 
  done < /proc/${PID_MAIN}/fd/0 
) &

PID_READER=$!

sleep 3
echo "Data from main proc" >&${WORK[1]}


echo MAIN   ${PID_MAIN} 
ls -lFh /proc/${PID_MAIN}/fd/
echo WORKER ${PID_WORKER}
ls -lFh /proc/${PID_WORKER}/fd/
echo READER ${PID_READER}
ls -lFh /proc/${PID_READER}/fd/
echo WRITER ${PID_WRITER}
ls -lFh /proc/${PID_WRITER}/fd/


# main
echo "This is Main: A"
sleep 5

echo "This is main: B"
sleep 5

echo Done

# make sure the subshells die too
kill 0

Example: slowly feed some data into the script via stdin.

for i in {1..20}; do echo $i $(mktemp -u _XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX); sleep 1; done | ./coproc.sh