demo5

#!/bin/bash

coproc dialogbox    # Note: bash supports only one co-process
INPUTFD=${COPROC[0]}  # file descriptor the dialogbox process writes to
OUTPUTFD=${COPROC[1]}  # file descriptor the dialogbox process reads from
DBPID=$COPROC_PID    # PID of the dialogbox, if you need it for any purpose... e.g. to kill it

# If your script doesn't use standard input/output you may redirect them to the pipes
# and don't bore with redirection for each input/output command.
# Tools used might output something to the pipe but it is unlikely it will be understood by the
# dialogbox application. So, this is 99.99% safe...
# The following two commands will do the job:
#  exec <&${COPROC[0]}
#  exec >&${COPROC[1]}

# Exit status values:
E_SUCCESS=0
E_CANCEL=1

# The trap checks whether the dialogbox application was terminated and if so
# kills the current job and exits the script
trap "if ! kill -0 $DBPID &>/dev/null; then kill %; echo The script cancelled by user; exit $E_CANCEL; fi" CHLD
set -o monitor  # Enable SIGCHLD

cat >&$OUTPUTFD <<EODEMO
add label "<small>This script demonstrates the dialogbox application monitoring technique during bidirectional communication with it using pipes." note
set note stylesheet "qproperty-textInteractionFlags: NoTextInteraction;"
add separator
add label "Click Next to start a long-run process" msg
set msg stylesheet "min-width: 20em;"
add frame horizontal
add stretch
add pushbutton &Next okay
add pushbutton &Cancel cancel exit
end frame
set title "Demo 5"
set okay default
set okay focus
EODEMO

while IFS=$'=' read key value
do
  case $key in
    okay)
      echo User initiated the long-run process
      break
      ;;
  esac
done <&$INPUTFD

cat >&$OUTPUTFD <<EODEMO
set msg title "The long-run process is in progress.<br>Please wait..."
remove okay
set cancel default
set cancel focus
EODEMO

# The long-run process is run in background to return control to the shell
# to allow it process signals immediately
sleep 10&
wait %
echo The long-run process completed

cat >&$OUTPUTFD <<EODEMO
set msg title "The long-run process completed!"
set cancel title &Ok
EODEMO

set +o monitor  # Disable SIGCHLD
wait $DBPID    # Wait the user to complete the dialog

echo The script completed successfuly

exit $E_SUCCESS