ksh协助进程

#!/bin/ksh
# Scriptname: mycalculator
# A simple calculator -- uses the bc command to perform the
# calculations
# Since the shell performs operations on integers only,
# this program allows
# you to use floating point numbers by writing to and reading
# from the bcprogram.

cat << EOF
**************************************************
     WELCOME TO THE CALCULATOR PROGRAM
*************************************************
EOF

bc |&               # Open coprocess

while true
do
 print "Select the letter for one of the operators below "
 cat <<- EOF
   a) +
   s) -
   m) *
   d) /
   e) ^
 EOF
 read op
 case $op in
     a) op="+";;
     s) op="-";;
     m) op="*";;
     d) op="/";;
     e) op="^";;
     *) print "Bad operator"
         continue;;
 esac
 print -p scale=3                    # write to the coprocess
 print "Please enter two numbers: "  # write to standard out
 read num1 num2                      # read from standard in
 print -p "$num1" "$op" "$num2"      # write to the coprocess
 read -p result                      # read from the coprocess
 print $result
 print -n "Continue (y/n)? "
 read answer
 case $answer in
 [Nn]* )

     break;;
 esac
done
print Good-bye