1

I am using read for user input to perform some operation. The selector uses a two character test to print the appropriate information, without requiring the user to press ENTER after his input. Would it be possible to accept the q value to exit, because it is not composed of a two character selector.

  local done="false"
  while [ "$done" != "true" ]
  do
    echo ; read -n 2 lsk
    case $lsk in
     "1L")
        echo "$navaid_vscal"
        echo -e "$tacrgm"
        ;;
     q)
        done="true"  # ends while loop
        echo -n "$sgr"
        ;;
     *)
        ## repeats while do
        ;;
    esac
  done
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2 Answers 2

Reset to default
2

I don't believe the bash read built-in has that functionality. However you can implement a custom read command or function to achieve that.

For example, you can use this function:

read_or_quit(){
x=0;
while ((++x<=2)); do 
   read -n 1

   if [[ $REPLY = q ]]; then 
      echo q
      break
   else 
     echo -n "$REPLY"
   fi
done ; 
echo

# I thought that printing `echo` to `stdout` would
# append a new line which might break the `case` 
# functionality.
# echo >&2
}

And you can call the function by using $(read_or_quit) in your code:

local done="false"
  while [ "$done" != "true" ]
  do
    lsk=$(read_or_quit)
    case $lsk in
     "1L")
        echo "$navaid_vscal"
        echo -e "$tacrgm"
        ;;
     q)
        done="true"  # ends while loop
        echo -n "$sgr"
        ;;
     *)
        ## repeats while do
        ;;
    esac
  done
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8
  • What is the purpose of echo >&2 ? Commented Jan 27, 2023 at 4:57
  • @konmi For printing a break line to stderr. It's not necessary at all, you can simply use echo or just remove it. I used echo at the end of the function to avoid using this one after you call the function: lsk=$(read_or_quit). Commented Jan 27, 2023 at 5:06
  • What does it mean "to avoid using this one", what does "the one" refer to? Commented Jan 27, 2023 at 5:08
  • @konmi I meant echo, to avoid using echo. If you removed the echo a break line will not be printed. You can remove it and the code will work but the output might be ugly Commented Jan 27, 2023 at 5:13
  • Thank you for the clarification. I would have to keep it, although printing to stderr seems unimportant in my case. Why would you elect to send it to stderr ? Commented Jan 27, 2023 at 5:22
1

Split the read into an initial read (which leaves early when q is entered) and a subsequent one for the second character (I'll call them ch1 and ch2):

local done=false
until "$done"
do
    echo
    read -n 1 ch1
    if [ ch1 = q ]
    then
        printf %s "$sgr"  # More portable than echo -n
        break
    fi
    read -n 1 ch2
    case "$ch1$ch2" in
        1L)
            echo "$navaid_vscal"
            echo -e "$tacrgm"  # portability problem here!
            ;;
        *)
            ## repeats while do
            ;;
    esac
done

Obviously, the loop can be while true since nothing now sets done, but perhaps you'll need that in one of the case blocks, so I kept it. (I did change the string equality test to just running $done as a command, for simplicity)

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