Reading a single character from a file or a terminal

read reads a line of text at a time, but it is often useful to have a script wait for a keystroke, then act on that keystroke immediately. For example, when using a menu driven program, you may not want the program to wait for you to press <Enter> after you select an item. There is no command to obtain a single character from a terminal, but we can simulate one.

Here is a simple function to obtain a keystroke:

   getc ()
   {
     stty raw
     tmp=`dd bs=1 count=1 2>/dev/null`
     eval $1='$tmp'
     stty cooked
   }

   echo "Enter a character: \c"
   getc char
   echo
   echo "You entered $char"

The dd command reads a single character from the standard input and writes it to the standard output, that is captured in the variable tmp. The next line is used to assign the literal contents of tmp to the variable named by $1. The eval command in front of this line is necessary to force the shell to scan the line twice; once to expand $1 into the name of a variable, and again to carry out the actual command. The quotes around $tmp are stripped off by eval; if you omit them, then if your character is a whitespace character, it will be lost.

Afterwards, getc puts the terminal back into normal operating mode with the command stty cooked (or stty -raw, or stty sane).

We can write getc more succinctly like this:

   getc ()
   {
     stty raw
     eval $1=´`dd bs=1 count=1 2>/dev/null`´
     stty cooked
   }

   press_any_key()
   {
     echo "Strike any key to continue ...\c"
     getc anychar
   }

   getc ()
   {
     stty raw
     eval $1=´`dd bs=1 count=1 2>/dev/null`´
     stty cooked
   }
   press_any_key()
   {
     echo "Strike any key to continue ...\c"
     getc anychar
   }
   echo "Enter a character: \c"
   getc char
   echo
   echo "You entered $char"
   press_any_key char
   echo \r

   $ ./char_handler
   Enter a character: x
   You entered x
   Strike any key to continue ...y
   $