8.2. Reading User Input

The read command is a built-in command used to read input from the terminal or from a file (see Table 8.1). The read command takes a line of input until a newline is reached. The newline at the end of a line will be translated into a null byte when read. You can also use the read command to cause a program to stop until the user enters a carriage return. To see how the read command is most effectively used for reading lines of input from a file, see "Looping Commands" on page 349.

Example 8.3.


(The Script)

     #!/bin/sh

     # Scriptname: nosy

     echo "Are you happy? \c"

1    read answer

     echo "$answer is the right response."

     echo "What is your full name? \c"

2    read first middle last

     echo "Hello  $first"

------------------------------------------------------------

(The Output)

     Are you happy? Yes

1    Yes is the right response.

2    What is your full name? Jon Jake Jones

     Hello Jon

Table 8.1. The read Command
Format
Meaning
read answer
Reads a line from standard input and assigns it to the variable answer.
read first last
Reads a line from standard input to the first whitespace or newline, putting the first word typed into the variable first and the rest of the line into the variable last.

EXPLANATION

The read command accepts a line of user input and assigns the input to the variable answer.
The read command accepts input from the user and assigns the first word of input to the variable first, the second word of input to the variable middle, and all the rest of the words up to the end of the line to the variable last.

Example 8.4.


(The Script)

     #!/bin/sh

     # Scriptname: printer_check

     # Script to clear a hung up printer for SVR4

1    if [ $LOGNAME != root ]

     then

         echo "Must have root privileges to run this program"

         exit 1

     fi

2    cat << EOF

     Warning: All jobs in the printer queue will be removed.

     Please turn off the printer now. Press Enter when you

     are ready to continue. Otherwise press Ctrl-C.

     EOF

3    read ANYTHING      # Wait until the user turns off the printer

     echo

4    /etc/init.d/lp stop       # Stop the printer

5    rm -f /var/spool/lp/SCHEDLOCK /var/spool/lp/temp*

     echo

     echo "Please turn the printer on now."

6    echo "Press Enter to continue"

7    read ANYTHING            # Stall until the user turns the printer back on

     echo                     # A blank line is printed

8    /etc/init.d/lp start     # Start the printer

EXPLANATION

Checks to see if user is root. If not, sends an error and exits.
Creates a here document. Warning message is displayed on the screen.
The read command waits for user input. When the user presses Enter, the variable ANYTHING accepts whatever is typed. The variable is not used for anything. The read in this case is used to wait until the user turns off the printer, comes back, and presses Enter.
The lp program stops the printer daemon.
The SCHEDLOCK file must be removed before the scheduler can start again, as well as temporary files in /var/spool/lp.
The user is asked to press Enter when ready.
Whatever the user types is read into the variable ANYTHING, and when Enter is pressed, the program will resume execution.
The lp program starts the print daemons.

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