Using a file input as stdin for a shell script does not work

Question

I have the following script code:

test.sh

echo "BEGIN"
while read CMD <&1; do
    [ -z "$CMD" ] && continue
    case "$CMD" in
    start)
            echo "get_start"
            ;;
    stop)
            echo "get_stop"
            ;;
    *)
            echo "get_uknown_command"
            ;;
    esac
    echo "END";
done

When I run it with:

$./test.sh <input.txt

I get my script locked

input.txt

start
stop
sthh

Why my script is locked? How I can fix that?

BTW: If I enter the data manually then the script will not lock.

Answer 1

Your second line is incorrect, and overly complex anyway. The file descriptors for stdin, stdout, and stderr are 0, 1, and 2, respectively, so to read from stdin you'd want to have

while read CMD <&0; do 

However, since stdin is the default input for read,

while read CMD; do

is really the simplest way to go. This way, you can manually enter the commands, or use redirection on the command line to read from a file.