Reading from standard input

Shell Programming and Scripting
1

So, I am new to shell scripting and have a few problems.
I know how to read from standard input but I do not know how to really compare it to say, a character. I am trying to compare it to a character and anything exceeding just a character, the user will get an output message, but the program goes on.

I tried using test with regular expressions after taking an input like this.

read input

while test $input != q || test -z $input
do
        if test $input = n
        then
 ...

I also want my program to move on if the input just presses enter, but I get two error messages on the while statement and the if statement saying unary operator expected.

2

You need to check the length of a string, then.

There's really no reason to use test, at all, ever these days.

STR="zzz"

while [ "$#STR" -ne 1 ]
do
        printf "Enter one letter:   "
        read STR
done
3

May I ask the reason to not use test? I recognize the square brace as an alternative method, I'm just curious as I'm just starting to learn.

And # is?

4

Each time you run test you're creating a new process and waiting for it to quit. [ ] are usually shell built-ins these days, so no new process is needed -- meaning, hundreds of times faster.

# is length.

5

Corona,

I tried testing your code, and it says on the loop with the case statement "integer expression expected"

6

Corona probably meant

${#STR}

You could also do without testing for the length, just take the first character like this:

while [ ${STR:0:1} != q ] ; then ...
7

I'm sorry, but could you explain what the colons mean?

8

See this table.

Of course, if your shell isn't bash or ksh, you could have few or none of these.