Shell Programming and Scripting

I'm a complete UNIX newbie trying to write a simple shell script. The pseudo-code for the part I'm having trouble with is as such:

read something
while [ there is something ]; do this

The loop terminates at EOF (like when Ctrl+D is pushed) and displays the number of lines the user entered (kept in the loop as a variable that increments...easy). Thing is, I can't figure out how to set the loop condition to end when it reaches EOF (usually when the user pushes Ctrl+D). Any suggestions?

One idea, but it always helps to know what Shell you are using. If nothing else because there is variation on the syntax for echo.

Code:

counter=0
while true
do
        echo "Enter something: \c" ; read ans
        if [ "${ans}""X" = "X" ]
        then
                break
        fi
        counter=`expr ${counter} + 1`
done
echo "You answered ${counter} times"

Thanks, that actually works...but now I'd like to understand how it works. I think the line I'm most confused with is this one:

if [ "${ans}""X" = "X" ]
Is this the one that tests for EOF? I'm not quite sure what it's doing. All the other lines of script I seem to understand, except this one...

Alternatively:

Code:

i=0
while read ans
do 
  i=$(( i+1 ))
done
echo $i

When ctl-D is entered the value assigned to the variable ans is null. In this case, the if evaluates true because <nul>X is the same as Xand thus the loop is broken.

This is an alternative:

Code:

#!/usr/bin/env ksh
count=0
printf ">"
while read line
do
        printf ">"
        count=$((count+1))
done
echo "read $count lines"
exit

While will read from standard input until the end of the file and exit the loop without an explicit test. The only "odd" thing is the need to issue a prompt before the loop.

Code:

if [ "${ans}""X" = "X" ]

Because I don't know what Shell you are using I went for a syntax which works in most derivatives of the Bourne shell.

The syntax is avoiding a syntax error if the contents of ${ans} is blank. The variable ${ans} can be blank because the user pressed Enter or because the user typed Ctrl/D (unix end of file). When $[ans} is blank we are just comparing character "X" with character "X".

As Scrutinizer's post shows, in some shells you can do arithmetic in $(( )) variables. Depends what you have got available.

Well everything so far has worked. I think I'm using Fedora or Red Hat Linux...though I'm not 100% sure. I'd have to find out...

But thanks to all the responses so far, they've been a big help.