Posix shell scripting... prompting for a response from within a "while read" loop

[Kurt Renner]

Consider the following code:

find / ! -fstype nfs -only -perm -o+w -type d | while read line; do
echo "Do you want to change permissions on file ${line## *}."
read answer
done

I understand why this doesn't give me the results I am looking for. The line "read answer" is loading the answer variable with the next line from the "find... " command.

How can I prompt for and read a response from the user blocking stdin from the "find .." command until I "read" a response from the user?

I thought putting a section of code withing parenthesis should fork a child process outside the influence of stdin from the parent process, but it does not appear that is the case.

Any ideas would be appreciated.

[James R. Ferguson · Accepted solution]

Hi Kurt:

You need to establish another file descriptor to accomodate the read within the loop.

#!/usr/bin/sh
exec 3<&0
while read LINE
do
echo $LINE
read -u3 REPLY
echo "you said $REPLY"
done < /etc/hosts

Regards!

...JRF...

[steven Burgess_2]

Hi

To create variable using read command you need

\c at the end of your echo within quotes ""

Is that what you mean ? -

I had a little trouble understanding exactly what you are after

Steve

[Darrell Allen]

Hi,

Try this:

find / ! -fstype nfs -only -perm -o+w -type d | while read line; do
echo "Do you want to change permissions on file ${line## *}."
read answer <&1
done

Darrell

[John Poff]

Hello Kurt,

I have a favorite script that might solve your problem. The script has a function that takes yes/no input. You might do something like this:

# Get a yes/no answer to a question. Exit status 0 if "yes"
# Allow a -y or -n switch to give the default answer on just a newline
function getyesno
{
typeset ans
typeset default
if [[ ${1-} = -y ]] ; then default=0 ; shift ;
elif [[ ${1-} = -n ]] ; then default=1 ; shift ;
fi
while true
do
print -n >&2 "$@ "
read <&2 ans
case $ans in
[Yy]*) return 0 ;;
[Nn]*) return 1 ;;
?*) ;;
*) # Answer was just
if [[ ! -z $default ]] ; then return $default ; fi
;;
esac
print >&2 " Please answer yes or no"
done
}


find / ! -fstype nfs -only -perm -o+w -type d | while read file
do
if $(getyesno -y "Do you want to change permissions on file $file [y]")
then
chmod o-w $file
fi
done





Or something like that.

JP

[Kurt Renner]

James and Darrell had the answers I was looking for. Both solutions worked. Thanks! I knew there was a way to do it, but couldn't figure it out. In the past, I would always load an array first, if it was a short list, and then cycle through the array in a separate loop to prompt for answers.

In this case, the array subscripts could easily go beyond 1024 elements which made array usage a poor choice.

Thanks again!