topic question on scripting in Operating System - Linux

question on scripting

Mark Harshman_1 — Fri, 31 Mar 2006 09:41:47 GMT

i'm trying to issue a prompt in a script, that will require a y/n response before contining. SO far, no luck. ANy help would be appreciated. thanks

Re: question on scripting

Pete Randall — Fri, 31 Mar 2006 09:44:21 GMT

You need to use "read":

echo "enter yes or no"
read ANSWER

You can then test the variable for "yes" or "no".

Pete

Re: question on scripting

Shahul — Fri, 31 Mar 2006 09:46:35 GMT

Hi,

This will do what you are looking for.

read answer
if [ $answer = "Y" ]
then
do this
else
do this
fi

You can also use case statment.

Hope this helps.

Shahul

Re: question on scripting

James R. Ferguson — Fri, 31 Mar 2006 09:47:03 GMT

Hi Mark:

#/usr/bin/sh
echo "Say something"
read REPLY
echo "You said ${REPLY} ...thank you!"
exit 0

Regards!

...JRF...

Re: question on scripting

Mark Harshman_1 — Fri, 31 Mar 2006 09:51:49 GMT

the echo statement prints the message, but doesnt pause for a reply, what am i missing? thanks

Re: question on scripting

James R. Ferguson — Fri, 31 Mar 2006 10:13:30 GMT

Hi Mark:

The 'read' waits for input.

#!/usr/bin/sh
typeset -l REPLY
echo "Answer 'y' or 'n' \c"
read REPLY

while [ "${REPLY}" != "y" -a "${REPLY}" != "n" ]
do
echo "Please answer 'y' or 'n'"
read REPLY
done
echo "You replied '${REPLY}' -- thanks!"
exit 0

...In the above script we keep asking for a REPLY until the user responds with a "y" or an "n". The 'typeset -l' causes the contents of the REPLY variable which is filled by the 'read' to be translated to lowercase letters. This makes the comparisons for a proper response easy.

Regards!

...JRF...

Re: question on scripting

A. Clay Stephenson — Fri, 31 Mar 2006 10:21:08 GMT

The read command should pause and wait form input; however, a few things could make it not do this:

1) You have redirected stdin.
2) There are already characters in the input buffer so the reply is being satisfied from the buffer.
3) No read permission on the stdin device.
4) You have changed the terminal characterics so that it times out if no characters are available.

Re: question on scripting

Mark Harshman_1 — Fri, 31 Mar 2006 10:25:04 GMT

ok, i am trying to use this within a read-while-do setup. I am trying basically reading a file, and asking the user if they want to proceed with the entry printed. Doing the "echo" and "read" within this does not seem to work. is there a way i can still do this within my existing read-while-do? am i confusing the issue? thanks

Re: question on scripting

James R. Ferguson — Fri, 31 Mar 2006 10:32:50 GMT

Hi Mark:

If you are issuing a 'read' to collect a user's input and are already reading a file, you will need to use *separate* file descriptors to keep the data segregated.

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

If the above example, I'm reading LINEs from the '/etc/hosts file; echoing them to STDOUT; and *read*ing from STDIN into the REPLY variable. The 'read -u' variation says that I want that read to be from file descriptor #3 which is a duplicate of descriptor zero (0) [STDIN] the beginning of the script.

Regards!

...JRF...

Re: question on scripting

Rodney Hills — Fri, 31 Mar 2006 10:35:41 GMT

It sounds like you redirect input with the while loop. You can force read to read from another device then STDIN.

read REPLY <&2

This will force read to read from STDERR which should still be assigned to your terminal.

Or if STDERR is redirected, then you can use-

read REPLY
HTH

-- Rod Hills

Re: question on scripting

Mark Harshman_1 — Fri, 31 Mar 2006 10:41:51 GMT

ok, the re-direct worked good, thanks. Now i have one more issue. If the answer is "n", i want to throw it back to my "cat-while-read" statement, if the answer is "y", i want to do a couple things before going back to the the "cat-while-read" statement. I obviously have this wrong cause its falling all the way thru. Thanks for your patience with a rookie scripter.

Re: question on scripting

James R. Ferguson — Fri, 31 Mar 2006 10:46:10 GMT

Hi Mark:

For loops you can 'break' or 'continue'.

A 'break' terminates the loop. A 'continue' will cause control to begin again at the top of the loop.

The manpages for 'sh-posix' are quite useful:

http://docs.hp.com/en/B2355-60127/sh-posix.1.html

Regards!

...JRF...

Re: question on scripting

Rodney Hills — Fri, 31 Mar 2006 11:01:04 GMT

With out seeing that section of code, it's hard to understand where you are coming from.

If the "read" is in the while-loop, then just follow with a structured if-

read REPLY if [[ "$REPLY" = "y" ]] ; then
echo "answer was y"
fi

HTH

-- Rod Hills