topic Re: ctrl-d in while statement in Operating System - Linux

ctrl-d in while statement

Gemini_2 — Wed, 01 Mar 2006 16:16:27 GMT

I want to write a while statement to take user input, until user hit ctrl-d, how do I do that?

thank YOU

Re: ctrl-d in while statement

James R. Ferguson — Wed, 01 Mar 2006 16:20:28 GMT

Hi Gemini:

# while read LINE
> do
> echo "I read: ${LINE}"
> done

...to stop, use CTL_D.

Regards!

...JRF...

Re: ctrl-d in while statement

Gemini_2 — Wed, 01 Mar 2006 16:23:16 GMT

so easy, I complicated the problem.

thank YOU

Re: ctrl-d in while statement

Mark Greene_1 — Wed, 01 Mar 2006 16:34:15 GMT

This is not generally a good idea. Control-D is usually mapped to EOF; you can do stty -a to see this. Howevery, these values are all change able. For example, it's possible to map control-D to intr (which is usually a control-c) and then you'd have problems.

Having said that, you can do this:

char=""
while [[ $char -ne "^D" ]]
do
.
.
.
stty raw;char=`dd if=/dev/tty count=1 2>/dev/null`;stty -raw
done

and that may work for you.

mark

Re: ctrl-d in while statement

Jeff Schussele — Wed, 01 Mar 2006 16:46:22 GMT

Hi,

I agree with Mark.
Control chars can be problematic - especially for ttytype issues - even sessions themselves.
It's better to use standard alpha ASCII chars like "Q/q" for quit, "E/e" for exit, etc. Even whole words like quit or exit.
These are easily programable with case statements.

My $0.02,
Jeff

Re: ctrl-d in while statement

Bill Hassell — Wed, 01 Mar 2006 17:24:49 GMT

Another technique is to check that the line is empty (user just pressed CR), something like this:

while read LINE
do
if [ -z "$LINE" ]
then
echo "User entered nothing, exiting..."
exit
fi
...process other $LINE contents...
done

Be sure to quote "$LINE" to properly handle a null input.