Shell Programming and Scripting

PTL,
Skrynesaver and Corona688 both identified one third of your problems. (At least I assume that there is no command named invalid on your system.) You need to combine their suggestions to get rid of the problems they identified in your original script. Try:

Code:

while 1
do
        printf 'Enter  L(Load id), M(Mark id), or E(Exit): '
        read answer
        case "$answer" in
                (E) break;;
                (L) load_id.sh;;
                (M) mark_id.sh;;
                (*) echo 'Invalid choice, try again' >&2
        esac
done

And, I made a few other minor changes:I hope this helps.

Wow!!! Thank you all again! I hadn't realised there were responses waiting for me, I was busy trying various other options.

You were all correct i.e. bits from each suggestion put together seem to have given me what I wanted. I used a while loop and I took out the 'exec' from the called script. The modification I had made before was to replace the exec with '.' which apparently was doing the same as 'exec' and hence no good. So what I have now done is to call the load_id.sh etc without 'exec' or '.'

thanks again. Hopefully that should be it.

PTL

It does something very different, actually.

With exec, the running program that calls the other script ceases to exist... There is nothing left to return to.

With ., your shell still exists, but a new one is not made... The new script is run literally inside the old as if the code had been typed right inside it. When it hits exit, it kills your shell.

When you run it without exec or . it creates a whole new shell to run it in, which dies without killing your original one.

Since you didn't post your code, I never guessed what you did. Please always post your code.

Hi Don,
The point you made about portability of "\c" is interesting. How do I get the cursor to go on to the next line i.e. what is the replacement for "\c" when I use printf?
I have indeed noticed that "\c" on our systeem, while it moves the cursor to the next line (which I want), displays itself as well which I don't really want.

thanks
PTL

By convention, when you print a prompt, you should leave the cursor at the end of the prompt and let the user's response provide the trailing newline character that will move the cursor to the next line.

On UNIX Systems, echo recognizes several backslash escapes including:
\a alert (screen flash or bell character or both)
\b backspace character
\f form feed character
\t tab character
\n newline character
\c stop looking for more text and skip trailing newline
and accepts no options. Any arguments starting with a - will be printed as is.

On BSD Systems, echo does not treat backslash as special, but has a -n option that will skip the trailing newline. Any other operands that look like options will be printed as is.

The standards allow either the BSD or the UNIX System behavior.

On Linux Systems, echo provides several options that are not allowed by the standards. Some of them recognize backslash escapes; some of them don't. Some of them skip the trailing newline; some don't.

Given the command:

Code:

echo -n -x -- "a\tb: \c"

A UNIX System (except OS X) will produce:

Code:

-n -x -- a	b: >>>Cursor here<<<

while a BSD System will produce:

Code:

-x -- a\tb: \c>>>Cursor here<<<

and a Linux System will do something different from either of the above.
A bug in OS X (which is supposed to be a UNIX System) prints the \t instead of replacing it with a tab.

As has been said many times in these forums before, if any of the operands to echo start with a minus sign or contain a backslash character, use printf instead of echo if you want to write a portable script.

PS The format operand to printf recognizes all of the normal C printf() backslash escapes. So, \n in the format string prints a newline.