Shell Programming and Scripting

Hi all,

I am running AIX version 4. I have a shell script that is calling another script. I want the called script to obtain a value and pass it back to the calling script. So far, I know that to pass a parameter to a called script is as such:

sh proc2.sh $1 $2 etc.

What I don't know how to do though is pass a parameter back the other way. Can any one help??

Thanks
Jules

sh proc2.sh $1 $2 etc

is really off to a bad start. It would be better to call it proc2 rather than proc2.sh. And invoking it via an explicit call to sh is a very bad idea. You should make the first line of proc2 something like:
#! /usr/bin/sh
(but use your path to sh) and then do a:
chmod +x proc2
When you do these things you can then run proc2 as an executable:
proc2 $1 $2

Now if the author of proc2 decides to rewrite it in c or ksh or perl etc, you don't need to change every script that called it. Famous unix program like "touch" and "grep" started out as sh scripts.

Also $1 and $2 refer to the first and second positional parameters in the caller. It would be rare to pass those to a second program.

Since you're using sh rather than ksh, you must be using expr for any arithmetic like this:
x=1
x=`expr $x + 1`
This is one way to return a parameter. The backticks take the stdout from the program. And the other way it the exit code, which is very limited.

Here is a sample:
#! /usr/bin/sh
echo hello
exit 2

And another script would do this:
x=`sample`
echo $x
sample
echo $?

You can use the exit command to pass back an error number. e.g. exit 56

This value is passed back into the calling shell and can be examined in the built in variable $?.

If you want to do something a little more complex (like a string) then the called script should echo the return value e.g.

echo $SOME_VARIABLE.

To use this value in the calling script:

RETURN_VAR=`called_script param1 10 20`

Notice the back quote(`). You are telling ksh to replace the results of the script into the variable i.e. what ever is echoed to stdout.

You could also use syntax like:

RETURN_VAR=$(called_script param1 10 20)

If you want to pass back several parameters then echo them as one string, using a delimiter to separate the values.

I called the script like you said in the funny `` quotes. In the called program did the echo...all worked like a charm.

Thanks MBB for that extra bit at the end, my very next question was in fact; "What about when you have more than 1 parameter"!

Appreciate the help guys, thanks.

how about this one

echo $retval|awk -v x="YOUR OUTPUT" '{print substr(x,2,4)}'

so you return the output of ur script using

retval=`your script`

and use retval as a variable to awk and the use the substring function of awk to split the output

i know echo retval doesnt look elegant tho, but this is just a sample to hint you the use of awk and its substr function

probably

if retval is 2 4 5 6
echo $retval|awk '{print substr($0,2,4)'

this would result into " 4 6"

Thanks for the reply LP. I must admit, I know nothing about AWK. I have tried once or twice to use it, all I get are strange errors that I can't debug. My UNIX administrator don't even know how the command works. They gave me a book once that should have explained the awk procedure, but it was a piece of rubbish - couldn't make head or tails of it.

I would love to be able to use the awk procecedure cos I understand that its really powerfull. Where do I go though to get a really good set of definitions of the syntax? Looking at your code I can understand what you are getting at, but I don't know the mechanics of what you are doing, e.g. what is the -v option and what other type of options are there, why do you print the results etc etc etc