UNIX for Dummies Questions & Answers

I have a while read loop that reads values inside of a file and then performs an expr operation on each.

Everything works fine, the way it's supposed to but, once the loop is finished, I can not access the variable that I used inside of the loop (but that variable was created outside of the loop).

In other words...

The output of that last echo is "myVar:0"
Is this something I'm not allowed to do? I changed the value of the variable I created outside of the loop, from within the loop, but it didn't change after the loop was done, outside.

I tested the loop, and yes, the loop works, the values are there.
Should I just redirect the output to a file and just use the file as my variable?

shell != perl
loose the $ sign: varInLoop=... #This carries an integer

Code:

#!/bin/ksh

myVar=0

while read LINE
do
  myVar=`expr $myVar + 1`
done < myFile.txt

echo "myVar->[${myVar}]"

You'll also find that...

Code:

while read line; do
  foo="bar"
done < some.txt
echo $foo

will echo bar, whereas

Code:

echo "one line" | while read line; do
  foo="bar"
done
echo $foo

will *not* echo bar.... hence the variable cannot be "exported"....

the latter example's while loop is executed in a subshell.

This holds true for bash and pdksh, at least on the system I have access to at the moment....

Cheers
ZB

thanks to both..

The main fault was..

Instead of #!/bin/ksh
I put #!/bin/sh

Is there some kind of reference page somewhere that tells me the differences between sh and ksh, because I had no Idea that I couldn't do this "variable exporting" with sh.

Just as a note, if you're using a "proper" (i.e. non-Public Domain) Korn Shell, then even piping to a while loop results in the variable being set as you'd like it to be set (even though the pipe should mean that the while is executed in a subshell so the variable *shouldn't really be set* - surely this therefore isn't POSIX compliant?!)....

Code:

$ what `which ksh`
/usr/bin/ksh:
        Version M-11/16/88i
        SunOS 5.8 Generic 110662-15 Jun 2004
$ echo "one line" | while read line; do       
>   foo=bar                                
> done
$ echo $foo
bar

Consistency, that's what we like to see

Cheers
ZB

that's good to know.
this forum is becoming my unix bible, i have book marks everywhere for reference.. this one's definitely being marked.

I'd like to check to see if a variable is empty
If it is empty, then I'd like to set it to zero.
But I'm getting the syntax wrong.

Should I, or can I, use if [ $myVar -lt 1 ]; ?

I get a get_clientkpi.sh[80]: test: argument expected for that if statement above.

If you're using ksh or bash, use the
${varname:=default} construct, e.g.

Code:

$ myVar=20
$ myVar=${myVar:=0}
$ echo $myVar
20
$ unset myVar
$ echo $myVar

$ myVar=${myVar:=0}
$ echo $myVar
0

Cheers
ZB