Behavior of variable creation inside bash function

Question

I am using the function below to increment an outside script. The main purpose of this is just to return some data from ifconfig and ping test outputs. I am trying to set them inside the same function using variables, just to do some other "pipes" and concactenate them again with other information. But I got this behavior. Basically, what I am trying to do is:

    > for i in $(ifconfig | grep "inet addr" | tr -s " " | cut -d" " -f 3 | cut -d: -f2) ; do ping -c1 $i | grep packet | a=`echo $i-$(cut -d,
    -f3)` | echo $a; done  
4  
4  
4  
4

As you can see, it returns the number 4 for each iteration.

If I just remove the variable attribution, I get the output I was expecting to set in variable 'a' at first place:

> for i in $(ifconfig | grep "inet addr" | tr -s " " | cut -d" " -f 3 | cut -d: -f2) ; do ping -c1 $i | grep packet | echo $i-$(cut -d, -f3); done
10.0.2.15- 0% packet loss
192.168.0.2- 0% packet loss
10.0.2.100- 0% packet loss
127.0.0.1- 0% packet loss

• Why am I getting number 4 as output in first function code execution?
• How can I set a variable inside the same function and echo it again after some pipelines? Is that possible?

Best regards !

Answer 1

 for i in $(...) ; do ... | a=`...` | echo $a; done

Why am I getting number 4 as output in first function code execution?

Because a=`...` and echo $a are executed in different subshells / subprocesses. a=1; a=3 | echo $a will print 1 in any shell. There's no way to pass a variable from a subshell to its parent.

How can I set a variable inside the same function and echo it again after some pipelines? Is that possible?

No. Unless you set it in the main script, before the pipeline.

Answer 2

If you restructure the last part of the pipeline using sed I think you can get what you want. The sed script matches the whole standard input and replaces it with the value of $i followed by - and the third field of your ping output (from stdin). For example,

$ for i in $(ifconfig | grep "inet addr" | tr -s " " | cut -d" " -f3 | cut -d: -f2); do \
    ping -c1 $i | grep packet | cut -d, -f3 | sed "s/\(.*\)/$i - \\1/"; \
done
123.145.167.189 -  0% packet loss
127.0.0.1 -  0% packet loss