How to use for/while loop with multiple variables?

Shell Programming and Scripting
1

Hi,

I have two variables like below which will always be of the same size
a=1:2:3
b=A:B:C

I need to use a for/while loop that will have both the variables available. I cannot use an array here and will probably might iterate through the variable as echo $a | tr ':' '\n' and thus iterate through the variables one by one. I am doing the below

 
for i in `echo $a | tr ':' '\n'`
do
  echo "the variable is $i"
done

But I want to traverse both the lists at the same time. So for eg if I have the first element in list 1, I should also have the first element in list 2. I could have done this with a count variable, but wanted to see if there is another easy way

2

You don't need backticks and tr, the shell's own built-in splitting will suffice.

How about this?

OLDIFS="$IFS"
IFS=":"

set -- $a # Sets $1 $2 ...  parameters to 1 2 ...

for x in $b
do
        echo $x $1
        shift # Removes first parameter, so 1 2 ... becomes 2 ...
done

IFS="$OLDIFS"
2 Likes
3

Thanks a bunch for the quick response. Is there a way you can help me with this using the same format , like the "echo" and "trim". The codereview people will ask for consistency and all our coding has been done previously in this fomat. So I was trying to get something in the same format

4

If the code review people expect your code to remain overblown and bugprone because all your code before was too, both you and your reviewers have a big problem...

You have everything you need to do this yourself if you insist on doing so. Remove all the IFS stuff, and anywhere you see a simple easy $a and $b, slap in one of your big echo | tr kludges.

5

In case it's an oversight, be aware that command substitution strips all trailing newlines. If there are empty fields at the end of $a, they will be lost.

Regards,
Alister

6

All bash:

while IFS=: read i && IFS=: read j<&3
do
  printf "%s\n" "$i, $j"
done <<<"${a//:/$'\n'}" 3<<<"${b//:/$'\n'}"