Difference between bash-shell and ksh-shell by using while with read - what can I do in bash for the same response as in ksh?

Question

I have two scripts:

1. in bash

   #!/bin/bash
   H_VARIABLE=empty
   echo "Zeile1
         Zeile2" |
   while read satz
    do 
     H_VARIABLE="$H_VARIABLE $satz"
   done
   echo H_VARIABLE=$H_VARIABLE
   

   Result:

   H_VARIABLE=empty
   

2. in ksh

   #!/usr/bin/ksh
   H_VARIABLE=leer
   echo "Zeile1
         Zeile2" |
   while read satz
    do
     H_VARIABLE="$H_VARIABLE $satz"
   done
   echo H_VARIABLE=$H_VARIABLE
   

   Result:

   H_VARIABLE=leer Zeile1 Zeile2  
   

Conclusion: leer Zeile1 Zeile2 != leer

What can I do in bash to get the same response as in ksh?

Answer 1

The issue here is that, in bash, the while loop gets executed in a subshell when it is on the RHS of a pipe. You could do instead

H_VARIABLE=leer
while read satz
  do H_VARIABLE="$H_VARIABLE $satz"
done < <(
echo "Zeile1
      Zeile2"
)

using process substitution or, using a here string

H_VARIABLE=leer
while read satz
  do H_VARIABLE="$H_VARIABLE $satz"
done <<< "Zeile1
          Zeile2"

See also bash script var not changed after the loop