#!/bin/bash

x=1
echo fred>junk ; while read var ; do x=55 ; done <junk
echo x=$x
#    x=55 .. I'd expect this result

x=1
cat junk | while read var ; do x=55 ; done
echo x=$x
#    x=1 .. but why?

x=1
echo fred | while read var ; do x=55 ; done
echo x=$x
#    x=1  .. but why?

a=0; a=1 | a=2; echo $a

cat junk | {
  while read var ; do x=55 ; done
  echo x=$x
}