Description of problem:
shell commands seem to not work properly in specfiles.

In bash if you do:
echo 1.4.2 | sed 's/.*\.//'
it will correctly reply:
2

but in a specfile, if you do:
%define minor %(echo 1.4.2 | sed 's/.*\.//')
it returns an empty string.

Version-Release number of selected component (if applicable):
4.3.1

How reproducible:
Always

Steps to Reproduce:
1. write a specfile
2. run a shell command containing an operation on regular expressions
while defining a macro
3. it returns the wrong value
  
Actual results:
on some operations it returns the wrong value

Expected results:
to work properly

Additional info: