$ cat asdf
#!/bin/sh
echo "line 1"
echo "line 2"
echo "line 3" >&2
echo "line 4" >&2

$ perl -le'$x=`./asdf 2>&1`; print "<<Captured $x>>"'
<<Captured line 1
line 2
line 3
line 4
>>

##</code><code>##

$ perl -e'print "Captured $_" for `./asdf 2>&1`;'
Captured line 1
Captured line 2
Captured line 3
Captured line 4