Splitting a file in a shell script adds unwanted newlines - zsh

Question

I need to process a long text file splitting it into many smaller files. I have a single pass while - read - done <inputfile loop and when a line is matched, that signals the start of new output file. The matched lines are always preceded by a newline character in the input file.
My problem is that the output files (except the final one) are extended by a newline character. I have recreated the problem in this short example.
#!/bin/zsh
rm inputfile outputfile1 outputfile2
IFS=''
printf "section1\nsection1end\n\nsection2\nsection2end\n" >inputfile
echo " open outputfile1"
exec 3<> outputfile1
counter=1
IFS=$'\n'
while IFS= read line; do
if [[ "$line" == "section2" ]]; then
echo " Matched start of section2. Close outputfile1 and open outputfile2"
exec 3>&-
exec 3<> outputfile2
fi
echo "$line" >&3
echo $counter $line
let "counter = $counter + 1"
done <inputfile
echo " Close outputfile2"
exec 3>&-
echo
unset IFS
echo `wc -l inputfile`
echo `wc -l outputfile1`
echo `wc -l outputfile2`
echo " The above should show 5, 2, 2 as desired number of newlines in these files."
Which outputs:
open outputfile1
1 section1
2 section1end
3
Matched start of section2. Close outputfile1 and open outputfile2
4 section2
5 section2end
Close outputfile2
5 inputfile
3 outputfile1
2 outputfile2
The above should show 5, 2, 2 as desired number of newlines in these files.

Answer 1

Option 1
Get rid of all empty lines. This only works if you don't need to retain any of the empty lines in the middle of a section.
Change:
echo "$line" >&3
To:
[[ -n "$line" ]] && echo "$line" >&3
Option 2
Rewrite each file using command substitution to trim any trailing newlines. Works best with short files. Change:
exec 3>&-
exec 3<> outputfile2
To:
exec 3>&-
data=$(<outputfile1)
echo "$data" >outputfile1
exec 3<> outputfile2
Option 3
Have the loop write the line from the prior iteration, and then do not write the final line from the prior file when you start a new file:
#!/bin/zsh
rm inputfile outputfile1 outputfile2
IFS=''
printf "section1\nsection1end\n\nsection2\nsection2end\n" >inputfile
echo " open outputfile1"
exec 3<> outputfile1
counter=1
IFS=$'\n'
priorLine=MARKER
while IFS= read line; do
if [[ "$line" == "section2" ]]; then
echo " Matched start of section2. Close outputfile1 and open outputfile2"
exec 3>&-
exec 3<> outputfile2
elif [[ "$priorLine" != MARKER ]]; then
echo "$priorLine" >&3
fi
echo $counter $line
let "counter = $counter + 1"
priorLine="$line"
done <inputfile
echo "$priorLine" >&3
echo " Close outputfile2"
exec 3>&-
echo
unset IFS
echo `wc -l inputfile`
echo `wc -l outputfile1`
echo `wc -l outputfile2`
echo " The above should show 5, 2, 2 as desired number of newlines in these files."