Change directory for saving a file and return to old directory - bash

Question

I wrote a very little and basic script which compares two files and writes all matching lines into a file.
I now want to secure, that no matter from which directory/working directory you run the bash script, the file is stored in the directory where the script is located.
#! /bin/bash
typeset -i count=1
typeset -i useable_counter=1
file="Fundstellen.txt"
curDir=`pwd`
wantedDir="/Users/Stephan/Documents/Schule/SYT/Skripting/bin/Uebungen"
echo `pushd ${wantedDir}`
if [ -e $file ]; then
echo `chmod 777 ${file}`
echo `rm ${file}`
fi
echo `touch ${file}`
while read pass; do
pass_nr=`echo $pass | cut -d ":" -f 3`
while read groups; do
group_nr=`echo $groups | cut -d ":" -f 3`
if [ "$pass_nr" = "$group_nr" ]; then
if [ $count -gt 15 ]; then
echo "#$useable_counter: $pass in $groups" >> $file
useable_counter=$useable_counter+1
fi
count=$count+1
fi
done < /etc/group
done < /etc/passwd
echo `chmod 444 $file`
echo `popd`
echo "Writing done!"
That's my script with the pushd command to get to the directory in which the script is located and popd should return.
But still, the output file is created in the directory/working directory, from where the script is launched.
What do I have to change so it'll work? I already tried to use normal cd to change the directory, that's why the variable curDir stores the starting directory.

Answer 1

By putting pushd into backticks, you're running it in a subshell. No subshell can change the current working directory of its parent shell.
Just call
pushd "$wantedDir"
directly, and same with popd.

Answer 2

Your script is a hopeless mess. All you need to produce output in the named file is
command >/Users/Stephan/Documents/Schule/SYT/Skripting/bin/Uebungen/Fundstellen.txt
Generally, very few scripts need to explicitly cd and fewer still would need to pushd and popd -- these commands are almost exclusively for interactive use.
The loop where you read all of the group file for every entry in the passwd file is extremely inefficient, especially when the purpose of the inner loop seems to be to find only a small subset of the records in the file. Very often, when you see while read, you want Awk instead. Here is a simple framework for doing that.
awk -F : 'NR==FNR { ++p[$3]; next }
FNR > 15 && $3 in p { print "#" ++i ": " $3 " in " $0 }' /etc/passdwd /etc/group
It's not clear what the 15 is supposed to accomplish. Is it a bug in your script, or is the intent to only skip the first 15 lines on the first iteration?