@Ravstar
Thinking about it, even if the OS is pretty old, it should have the TAR command available.
Try changing the gzip/gunzip line to the following:-
tar -xzvf /media/hdd/epg/filename.xml.gz
wget -O /media/hdd/epg1/epg_ripper_IN2.xml.gz https://url
gunzip -f /media/hdd/epg1/epg_ripper_IN2.xml.gz
sed -i 's/+0530/+0000/g' /media/hdd/epg1/epg_ripper_IN2.xml
mv /media/hdd/epg1/epg_ripper_IN2.xml /media/hdd/epg
rm /media/hdd/epg1/epg_ripper_IN2.xml.gz
I have tried replacing it to gzip -d and tar -xzvf none of them worked either