Install bash:

opkg update
opkg install bash
nano /www/cgi-bin/test.sh
#!/bin/bash
echo "Content-type: text/html"
echo 
echo "<html><head><title>hello world</title></head><body><p>It works!</p></body>"
exit 0
chmod 755 /www/cgi-bin/test.sh

View result at "http://192.168.0.102/cgi-bin/test.sh"

It works!