Eu suponho que você deseja executar:
wget http://mywebsite.com/teste?id=codigo1&x=&date=01/01/2017" --load-cookies=cookies.txt
wget http://mywebsite.com/teste?id=codigo1&x=&date=02/01/2017" --load-cookies=cookies.txt
wget http://mywebsite.com/teste?id=codigo1&x=&date=03/01/2017" --load-cookies=cookies.txt
wget http://mywebsite.com/teste?id=codigo2&x=&date=01/01/2017" --load-cookies=cookies.txt
wget http://mywebsite.com/teste?id=codigo2&x=&date=02/01/2017" --load-cookies=cookies.txt
wget http://mywebsite.com/teste?id=codigo2&x=&date=03/01/2017" --load-cookies=cookies.txt
se o arquivo codigos.txt
contiver:
codigo1
codigo2
e dates.txt
contém:
01/01/2017
02/01/2017
03/01/2017
então isso funcionará:
mywget() {
wget "http://mywebsite.com/teste?id=$1&x=&date=$2" --load-cookies=cookies.txt;
}
export -f mywget
parallel mywget :::: codigos.txt dates.txt