Why does an ampersand in URL cause failure of the following command? I want to open a web page by running Safari in Terminal, placing the URL as an argument. This works as expected: open -a safari "http://endic.naver.com/search.nhn?sLn=en&searchOption=all&query=good" But once the quotes being removed, it wouldn't work as expected: open -a safari http://endic.naver.com/search.nhn?sLn=en&searchOption=all&query=good Instead, it returns: [3] 5395 [4] 5396 [1] Done open -a safari http://endic.naver.com/search.nhn?sLn=en [2] Done searchOption=all Seems like ampersand in the URL was treated as "running previous command in the background", though there is no space following the ampersand in the URL.