我下載了composer.phar，并mv到/usr/local/bin 目錄下。

macdeMacBook-Pro:bin mac$ mv ~/Downloads/composer.phar composer

macdeMacBook-Pro:bin mac$ chmod -R 755 composer

macdeMacBook-Pro:bin mac$ ls -al composer
-rwxr-xr-x@ 1 mac? staff? 1914314? 5 27 15:02 composer

macdeMacBook-Pro:bin mac$ composer

之后，一直是光標閃爍。沒有任何反應了。

問題解決了。
原來是php出了問題。重裝php就好了。