在shell脚本里怎么判断某命令存不存在

在shell中怎么判断某命令存不存在?一开始想着用which，但发现不好使。。。正确的使用方式，应如下：

hash go 2> /dev/null || { echo >&2 "go sdk没有安装..."; exit 1; }

在网上查到的，例子：

$ command -v foo >/dev/null 2>&1 || { echo >&2 "I require foo but it's not installed.  Aborting."; exit 1; }
$ type foo >/dev/null 2>&1 || { echo >&2 "I require foo but it's not installed.  Aborting."; exit 1; }
$ hash foo 2>/dev/null || { echo >&2 "I require foo but it's not installed.  Aborting."; exit 1; }

参考：
https://www.cnblogs.com/embedded-linux/p/6206064.html
原文链接：
https://stackoverflow.com/questions/592620/how-can-i-check-if-a-program-exists-from-a-bash-script/677212#677212