from：https://blog.csdn.net/u011068702/article/details/80787824
command [-pVv] command [arg ...]
Run command with args suppressing the normal shell function lookup. Only builtin commands or commands found in the PATH are executed.
If the -p option is given, the search for command is performed using a default value for PATH that is guaranteed to find all of the standard utilities.
If either the -V or -v option is supplied, a description of command is printed. The -v option causes a single word indicating the command or filename used to invoke command to be displayed; the -V option produces a more verbose description.
If the -V or -v option is supplied, the exit status is 0 if command was found, and 1 if not. If neither option is supplied and an error occurred or command cannot be found, the exit status is 127.
Otherwise, the exit status of the command builtin is the exit status of command.
1、command解釋
command命令在shell腳本里面，如果發現有個函數和我們需要執行的命令同名，我們可以用command用來強制執行命令，而不是同名函數，然後我們也可以在shell腳本里面判斷某個命令是否存在，我們平時一般用which命令也行。
2、測試代碼
#!/bin/bash
function pwd()
{
echo "I am pwd function"
}
echo "shell run pwd"
pwd
echo "shell command pwd"
command pwd
if command -v pwd > /dev/null; then
echo "pwd command has found"
else
echo "pwd command has not found"
fi
if command -v pwd1 > /dev/null; then
echo "pwd1 command has found"
else
echo "pwd1 command has not found"
fi
3、運行結果
./command
shell run pwd
I am pwd function
shell command pwd
/home/chenyu/Desktop/linux/dabian/python
pwd command has found
pwd1 command has not found