1. 命令解析
命令用途：
显示命令的全部路径到标准输出。
命令格式：
which [options] [--] COMMAND [...]
命令参数：
--version, -[vV] Print version and exit successfully.
--help, Print this help and exit successfully.
--skip-dot Skip directories in PATH that start with a dot.
--skip-tilde Skip directories in PATH that start with a tilde.
--show-dot Don't expand a dot to current directory in output.
--show-tilde Output a tilde for HOME directory for non-root.
--tty-only Stop processing options on the right if not on tty.
--all, -a Print all matches in PATH, not just the first
--read-alias, -i Read list of aliases from stdin.
--skip-alias Ignore option --read-alias; don't read stdin.
--read-functions Read shell functions from stdin.
--skip-functions Ignore option --read-functions; don't read stdin.
2. 示例
2.1 显示ls命令的路径
[root@test headTest]# which ls
alias ls='ls --color=auto'
/usr/bin/ls
