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"read -p"是什么意思?在Linux Shell脚本中做什么?

分类: 技术问答 • 2022-06-11 23:54:58
问题描述：

我有一个已复制和编辑的脚本.如果可能的话，我需要解释几行.

I have a script that I have copied and edited. There are a couple of lines in there that I need explaining if possible please.

以下是这些行:

     read -p "please enter the username you wish to create: " username
     if id -u $username >/dev/null 2>&1; then

read -p的作用是什么? id -u的作用是什么? >/dev/null 2&1;的作用是什么? 然后在脚本中继续，它的这一行内容如下:

What does read -p do? What does id -u do? What does >/dev/null 2&1; do? Then further on in the script, it has this line that says this:

     sudo useradd -g $group -s $bash -d $homedir -m $username -p $password

再次请有人解释这行中的所有减号吗? (-g，-s，-d，-m，-p)

Again please could someone explain all the minus signs in this line please? (-g, -s, -d, -m, -p)

答

首先，结构<command> -<option>表示您要使用与<option>相对应的选项执行<command>.命令后的-表示以下字母是一个选项.大多数命令都有几个可以使用的选项.选项通常使用单个字母或几个用-分隔的单词来定义.

First off, the structure <command> -<option> means that you want to execute <command> using the option corresponding to <option>. A - after a command means that the following letter is an option. Most commands have several options you can use. Options are usually defined using either a single letter or a couple of words separated by -.

旁注:对于包含几个单词而不是单个字母的选项，通常会使用两个减号--而不是一个，表示它是长命名"选项.

Side Note: For options that are a couple of words rather than a single letter, often it will use two minus signs -- instead of one, signifying that it is a "long named" option.

因此，使用read -p示例，这意味着您想使用p选项执行read，该选项代表提示.

So, using the read -p example, this means you want to execute read using the p option, which stands for prompt.

现在，有时选项将需要一个参数.在您的示例中，useradd的选项具有参数.参数的定义通常类似于<command> -<option> [argument].因此，在useradd示例中，$group是选项g的参数.

Now, sometimes an option will require an argument. In your examples, the options to useradd have arguments. Arguments are usually defined like <command> -<option> [argument]. So, in the useradd example, $group is an argument for the option g.

现在输入命令本身:

read 是一个内置的bash(不是POSIX shell命令)，它读取来自标准输入.

read is a bash built-in (not a POSIX shell command) that reads from standard input.

  • -p选项使它作为提示阅读，这意味着它在尝试读取输入之前不会添加尾随换行符.
  • The -p option makes it read as a prompt, meaning it doesn't add a trailing newline before trying to read input.

if 检查测试的返回状态命令(在本例中为id -u $username >/dev/null 2>&1)

  • 如果返回状态为0，则执行then部分

id 打印用户组和ID

id prints user groups and ids

  • -u选项仅打印有效的用户ID".
  • >/dev/null 2>&1 将标准输入和标准错误重定向到/dev/null，这意味着它们不会打印到终端上.
  • The -u option "prints only the effective user ID".
  • >/dev/null 2>&1 redirects standard input and standard error to /dev/null, meaning they do not get printed to the terminal.

useradd 创建一个新用户

useradd creates a new user

  • -g为用户设置初始组
  • -s设置用户登录shell的名称
  • -d设置用户登录目录的名称
  • -m表示要创建用户的主目录(如果该目录不存在).
  • -p定义用户的加密密码.
  • -g sets the initial group for the user
  • -s sets the name of the user's login shell
  • -d sets the name of the user's login directory
  • -m says to create the user's home directory if it does not exist.
  • -p defines the user's encrypted password.

供以后参考，您可以通过在命令行上执行man <command>在linux手册页中查找命令.这些手册页告诉您命令的功能，并说明命令的所有选项.

For future reference, you can look up commands in the linux manual pages by doing man <command> on the command line. These manual pages tell you what a command does, as well as explaining all of its options.

像read这样的Bash内置控件都位于单个手册页上，这不是最容易使用的东西.对于那些我来说，搜索它们比较容易.通常，结果中会出现 http://ss64.com/，其中包含来自bash内置函数的信息手册页，但通过命令分为不同的页面.我发现这更容易使用.

Bash built-ins like read are all on a single man page that is not the easiest thing to use. For those I find googling them easier. Usually http://ss64.com/ will come up in the results, which contains the info from the bash built-ins man page, but separated into different pages by command. I find this much easier to use.

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