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Translated: How to Hide Linux Command Line History by Going Incognito (#4174)
* âFinish tranlating awk series part4 * Update Part 4 - How to Use Comparison Operators with Awk in Linux.md * translating: How to Hide Linux Command Line History by Going Incognito * finish translating How to Hide Linux Command Line History by Going Incognito * update translator
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How to Hide Linux Command Line History by Going Incognito
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If you’re a Linux command line user, you’ll agree that there are times when you do not want certain commands you run to be recorded in the command line history. There could be many reasons for this. For example, you’re at a certain position in your company, and you have some privileges that you don’t want others to abuse. Or, there are some critical commands that you don’t want to run accidentally while you’re browsing the history list.
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But is there a way to control what goes into the history list and what doesn’t? Or, in other words, can we turn on a web browser-like incognito mode in the Linux command line? The answer is yes, and there are many ways to achieve this, depending on what exactly you want. In this article we will discuss some of the popular solutions available.
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Note: all the commands presented in this article have been tested on Ubuntu.
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### Different ways available
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The first two ways we’ll describe here have already been covered in [one of our previous articles][1]. If you are already aware of them, you can skip over these. However, if you aren’t aware, you’re advised to go through them carefully.
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#### 1. Insert space before command
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Yes, you read it correctly. Insert a space in the beginning of a command, and it will be ignored by the shell, meaning the command won’t be recorded in history. However, there’s a dependency – the said solution will only work if the HISTCONTROL environment variable is set to “ignorespace” or “ignoreboth,” which is by default in most cases.
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So, a command like the following:
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```
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[space]echo "this is a top secret"
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```
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Won’t appear in the history if you’ve already done this command:
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```
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export HISTCONTROL = ignorespace
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```
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The below screenshot is an example of this behavior.
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The fourth “echo” command was not recorded in the history as it was run with a space in the beginning.
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#### 2. Disable the entire history for the current session
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If you want to disable the entire history for a session, you can easily do that by unsetting the HISTSIZE environment variable before you start with your command line work. To unset the variable run the following command:
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```
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export HISTFILE=0
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```
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HISTFILE is the number of lines (or commands) that can be stored in the history list for an ongoing bash session. By default, this variable has a set value – for example, 1000 in my case.
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So, the command mentioned above will set the environment variable’s value to zero, and consequently nothing will be stored in the history list until you close the terminal. Keep in mind that you’ll also not be able to see the previously run commands by pressing the up arrow key or running the history command.
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#### 3. Erase the entire history after you’re done
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This can be seen as an alternative to the solution mentioned in the previous section. The only difference is that in this case you run a command AFTER you’re done with all your work. Thh following is the command in question:
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```
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history -cw
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```
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As already mentioned, this will have the same effect as the HISTFILE solution mentioned above.
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#### 4. Turn off history only for the work you do
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While the solutions (2 and 3) described above do the trick, they erase the entire history, something which might be undesired in many situations. There might be cases in which you want to retain the history list up until the point you start your command line work. For situations like these you need to run the following command before starting with your work:
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```
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[space]set +o history
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```
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Note: [space] represents a blank space.
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The above command will disable the history temporarily, meaning whatever you do after running this command will not be recorded in history, although all the stuff executed prior to the above command will be there as it is in the history list.
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To re-enable the history, run the following command:
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```
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[Space]set -o history
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```
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This brings things back to normal again, meaning any command line work done after the above command will show up in the history.
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#### 5. Delete specific commands from history
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Now suppose the history list already contains some commands that you didn’t want to be recorded. What can be done in this case? It’s simple. You can go ahead and remove them. The following is how to accomplish this:
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```
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[space]history | grep "part of command you want to remove"
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```
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The above command will output a list of matching commands (that are there in the history list) with a number [num] preceding each of them.
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Once you’ve identified the command you want to remove, just run the following command to remove that particular entry from the history list:
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```
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history -d [num]
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```
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The following screenshot is an example of this.
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The second ‘echo’ command was removed successfully.
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Alternatively, you can just press the up arrow key to take a walk back through the history list, and once the command of your interest appears on the terminal, just press “Ctrl + U” to totally blank the line, effectively removing it from the list.
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### Conclusion
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There are multiple ways in which you can manipulate the Linux command line history to suit your needs. Keep in mind, however, that it’s usually not a good practice to hide or remove a command from history, although it’s also not wrong, per se, but you should be aware of what you’re doing and what effects it might have.
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via: https://www.maketecheasier.com/linux-command-line-history-incognito/?utm_medium=feed&utm_source=feedpress.me&utm_campaign=Feed%3A+maketecheasier
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作者：[Himanshu Arora][a]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://www.maketecheasier.com/author/himanshu/
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[1]: https://www.maketecheasier.com/command-line-history-linux/
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@ -0,0 +1,124 @@
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如何进入无痕模式进而隐藏 Linux 的命令行历史
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================================================================
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如果你是 Linux 命令行的用户，你会同意有的时候你不希望某些命令记录在你的命令行历史中。其中原因可能很多。例如，你在公司处于某个职位，你有一些不希望被其它人滥用的特权。亦或者有些特别重要的命令，你不希望在你浏览历史列表时误执行。
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然而，有方法可以控制哪些命令进入历史列表，哪些不进入吗？或者换句话说，我们在 Linux 终端中可以开启像浏览器一样的无痕模式吗？答案是肯定的，而且根据你想要的具体目标，有很多实现方法。在这篇文章中，我们将讨论一些行之有效的方法。
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注意：文中出现的所有命令都在 Ubuntu 下测试过。
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### 不同的可行方法
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前面两种方法已经在之前[一篇文章][1]中描述了。如果你已经了解，这部分可以略过。然而，如果你不了解，建议仔细阅读。
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#### 1. 在命令前插入空格
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是的，没看错。在命令前面插入空格，这条命令会被终端忽略，也就意味着它不会出现在历史记录中。但是这种方法有个前提，只有在你的环境变量 HISTCONTROL 设置为 "ignorespace" 或者 "ignoreboth" 才会起作用。在大多数情况下，这个是默认值。
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所以，像下面的命令：
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```
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[space]echo "this is a top secret"
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```
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你执行后，它不会出现在历史记录中。
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```
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export HISTCONTROL = ignorespace
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```
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下面的截图是这种方式的一个例子。
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第四个 "echo" 命令因为前面有空格，它没有被记录到历史中。
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#### 2. 禁用当前会话的所有历史记录
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如果你想禁用某个会话所有历史，你可以简单地在开始命令行工作前清除环境变量 HISTSIZE 的值。执行下面的命令来清除其值：
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```
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export HISTFILE=0
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```
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HISTFILE 表示对于 bash 会话其历史中可以保存命令的个数。默认情况，它设置了一个非零值，例如 在我的电脑上，它的值为 1000。
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所以上面所提到的命令将其值设置为 0，结果就是直到你关闭终端，没有东西会存储在历史记录中。记住同样你也不能通过按向上的箭头按键来执行之前的命令，也不能运行 history 命令。
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#### 3. 工作结束后清除整个历史
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这可以看作是前一部分所提方案的另外一种实现。唯一的区别是在你完成所有工作之后执行这个命令。下面是刚讨论的命令：
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```
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history -cw
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```
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刚才已经提到，这个和 HISTFILE 方法有相同效果。
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#### 4. 只针对你的工作关闭历史记录
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虽然前面描述的方法（2 和 3）可以实现目的，它们清除整个历史，在很多情况下，有些可能不是我们所期望的。有时候你可能想保存直到你开始命令行工作之间的历史记录。类似的需求需要在你开始工作前执行下述命令：
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```
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[space]set +o history
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```
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备注：[space] 表示空格。
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上面的命令会临时禁用历史功能，这意味着在这命令之后你执行的所有操作都不会记录到历史中，然而这个命令之前的所有东西都会原样记录在历史列表中。
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要重新开启历史功能，执行下面的命令：
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```
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[Space]set -o history
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```
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它将环境恢复原状，也就是你完成你的工作，执行上述命令之后的命令都会出现在历史中。
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#### 5. 从历史记录中删除指定的命令
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现在假设历史记录中有一些命令你不希望被记录。这种情况下我们怎么办？很简单。直接动手删除它们。通过下面的命令来删除：
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```
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[space]history | grep "part of command you want to remove"
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```
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上面的命令会输出历史记录中匹配的命令，每一条前面会有个数字。
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一旦你找到你想删除的命令，执行下面的命令，从历史记录中删除那个指定的项：
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```
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history -d [num]
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```
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下面是这个例子的截图。
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第二个 ‘echo’命令被成功的删除了。
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同样的，你可以使用向上的箭头一直往回翻看历史记录。当你发现你感兴趣的命令出现在终端上时，按下 “Ctrl + U”清除整行，也会从历史记录中删除它。
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### 总结
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有多种不同的方法可以操作 Linux 命令行历史来满足你的需求。然而请记住，从历史中隐藏或者删除命令通常不是一个好习惯，尽管本质上这并没有错。但是你必须知道你在做什么，以及可能产生的后果。
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via: https://www.maketecheasier.com/linux-command-line-history-incognito/?utm_medium=feed&utm_source=feedpress.me&utm_campaign=Feed%3A+maketecheasier
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作者：[Himanshu Arora][a]
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译者：[chunyang-wen](https://github.com/chunyang-wen)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://www.maketecheasier.com/author/himanshu/
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[1]: https://www.maketecheasier.com/command-line-history-linux/
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