Linux clear terminal history

История команд Linux

В терминале Linux, кроме всего прочего, есть одна замечательная вещь. Это история команд Linux. Все команды, которые вы вводите во время работы сохраняются и вы можете найти и посмотреть их в любой момент. Также можете вернуться на несколько команд чтобы не набирать недавно выполненную команду заново.

В этой небольшой статье мы рассмотрим как пользоваться историей команд Linux, как ее настроить, а также рассмотрим полезные приемы, которые могут помочь вам в работе.

История команд Linux

Большинство задач, связанных с историей команд, мы будем выполнять либо с помощью команды history, либо с помощью оболочки. В истории хранится последняя 1000 команд, которые вы выполняли. Чтобы посмотреть всю историю для этого терминала просто запустите команду history без параметров:

Для дополнительных действий с историей вам могут понадобиться опции. Команда history linux имеет очень простой синтаксис:

$ history опции файл

В качестве файла можно указать файл истории. По умолчанию история для текущего пользователя хранится в файле

/.history, но вы можете задать, например, файл другого пользователя. А теперь рассмотрим опции:

• -c — очистить историю;
• -d — удалить определенную строку из истории;
• -a — добавить новую команду в историю;
• -n — скопировать команды из файла истории в текущий список;
• -w — перезаписать содержимое одного файла истории в другой, заменяя повторяющиеся вхождения.

Наиболее полезной для нас из всего этого будет опция -c, которая позволяет очистить историю команд linux:

Так вы можете посмотреть только последние 10 команд:

А с помощью опции -d удалить ненужное, например, удалить команду под номером 1007:

Если вы хотите выполнить поиск по истории bash, можно использовать фильтр grep. Например, найдем все команды zypper:

history | grep zypper

На самом деле работать с историей еще более просто с помощью оболочки, возможно, вы уже используете многие ее функции, но о некоторых точно не знаете. Рассмотрим их:

Чтобы показать предыдущую команду просто нажмите стрелку вверх, так можно просмотреть список раньше выполненных команд.

Вы можете выполнить последнюю команду просто набрав «!!». Также можно выполнить одну из предыдущих команд указав ее номер «!-2»

Чтобы выполнить поиск по истории прямо во время ввода нажмите Ctrl+R и начните вводить начало команды.

Если вы знаете, что нужная команда была последней, которая начиналась на определенные символы, например, l, то вы можете ее выполнить, дописав «!l»:

Если нужная команда последняя содержала определенное слово, например, tmp, то вы можете ее найти, использовав «!?tmp»:

Если вы не хотите, чтобы выполняемая команда сохранилась в истории просто поставьте перед ней пробел.

Таким образом, вы можете очень быстро отыскать нужную команду, если помните как она была написана. История команд bash хранит очень много команд и этого вполне достаточно для комфортной работы.

Настройка истории Linux

Linux — очень настраиваемая и гибкая система, поэтому настроить здесь можно все, в том числе и историю. По умолчанию выводится только номер команды, но вы можете выводить и ее дату. Для этого нужно экспортировать переменную HISTORYFORMAT вместе нужным форматом:

export HISTTIMEFORMAT=’%F %T ‘
$ history

Для форматирования можно использовать такие модификаторы:

• %d – день;
• %m – месяц;
• %y – год;
• %T – штамп времени;
• %F — штамп даты.

Вы можете указать какие команды не стоит отображать, например, не будем выводить ls -l, pwd и date:

export HISTIGNORE=’ls -l:pwd:date:’

Также можно отключить вывод одинаковых команд:

Существует два флага, ignoredups и ignorespace. Второй указывает, что нужно игнорировать команды, начинающиеся с пробела. Если вы хотите установить оба значения, используйте флаг ignoreboth. Используйте переменную HISTSIZE, чтобы установить размер истории:

По умолчанию история сохраняется для каждого терминала отдельно. Но если вы хотите чтобы все ваши команды немедленно синхронизировались между всеми терминалами, то это очень просто настроить. Добавьте такую переменную:

export PROMPT_COMMAND=»$history -a; history -c; history -r;»

Для тестирования работы вы можете набирать эти команды прямо в терминале и сразу видеть результат, но для сохранения добавьте нужные строки в ваш

export PROMPT_COMMAND=»$history -a; history -c; history -r;»
$ export HISTCONTROL=ignoredups
$ export HISTTIMEFORMAT=’%F %T ‘

Готово, теперь осталось сохранить изменения и перезапустить ваши терминалы. Теперь ваша история будет выводить дату, игнорировать дубли и синхронизироваться между терминалами.

Выводы

В этой статье мы рассмотрели что такое история команд linux, как с ней работать, как применяется команда history linux и какие настройки можно использовать для более комфортной работы. Если у вас остались вопросы, спрашивайте в комментариях!

Источник

How to Clear BASH Command Line History in Linux

The bash history keeps a record of all commands executed by a user on the Linux command line. This allows you to easily run previously executed commands by using the “up arrow” or “down arrow” keys to scroll through the command history file.

In this article, we will show you two simple ways to clear your command-line history on a Linux system.

The major reason for removing command-line history from the Linux terminal is to prevent another user, who could be using the same account.

For instance if you have typed a command that contained a password in plain-text and you don’t want another system user or an attacker to see this password, you need to delete or clear the history file.

Take a look at the command below, here the user aaronkilik has typed the database server password on the command line.

If you look into th bash history file towards the end, you will see the password typed above in there.

Check Last Executed Commands

The bash_history file is normally located in a user’s home directory /home/username/.bash_history.

To remove a single line from the history file, use the -d option. For example, if you want to clear a command where you entered clear-text password as in the scenario above, find the line number in the history file and run this command.

To delete or clear all the entries from bash history, use the history command below with the -c option.

Alternatively, you can use the command below to delete history of all last executed commands permanently in the file.

Note: A normal user can only view his/her own command history, but the root user can view the command history of all other users on the system.

You can learn more about the bash history file and useful history commands here: The Power of Linux “History Command” in Bash Shell.

Always remember that all commands you run are recorded in a history file, so do not type plain-text passwords on the command line. If you have questions or thoughts to share with us, make use of the feedback form below.

If You Appreciate What We Do Here On TecMint, You Should Consider:

TecMint is the fastest growing and most trusted community site for any kind of Linux Articles, Guides and Books on the web. Millions of people visit TecMint! to search or browse the thousands of published articles available FREELY to all.

If you like what you are reading, please consider buying us a coffee ( or 2 ) as a token of appreciation.

We are thankful for your never ending support.

Источник

How to Clear Linux Command Line History

You may want to clear the history file and the screen for security reasons. Some Linux distributions may clear the screen when you logout but others do not. Many programs read input as a single line at a time.

The GNU history library is able to keep track of those lines, associate arbitrary data with each line, and utilize information from previous lines in composing new ones. Bash and other shells may use this history library. The default file is

Bash’s history feature

bash’s history function depends on a variable called HISTFILE, normally set to the current user’s .bash_history file (located in the user’s home directory). When echoed, it returns the full path and name of the user’s history file, like so:

1) Remove Linux history command

History can be reset with some command but after the operation, if you logout and login in your shell, you will see the same history

a. Delete the previous commands

You can use history -c command to clear the previous history command in the current shell. That’s enough (but overkill) if you’ve just typed your password and haven’t exited that shell or saved its history explicitly.

The example below shows our current history

Now let’s use the command.

When you exit bash, the history is saved to the history file. The history created during the current session is appended to the file, entries that are already present are unaffected. Let’s check the new history

Let us add some command to our history.

To overwrite the history file with the current shell’s history, run history -w after history -c command

After login again, let’s us check our history

You can see that our history begin at history -w entry command.

b. Delete a single command

You can delete the history’s entries which you don’t want with the -d option. This will delete the history entry at position offset. But when you close terminal and open it again histories are not deleted. So we finally use history -w to save the changes.

Now, if you want to delete the sixth entry which is mkdir command just use:

You can see that we didn’t have mkdir command entry above.

2) Clear bash completely

To clear the bash history completely on the server, an alternative solution is to link

/.bash_history to /dev/null

However, one annoying side-effect is that the history entries is linked to the memory and it will flush back to the file when you log out. To workaround this, you can use the following command:

3) Turn off bash history

You can stop logging history using one of the two ways: turn it off for all users, or turn off logging history for a single user.

a. Turn off for all users

You can turn off the bash history for all user adding unset HISTFILE line in /etc/profile file. This line deactivate the history file of each user on the system

You need to have the permission to apply the command above

b. Turn off for a specific user

The command above, it is possible to turn off the bash history of a specific user. You just need to indicate his bash_profile file.

Every the user will login, his history will be reset as below. All his history command will save until user logout

c. Edit .bashrc

You can remove the history command by editing two values of history command parameters.

• HISTSIZE which is the number of lines or commands that are stored in memory in a history list while your bash session is ongoing
• HISTFILESIZE which saves the amount of lines used for the history stack when it’s written to the history file.

To do it, edit your .bashrc and add

Now you can successfully delete the bash history and even stop logging to bash history using any of the above-listed commands.

4) Delete some entries lines

You can use history -d offset built in to delete a specific line from the current shell’s history. It’s not really practical if you want to remove a range of lines since it only takes one offset as an argument, but you could wrap it with a loop.

Just this one liner in the command prompt will help.

for i in <1..N>; do history -d START_NUM; done

Where START_NUM is starting position of entry in history N is no of entries you may want to delete.

Let’s check the last 15 entries of our history command

Now let us delete 13 entries beginning at the line 986

for i in <1..13>; do history -d 986; done

Now let’s check the result

You can see that we don’t have the same result.

When a user logs in with either a login or interactive/non-login shell, the user’s .bash_history file is opened. Now can operate on this file with some useful commands. The history is useful to retrieve commands used before but you can need to delete some entries of theses used commands. The

/.bash_history file does not record what you type in response to other programs’ prompts, just what you type at the bash prompt itself.

Источник

How To Clear Command Line History In Linux

In Bash, all the commands that you run in the Terminal are stored in a text file named in .bash_history in your home directory. We can use the history command to display a list of the commands entered since you started the session. For some reason, you may want to delete all or a specific command from the Bash history. In this brief guide, let us learn how to clear command line history in Linux with examples.

Before getting to the topic, first let us see why should we clear the command line history and why shouldn’t we do it in some cases.

Why should we clear Command line history?

There are chances that you don’t want to expose the Command line history of your Linux system. Say for example, if you are a Linux trainer/tutor, you might have taught some commands to your students in the Lab computer.

Those commands might be harmful and are not supposed to use. But the students may not fully aware of the consequences of such critical commands.

A curious student might search the command line history, and wonder what does those commands will do, and start to test them one by one. The result? He/she might inadvertently break the system.

Would you allow that? Of course, we can re-install or repair the system in couple minutes. However, it is completely unnecessary if you are bit careful. So, clearing Command line history from time to time, especially in a shared computer, is a good practice.

It is just an example. There could be many other reasons to clear Linux command line history.

Why shouldn’t we clear Command line history?

Clearing Command line history is a good practice, however you must not clear history in some cases. Say for example, you want to repeat a specific command often. Would you type the same command every time? That’s not necessary.

As I said earlier, the commands that you run on the Terminal will be retained in the

/.bash_history file. You can retrieve the previously executed commands by pressing the UP arrow in the keyboard.

When you hit the UP, the list of commands that you run recently will appear. Just keep hitting the UP arrow key until you find the command that you want to run. Once you find the command that you want to run, just hit ENTER to execute. That’s it. You don’t have to type the entire command every time.

Sometimes you can’t remember some lengthy and complex commands in a previous session. In such cases, you can use history command to retrieve the previously executed commands.

So if you already cleared the Bash history, you can access the previously entered commands. This is why you should decide whether you want to clear the command line history or not.

Without further ado, let us see how to clear command line history in Linux.

Clear Command line history in Linux

There are many ways to clear Command line history. Here I have listed five ways.

1. Clear entire Command line history using history command

As stated earlier, the history command will display the last executed commands.

To view the previously executed commands in Linux, run:

To clear the history, just run any one of the following commands:

The above commands will clear the command line history.

2. Avoid saving commands in history list by inserting a blank space before each command

Using this method, you can eliminate a specific command getting saved in the history list. Just put a blank space (Hit space bar from the keyboard) before any command. The command will not be recorded in history.

To do that, you must set HISTCONTROL environment variable’s value as “ignorespace” or “ignoreboth”.

Add the following line at the end:

Save and close the file. Run the following command to take effect the changes.

Or, simply log out and log back in to apply the changes.

To verify it, run a few commands. And put a blank space in-front of any command. I put a blank space in last command.

Here indicates a blank space.

Refer the following screenshot:

Put a blank space before a command to avoid saving it in history in Linux

Now, run the history command to view the recently executed commands:

Sample output:

clear Command line history in Linux

As you see in the above output, the «sudo ping ostechnix.com» command is not displayed in the history command output.

3. Clear or delete specific commands from history

Sometimes you might want to delete some particular commands from history list, instead of clearing the entire history.

Let me show you an example. I am going to run the following commands in the Terminal.

Then, display the history command output using command:

sample output:

As you see in the above output, the history command displays the last executed commands.

To clear or delete a particular command from the history, use -d flag with the command prefix number:

Here represents the line number of each command.

For example, to delete the «time» command with line number «5» from the history, run:

Now, display the command line history to see if the command is removed or not.

Sample output:

Clear or delete specific commands from history

As you see, the «time» command has been removed. Similarly, you can delete any command from the history list.

4. Clear Command line history automatically at logout

Instead of manually clearing history each time, you can automatically clear it at logout.

Add the following line:

Save and close the file. Now, the history will be cleared after you logout from the session.

5. Delete Command line history permanently

All of the above methods will only remove the commands from the active session i.e currently opened terminal. If you have multiple terminals running different commands, the history command will only delete the history from where you run this command. The commands from other terminals will still be available.

To remove all commands from Bash history in all sessions, you must remove the contents of .bash_history file. This file contains the list of commands that we run in the terminal. You can either clear this file manually each time or setup a cron job to clear it at regular intervals.

To manually clear the contents of this file, run:

Like I said, this will delete the entire history. The next time this file will start to record the history. You should run this command everyday to clear the contents of this file.

Alternatively, you can schedule this task at regular interval using cron jobs.

Add the following commands:

Save and exit file. The history will be automatically cleared at 8 pm everyday.

Recommended read:

Conclusion

In this tutorial, you have learned why should we clear the command line history, and why you shouldn’t do it in some cases. Also, you have learned the different ways to clear command line history in Linux. If you know any other method to do it, feel free to let us know in the comment section below.

Источник