How to clear Command line history in Linux/Centos
Sunday, March 19, 2017
How to delet Command line history in Linux/Centos :-
Clear Command line history in Linux/Centos -
There are lot of ways to clear Command line history.
1. Clear entire Command line history using ‘history’ command
To view the recently-executed commands -
>history
To clear the history, just run any one of the following command after you’re done:
>history -c
Or
>history -cw
2. Clear a Command line history using by inserting a blank space before each command
using this way, we can clear/delete any particular command from the history. we need to put a blank space 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”.
export HISTCONTROL=ignorespace
Now, Let us see an example. I ran the following commands. And, I put a blank space in-front of the last command.
>clear
>uname -a
>sudo pacman -Syyu
>sudo wifi-menu
>ls
>
Now, run the ‘history’ command to view the recent-executed commands.
history
Sample output:
3 clear
4 export HISTCONTROL=ignorespace
5 clear
6 uname -a
7 sudo pacman -Syyu
8 sudo wifi-menu
9 ls
10 history
3. Clear or delete specific commands from history
This is another useful way to delete a particular command. Sometimes you might want to delete some critical commands, which causes damage to the system, from the history. This method will be helpful if you don’t want to clear the entire history.Let us see an example. I ran the following commands.
>clear
>cal
>time
>ls
>uname -r
display the history command output:
history
sample output:
3 clear
4 cal
5 time
6 ls
7 uname -r
8 history
As you see in the above output, the history command displays the recently-executed commands.
To clear or delete a particular command from the history, do:
history -d
Here represents the line number of each command. For example, let us delete the “time” command with line number “5” from the history.
To do so, run:
history -d 5
Now, display the command line history to see if the command is remove or not.
history
Sample output:
3 clear
4 cal
5 ls
6 uname -r
7 history
8 history -d 5
9 history
4. Delete Command line history permanently
One problem of using all above methods is they will only remove the commands from the active session i.e currently opened Terminal. That means 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 history in all sessions (Terminals), you must remove the contents of .bash_history file. As you might know already, this file holds the list of commands that we run in the Terminal over time.
You can either clear this file manually each time or setup a cron job to clear it at regular intervals.
To clear the contents of this file manually each time, run:
cat /dev/null > ~/.bash_history
Like I said, this will delete the entire history of all sessions. The next day, however, 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.
To do so, run:
crontab -e
Add the following commands:
00 20 * * * cat /dev/null > ~/.bash_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 command often. Would you type the command every time? That’s not necessary. Like I said already, the commands that you run on the Terminal will be retained in the ~/.bash_history file. Just hit the upper arrow in the keyboard, the list commands that you run recently will appear. Keep hitting the upper 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 command each time. Also, sometimes you won’t remember exactly how you executed a command in a previous session. In such cases, history command will come in help.
