1. Overview
When we work with the command-line under Linux, recent commands will be kept inside history. In this tutorial, we’ll address different ways of deleting a sequence of lines from history.
2. Difference Between history and Commands in .bash_history
Linux bash history is usually stored in a file named ~/.bash_history at the end of each session.
By default, all the commands issued during the session will be saved to this file for further reuse. In each session, when we exit the bash, all the in-memory commands will be written to ~/.bash_history file. So, our current executed commands won’t be saved instantly. Therefore, the current contents of the history command and bash_history file are usually different.
Let’s check the last five lines of the ~/.bash_history file:
$ tail -5 ~/.bash_history
tail
tail
cd
ls
ls
With the -5 option with tail, we can have the five recent commands in the bash_history. Note that these lines belong to the previous session activity. Let’s also check the last five lines in history for comparison:
$ history 5
1987 cd baeldung
1988 ls -l
1989 cat pro.sh
1990 ls -la
1991 echo "${BASH_VERSION}"
These lines belong to our session activity and are not written to bash_history yet.
2. Delete Last n Lines from .bash_history
If we want to delete the last n lines of previous sessions or if we ended our session recently, we should delete lines from ~/.bash_history. Let’s remove the last five lines from this file:
$ for h in {1..5}; do sed -i '$d' ~/.bash_history; done;
The -i option in sed allows for in-place editing. $ matches with the last lines of the file, and d is for deleting the selected line.
Note that we can also open ~/.bash_history file with any text editor and delete the lines manually.
3. Delete Last n Lines in history
If we notice the history records, we can see that each record has a line number. We can use this number to delete a sequence of lines:
$ for h in {1987..1991}; do history -d 1987; done
The history -d option will delete the line with a given line number. In this scenario, we only need to specify the start number in history -d, because after deleting the line 1987, line 1988 will be the line 1987, and so on.
If we want to remove the evidence, we can change the previous command and add a command to delete the last line of history, which is our recent deletion command:
$ for h in {1987..1991}; do history -d 1987; done; history -d $(history 1 | awk '{print $1}')
We get the last line in history with history 1. Then we get the line number with $1.
3.1. Create a Function
We can add the previous line to a new function in ~/.bashrc for further calls.
Let’s edit the ~/.bashrc file:
$ nano ~/.bashrc
Let’s create a new function at the end of ~/.bashrc:
historyDel() {
for h in {$1..$2}; do
history -d $1
done
history -d $(history 1 | awk '{print $1}')
}
Note that making any changes to ~/.bashrc will only work in a new terminal session. To apply changes to the current terminal, we should reload the .bashrc content:
$ source ~/.bashrc
Let’s now call our function in the terminal:
$ historyDel 2001 2004
Note that the historyDel function takes 2 parameters as a range. If we want to delete the last n lines automatically, we can make another function to get n as input:
historyDeln() {
n=$(history 1 | awk '{print $1}') # current history number
historyDel $(( $n-$1 )) $(( $n-1 )) # Call historyDel with ranges
}
Let’s remove the last 5 lines of history with our new function:
$ historyDeln 5
4. Changes in History Since Bash 5
Due to changes in bash 5, there is now a range option available for deleting lines in history. Let’s delete lines of 2001 to 2004 from history:
history -d 2001-2004
Note that the first number is the starting point, and the second one is the endpoint for deletion. The positions are inclusive. Also, we can use backward deletion. Let’s delete the last 5 lines of history:
$ history -d -5--1
A negative index counts back from the end of the history. Therefore, an index of -1 refers to the current history -d command.
5. Conclusion
In this article, we have addressed different ways of removing the last n lines from the Bash commands history.
First, we saw how to delete lines from the .bash_history file. Then, we removed a sequence of commands from history. Finally, we created a function in .bashrc to automate the deletion process.