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17 Bash History Command Examples In Linux

The ‘history’ command available in Bash can be used to simply display your shell history, however there’s also a whole lot more that you can do with it, which we’ll demonstrate here.

Bash history allows us to quickly see what has been executed previously on a system, allowing you to hold users at least somewhat accountable for their actions (more on this later). It’s also useful if you’ve run something before and forgot the command, I can’t begin to tell you the number of times that I’ve done this!

How To Use Bash History – Command Examples

1. Print History

In its most simple form, you can run the ‘history’ command by itself and it will simply print out the bash history of the current user to the screen. Commands are numbered, with older commands at the top and newer commands at the bottom.

[[email protected] ~]$ history 1 ip a 2 exit 3 ls -la 4 pwd [[email protected] ~]#

2. Print ‘n’ Lines

While the default is to print all history lines, you can specify a number after the history command to output this amount of the most recent lines.

[[email protected] ~]$ history 3 16 passwd 17 getenforce 18 history 3

3. Repeat Most Recent Command

[[email protected] ~]# date Sun Aug 28 03:14:55 PDT 2016 [[email protected] ~]# !! date Sun Aug 28 03:14:57 PDT 2016

4. Repeat Specific Command

As shown above, the bash history command displays line numbers. It is possible to repeat a command by specifying its line number.

[[email protected] ~]# history 2 101 date 102 history 2 [[email protected] ~]# !101 date Sun Aug 28 03:18:55 PDT 2016

5. Repeat Command Starting With A String

We can repeat the last command starting with a specified string. This is done with !string, where string is the start of a previously executed command.

[[email protected] ~]# systemctl start httpd [[email protected] ~]# systemctl stop chronyd [[email protected] ~]# systemctl restart chronyd [[email protected] ~]# !systemctl systemctl restart chronyd

As shown the most recent command that started with ‘systemctl’ has been run again. While useful, this can obviously be dangerous if the last command is actually different from what you expect. You can run this with ‘:p’ on the end to instead print the command rather than execute it straight away.

[[email protected] ~]# !systemctl:p systemctl stop chronyd

6. Piping History

We can of course pipe the output of the history command into many other useful commands, such as less or grep. When piping into less we can scroll through the output of the history file rather than having it all output to the terminal. By outputting to grep we can search for commands that have been run previously.

[[email protected] ~]# history | grep httpd 65 yum install httpd -y 106 systemctl stop httpd 107 systemctl start httpd 117 history | grep httpd

7. Write To History File

Usually the history file is written to upon logout, therefore if you have an SSH session that has timed out you will not have your history from that session when you log back in. We can force the current history to write to the users ~/.bash_history file with the -w option.

8. Clear History File

9. Delete Specific Line

Clearing the whole history file may be overkill, we can instead delete a specific line number from the history file with the -d option.

[[email protected] ~]# history | grep password 121 Sun 28 Aug 2016 03:33:11 AM PDT mysql -u root -p oops_this_is_my_password 122 Sun 28 Aug 2016 03:33:19 AM PDT history | grep password [[email protected] ~]# history -d 121 [[email protected] ~]# history | grep password 121 Sun 28 Aug 2016 03:33:19 AM PDT history | grep password 123 Sun 28 Aug 2016 03:33:29 AM PDT history | grep password

10. Run Single Command Without Logging

[[email protected] ~]# echo "secret command";history -d $(history 1) secret command

11. Run All Commands Without Logging

Additionally we can unset the history file variable for the current bash session which will prevent all history for the current session from being stored.

[[email protected] ~]# echo $HISTFILE /root/.bash_history [[email protected] ~]# unset HISTFILE [[email protected] ~]# echo $HISTFILE 

Note that this is not permanent, when you log out and log back in HISTFILE will be reset back to the default. This example will allow you to have an unlogged session, though you could specify the unset in ~/.bashrc to never log history.

12. Ignore Specific Commands

We can specify a list of commands that should never be logged in the history file with the $HISTIGNORE variable, which is not set by default.

[[email protected] ~]# echo 'export HISTIGNORE="ls:cd"' >> ~/.bashrc 

[[email protected] ~]# ls anaconda-ks.cfg new_history [[email protected] ~]# pwd /root [[email protected] ~]# cd [[email protected] ~]# echo hi hi [[email protected] ~]# history 5 123 history 124 du 125 pwd 126 echo hi 127 history 5

13. Increase History Size

By default 1000 lines of history will be stored, as per the values stored in the $HISTSIZE and $HISTFILESIZE variables.

[[email protected] ~]# echo $HISTFILESIZE 1000 [[email protected] ~]# echo $HISTSIZE 1000

The default for all users is stored in the /etc/profile file, this can be modified or you can otherwise append the following lines to the bottom of ~/.bashrc which will apply to that user at next login.

HISTSIZE=2000 HISTFILESIZE=2000

14. Add Timestamps To History

As you may have noticed by default we are not able to see the date and time that commands were executed, merely their order. We can set the $HISTTIMEFORMAT variable with a specific date and time format, the easiest option is to use %c as shown below.

echo 'export HISTTIMEFORMAT="%c "' >> ~/.bashrc

Once this user logs out and back in for the export to execute, the existing history file will show all contents as executing at the exact same time as the time information was not previously recorded. From here onward however, the date and time will be stored with each command in the bash history file.

[[email protected] ~]# history 5 39 Sun 28 Aug 2016 02:37:54 AM PDT firewall-cmd --add-service=http --permanent 40 Sun 28 Aug 2016 02:37:54 AM PDT firewall-cmd --reload 41 Sun 28 Aug 2016 02:37:54 AM PDT tailf /var/log/messages 42 Sun 28 Aug 2016 02:37:54 AM PDT restorecon -v /var/www/html/index.html 43 Sun 28 Aug 2016 02:49:27 AM PDT history 5

15. Change History File Location

By default the bash history is written to ~/.bash_history, this is set in the $HISTFILE variable as shown below.

[[email protected] ~]# echo $HISTFILE /root/.bash_history [[email protected] ~]# su - user [[email protected] ~]$ echo $HISTFILE /home/user/.bash_history

[[email protected] ~]# echo 'export HISTFILE="/root/new_history"' >> ~/.bashrc 

16. Do Not Store Duplicate Commands

By default /etc/profile sets the $HISTCONTROL variable to ‘ignoredups’ which will ignore duplicate commands that are run one after the other. For example if we execute the ‘pwd’ command multiple times, it will only show once in the history.

[[email protected] ~]# pwd /root [[email protected] ~]# pwd /root [[email protected] ~]# pwd /root [[email protected] ~]# pwd /root [[email protected] ~]# history | grep pwd 1 Sun 28 Aug 2016 04:01:07 AM PDT pwd 2 Sun 28 Aug 2016 04:01:15 AM PDT history | grep pwd

17. Reverse Search

While we can browse previous commands with the techniques previously listed, my favourite is reverse search which is executed with ‘ctrl+r’. After pressing ‘ctrl+r’ you will see the the (reverse-i-search)`’: prompt, at this point you can start typing a command that has previously been executed and it will display the most recent command. You can cycle back further through previous commands that also contain this string by pressing ‘ctrl+r’ again and again until you find what you’re after.

(reverse-i-search)`httpd': systemctl start httpd

All history should also be taken with a grain of salt, as it is very easy to modify as by default a user has write permissions on their own ~/.bash_history file so they can modify it however they want, including deleting the contents to cover their tracks.

You could instead look at sending bash history to an external syslog server so that it cannot be modified, but that’s a story for another time.

Summary

As shown the history command is quite powerful, it allows us to view command history on a Linux system using Bash with a number of customizations available.

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How to Repeat Your Last Command in Linux?

Linux terminal allows us to execute a variety of commands and sometimes it so happens that we find ourselves in a scenario where we might want to use a certain command more than once.

There are many occurrences where we would want to repeat the command that we just ran. In Linux, this can be done with the help of different commands, and in this tutorial, we will explore all such commands with the help of different examples.

For reference and simplicity, I will run a single command, say ‘ls -ltr’ and then use the different methods to search what was the last command that I ran.

The most basic approach to run the command that we just ran is to press the UPPER arrow key of the keyboard, and we will get the last command back in the terminal. However, there are multiple other ways with which we can repeat the last command. Let’s understand them one by one with the help of examples.

Repeating the Last Command Using Exclamation Marks

Yes, by using the exclamation marks, you can repeat the last command that you just typed on the terminal. Consider the command shown below.

We just need to write the above command in the terminal, and the terminal will automatically output the last command that we used before the above command.

For reference, let’s just suppose that we used the command ‘ls –ltr’, and then enter the above command in the terminal. Then, the output that we get after running the above command is shown below.

root@imml97:~# !! ls -ltr total 0

Notice how it tells us what command we used the last, and also gives us the output of that command as well.

Using Hyphen and Prefix of Command

Now we will use the hyphen symbol and will also pass the number which will tell the compiler to give us the last command that we just used. Consider the following command −

We just need to write the above command in the terminal, and the terminal will automatically output the last command that we used before the above command.

Using CTRL + P

You can use a combination of command (CTRL + P) to output the last command that you used in the terminal. You can use this combination multiple times to traverse through the entire set of commands that you used previously.

Using CTRL + P and CTRL + R

You can use a combination of ‘CTRL + P’ and ‘CTRL + R’ to output the last command that you used on the terminal. And then, if you press the button after this combination, you will also be able to run that command as well.

Using ‘fc’ Command

You can also use the following ‘fc’ command to output the last command that you used on the terminal.

We just need to write the above command on the terminal, and the terminal will automatically output the last command that we ran before the above command.

Conclusion

In this tutorial, we used multiple examples to demonstrate how you can use different commands to get the last command that we used in the terminal.

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