When you are using Linux command line frequently, using the history command effectively can be a major productivity boost.
In Linux, there is a very useful command to show you all of the last commands that have been recently used. The command is simply called history
.
Table of Contents
- Display Timestamp
- Searching Command History
- Repeat the Last Executed Command
- Execute a Specific Command
- Execute Previous Command That Starts with a Specific Word
- Limit the Number of History Items
- Change the History File Name
- Eliminate the Continuous Repeated Entry from History
- Erase Duplicates Across the Whole History
- Force History Not to Remember a Particular Command
- Clear All the Previous History
- Substitute Words from History Commands
- Substitute a Specific Argument for a Specific Command
- Disable the Usage of History
- Ignore Specific Commands from the History
Display Timestamp
Typically when you type history
in command line, by default you see a number followed by the commands you’ve used recently. For auditing purpose, it may be beneficial to display the timepstamp along with the command as shown below.
To enable timestamp in history
command output, you must configure the HISTTIMEFORMAT
Bash variable.
export HISTTIMEFORMAT="%F %T "
history | more
1 2020-06-25 19:02:39 systemctl restart network
2 2020-06-25 19:02:43 exit
3 2020-06-25 19:02:47 id
4 2020-06-25 19:02:56 cat /etc/hosts
Searching Command History
This may be your most frequently used feature of the history
command. When you’ve already executed a very long command, you can simply search history using a keyword and re-execute the same command without having to type it fully.
- Press
Control+R
and type the keyword. - Press enter when you see your command, which will execute the command from the history.
In the following example, I searched for host
, which displayed the previous command cat /etc/hosts
in the history that contained the word host
.
(reverse-i-search)`host': cat /etc/hosts
cat /etc/hosts
#<ip-address> <hostname.domain.org> <hostname>
127.0.0.1 localhost.localdomain localhost server1
::1 localhost.localdomain localhost server1
Sometimes you want to edit a command from history before executing it. For example, you can search for systemctl
, which will display systemctl restart network
from the command history, select this command (pressing ESC
key) and change the restart
to stop
.
Then re-execute it again by just hitting Enter
.
(reverse-i-search)`systemctl': systemctl stop network
systemctl stop network
Repeat the Last Executed Command
Sometime you may end up repeating the previous commands for various reasons. Following are the 4 different ways to repeat the last executed command.
- Use the
up arrow
to view the previous command and press enter to execute it. - Type
!!
and press enter from the command line - Type
!-1
and press enter from the command line. - Press
Control+P
will display the previous command, press enter to execute it.
Execute a Specific Command
In the following example, if you want to repeat the command #4, you can do !4
as shown below.
history | more
systemctl restart network
exit
id
cat /etc/hosts
!4
cat /etc/hosts
#<ip-address> <hostname.domain.org> <hostname>
127.0.0.1 localhost.localdomain localhost server1
::1 localhost.localdomain localhost server1
Execute Previous Command That Starts with a Specific Word
Type !
followed by the starting few letters of the command that you would like to re-execute. In the following example, typing !ps
and enter, executed the previous command starting with ps
, which is ps aux | grep yp
.
!ps
ps aux | grep yp
root 16947 0.0 0.1 36516 1264 ? Sl 13:10 0:00 ypbind
root 17503 0.0 0.0 4124 740 pts/0 S+ 19:19 0:00 grep yp
Limit the Number of History Items
This is controlled by the HISTSIZE
and HISTFILESIZE
built-in Bash shell variables. Append the following two lines to your ~/.bashrc
file and log out and then log back in.
HISTSIZE=1500
HISTFILESIZE=1500
As a result, now history
is set to store 1500 commands.
Change the History File Name
By default, history
is stored in ~/.bash_history
file.
Add the following line to the .bash_profile
file and relogin to the Bash shell, to store the history command in .my_commandline
file instead of .bash_history
file.
HISTFILE=/root/.my_commandline
This getting used when you want to track commands executed from different terminals using different history file name.
Eliminate the Continuous Repeated Entry from History
In the following example pwd
was typed three times, when you do history, you can see all the 3 continuous occurrences of it. To eliminate duplicates, set HISTCONTROL
to ignoredups
as shown below.
history | tail -4
44 pwd
45 pwd
46 pwd
47 history | tail -4
export HISTCONTROL=ignoredups
history | tail -3
56 export HISTCONTROL=ignoredups
57 pwd
58 history | tail -4
Erase Duplicates Across the Whole History
The ignoredups
shown above removes duplicates only if they are consecutive commands. To eliminate duplicates across the whole history, set the HISTCONTROL
to erasedups
as shown below.
export HISTCONTROL=erasedups
pwd
systemctl restart network
history | tail -3
38 pwd
39 systemctl restart network
40 history | tail -3
ls -l
systemctl restart network
history | tail -6
35 export HISTCONTROL=erasedups
36 pwd
37 history | tail -3
38 ls -l
39 systemctl restart network
40 history | tail -6
Force History Not to Remember a Particular Command
When you execute a command, you can instruct history
to ignore the command by setting HISTCONTROL
to ignorespace
and typing a space in front of the command as shown below.
I can see lot of junior sysadmins getting excited about this, as they can hide a command from the history. It is good to understand how ignorespace
works. But, as a best practice, don’t hide purposefully anything from history.
export HISTCONTROL=ignorespace
ls -ltr
pwd
systemctl restart network #Note that there is a space at the beginning of service, to ignore this command from history
history | tail -3
67 ls -l
68 pwd
69 history | tail -3
Clear All the Previous History
Sometime you may want to clear all the previous history
, but want to keep the history moving forward.
history -c
Substitute Words from History Commands
When you are searching through history
, you may want to execute a different command but use the same parameter from the command that you’ve just searched.
In the example below, the !!:$
next to the vi
command gets the argument from the previous command to the current command.
ls nginx.conf
nginx.conf
vi !!:$
vi nginx.conf
In the example below, the !^
next to the vi command gets the first argument from the previous command (i.e cp
command) to the current command (i.e vi
command).
cp nginx.conf nginx.conf.bak
vi !^
vi nginx.conf
Substitute a Specific Argument for a Specific Command
In the example below, !cp:2
searches for the previous command in history that starts with cp and takes the second argument of cp and substitutes it for the ls -l command as shown below.
cp ~/longname.txt /really/a/very/long/path/long-filename.txt
ls -l !cp:2
ls -l /really/a/very/long/path/long-filename.txt
In the example below, !cp:$
searches for the previous command in history that starts with cp and takes the last argument (in this case, which is also the second argument as shown above) of cp and substitutes it for the ls -l command as shown below.
ls -l !cp:$
ls -l /really/a/very/long/path/long-filename.txt
Disable the Usage of History
If you want to disable history
all together and don’t want Bash shell to remember the commands you’ve typed, set the HISTSIZE
to 0 as shown below.
export HISTSIZE=0
Ignore Specific Commands from the History
Sometimes you may not want to clutter your history with basic commands such as pwd
and ls
. Use HISTIGNORE
to specify all the commands that you want to ignore from the history.
Please note that adding ls
to the HISTIGNORE
ignores only ls
and not ls -l
. So, you have to provide the exact command that you would like to ignore from the history.
export HISTIGNORE="pwd:ls:ls -ltr:"
pwd
ls
ls -l
systemctl restart network
history | tail -3
79 export HISTIGNORE="pwd:ls:ls -l:"
80 systemctl restart network
81 history
[Note that history did not record pwd, ls and ls -l]
For more about the history
command in Linux, consult its manual page.