About the history command

If you often use the Linux command line, then using the history command can effectively improve your efficiency. This article will introduce you to 15 usages of the history command by way of examples.

Display timestamps using HISTTIMEFORMAT

When you execute the history command from the command line, usually only the sequence number of the executed command and the command itself are displayed. If you want to see the timestamp of the command history, you can do:

# export HISTTIMEFORMAT='%F %T '
# history | more
1  2008-08-05 19:02:39 service network restart
2  2008-08-05 19:02:39 exit
3  2008-08-05 19:02:39 id
4  2008-08-05 19:02:39 cat /etc/redhat-release

Note: This function can only be used when the HISTTIMEFORMAT environment variable is set, and those newly executed bash commands will be stamped with the correct timestamp. All previous commands will display the time the HISTTIMEFORMAT variable was set. [Added thanks to NightOwl readers]

Use Ctrl+R to search history

Ctrl+R is a shortcut I use a lot. This shortcut allows you to search through the command history, useful when you want to repeat a command. When a command is found, it is usually executed by pressing the Enter key again. If you want to adjust the found command and then execute it, you can press the left or right arrow key.

# [Press Ctrl+R from the command prompt, which will display the reverse-i-search prompt]
(reverse-i-search)`red‘: cat /etc/redhat-release
[Note: Press enter when you see your command, which will execute the command from the history]
# cat /etc/redhat-release
Fedora release 9 (Sulphur)

Quickly repeat the previous command

There are 4 ways to repeat the previous command:

Use the up arrow key and press Enter to execute.
Press !! and enter to execute.
Type !-1 and press Enter to execute.
Press Ctrl+P and press Enter to execute.
Execute a specified command from the command history

In the following example, if you want to repeat the fourth command, you can do !4:

# history | more
1  service network restart
2  exit
3  id
4  cat /etc/redhat-release
# !4
cat /etc/redhat-release
Fedora release 9 (Sulphur)

Execute the previous command by specifying the keyword

In the following example, typing !ps and pressing Enter will execute commands starting with ps:

# !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

Use HISTSIZE to control the total number of lines recorded by the history command

Append the following two lines to the .bash_profile file and log in to the bash shell again, and the number of records in the command history will become 450:

# vi ~/.bash_profile
HISTSIZE=450
HISTFILESIZE=450

Use HISTFILE to change the history file name

By default, the command history is stored in the ~/.bash_history file. Add the following to the .bash_profile file and re-login to the bash shell, the .commandline_warrior will be used to store the command history:

# vi ~/.bash_profile
HISTFILE=/root/.commandline_warrior

Use HISTCONTROL to remove consecutive duplicate entries from the command history

In the example below, the pwd command is executed three times in a row. After executing history you will see three duplicate entries. To weed out these duplicate entries, you can set HISTCONTROL to ignoredups:

# pwd
# pwd
# pwd
# history | tail -4
44  pwd
45  pwd
46  pwd [Note that there are three pwd commands in history, after executing pwd 3 times as shown above]
47  history | tail -4
# export HISTCONTROL=ignoredups
# pwd
# pwd
# pwd
# history | tail -3
56  export HISTCONTROL=ignoredups
57  pwd [Note that there is only one pwd command in the history, even after executing pwd 3 times as shown above]
58  history | tail -4

Use HISTCONTROL to clear duplicate entries from entire command history

The ignoredups in the above example can only remove consecutive duplicate entries. To clear the entire command history of duplicate entries, set HISTCONTROL to erasedups:

# export HISTCONTROL=erasedups
# pwd
# service httpd stop
# history | tail -3
38  pwd
39  service httpd stop
40  history | tail -3
# ls -ltr
# service httpd stop
# history | tail -6
35  export HISTCONTROL=erasedups
36  pwd
37  history | tail -3
38  ls -ltr
39  service httpd stop
[Note that the previous service httpd stop after pwd got erased]
40  history | tail -6

Use HISTCONTROL to force history not to remember specific commands

Set HISTCONTROL to ignorespace and enter a space before commands you don't want to be remembered:

# export HISTCONTROL=ignorespace
# ls -ltr
# pwd
#  service httpd stop [Note that there is a space at the beginning of service, to ignore this command from history]
# history | tail -3
67  ls -ltr
68  pwd
69  history | tail -3

Use the -c option to clear all command history

If you want to clear all command history, you can execute:

# history -c

command substitution

In the following example, !!:$ will get the arguments of the previous command for the current command:

# ls anaconda-ks.cfg
anaconda-ks.cfg
# vi !!:$
vi anaconda-ks.cfg

ADDED: Use !$ to achieve the same effect, but much simpler. [Thanks to wanzigunzi reader for addition]

In the following example, !^ gets the first argument from the previous command:

# cp anaconda-ks.cfg anaconda-ks.cfg.bak
anaconda-ks.cfg
# vi -5 !^
vi anaconda-ks.cfg

Substitute the specified parameter for a specific command

In the following example, !cp:2 searches the command history for commands starting with cp and gets its second argument:

# 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 following example, !cp:$ gets the last parameter of the cp command:

# ls -l !cp:$
ls -l /really/a/very/long/path/long-filename.txt

Disable history with HISTSIZE

If you want to disable history, set HISTSIZE to 0:

# export HISTSIZE=0
# history
# [Note that history did not display anything]

Use HISTIGNORE to ignore specific commands in history

The following example will ignore pwd, ls, ls -ltr, etc. commands:

# export HISTIGNORE=”pwd:ls:ls -ltr:”
# pwd
# ls
# ls -ltr
# service httpd stop
# history | tail -3
79  export HISTIGNORE=”pwd:ls:ls -ltr:”
80  service httpd stop
81  history
[Note that history did not record pwd, ls and ls -ltr]