Mastering Linux Command line history

Search the history using Control+R

If you have already executed a very long command, you can simply search history using a keyword and re-execute the same command without having to fully type it.

Press Control+R and type the keyword.

# [Press Ctrl+R from the command prompt]

It displays the reverse-i-search prompt, like :

(reverse-i-search) : 

Type some part of command and it will display the most related command from history, Like if you type 'red' - 

(reverse-i-search)`shaan': cat /etc/shaan123.txt

Press enter when you see your command, which will execute the command from the history

# cat /etc/shaan123.txt

Repeat previous command quickly

4 different ways to repeat the last executed command :

   a. Use the up arrow to view the previous command and press enter to execute it.

   b. Type !! and press enter from the command line.

   c. Type !-1 and press enter from the command line.

   d. Press Control+P will display the previous command, press enter to execute it.

Execute a specific command from history

If you want to repeat the command #4, you can do !4 as shown below.

# history | more

1 service network restart

2 exit

3 id

4 cat /etc/shaan123.txt

# !4

# cat /etc/shaan123.txt

Display timestamp using HISTTIMEFORMAT

When you type history from command line, it displays the command prompt and the command.

For auditing purpose, display the timepstamp along with the command, Like :

# 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/shaan123.txt

Clear history

Clear all the previous command history using option -c

You may want to clear all the previous history, but want to keep the history moving forward.

# history -c

Some advanced history options

Ignore specific commands from the history using HISTIGNORE

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.

Note : 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 -ltr

# service httpd stop

# history | tail -3

79  export HISTIGNORE="pwd:ls:ls -ltr:"

80  service httpd stop

81  history

Note : history did not record pwd, ls and ls -ltr

Force history not to remember a particular command using HISTCONTROL

When you execute a command, you can instruct history to ignore the command by setting HISTCONTROL to ignorespace.

After this setting, if you type a space in front of the command, it will not be recorded in history.

# export HISTCONTROL=ignorespace

# ls -ltr

# pwd

# service httpd stop

Note : 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

Erase duplicates across the whole history using HISTCONTROL

The ignoredups removes duplicates only if they are consecutive commands.

To eliminate duplicates across the whole history, set the 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 : The previous service httpd stop after pwd got erased

40  history | tail -6

Eliminate the continuous repeated entry from history using HISTCONTROL

In the following example pwd was typed 3 times, when you do history, you can see all the 3 continuous occurrences of it.

To eliminate duplicates, set HISTCONTROL to ignoredups.

# pwd

# pwd

# pwd

# history | tail -4

44  pwd

45  pwd

46  pwd

Note : 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 : There is only one pwd command in the history, even after executing pwd 3 times as shown above.

58  history | tail -4

Control the total number of lines in the history using HISTSIZE

Append the following two lines to the .bash_profile and re-login to the bash shell again to see the change.

In this example, only 450 command will be stored in the bash history.

# vi ~/.bash_profile

HISTSIZE=450

HISTFILESIZE=450