The Power of Linux “History Command” in Bash Shell

We use history command frequently in our daily routine jobs to check history of command or to get info about command executed by user. In this post, we will see how we can use history command effectively to extract the command which was executed by users in Bash shell. This may be useful for audit purpose or to find out what command is executed at what date and time.

By default date and timestamp won’t be seen while executing history command. However, bash shell provides CLI tools for editing user’s command history. Let’s see some handy tips and tricks and power of history command.

The Power of Linux “History Command” in Bash Shell

history command examples

1. List Last/All Executed Commands in Linux

Executing simple history command from terminal will show you a complete list of last executed commands with line numbers.

[[email protected] ~]$ history

    1  PS1='/e[1;35m[/[email protected]/h /w]$ /e[m '
    2  PS1="/e[0;32m[/[email protected]/h /W]$ /e[m "
    3  PS1="/[email protected]/h:/w [/j]$ "
    4  ping google.com
    5  echo $PS1
    6   tail -f /var/log/messages
    7  tail -f /var/log/messages
    8  exit
    9  clear
   10  history
   11  clear
   12  history

2. List All Commands with Date and Timestamp

How to find date and timestamp against command? With ‘export’ command with variable will display history command with corresponding timestamp when the command was executed.

[[email protected] ~]$ export HISTTIMEFORMAT='%F %T  '

      1  2013-06-09 10:40:12   cat /etc/issue
      2  2013-06-09 10:40:12   clear
      3  2013-06-09 10:40:12   find /etc -name *.conf
      4  2013-06-09 10:40:12   clear
      5  2013-06-09 10:40:12   history
      6  2013-06-09 10:40:12   PS1='/e[1;35m[/[email protected]/h /w]$ /e[m '
      7  2013-06-09 10:40:12   PS1="/e[0;32m[/[email protected]/h /W]$ /e[m "
      8  2013-06-09 10:40:12   PS1="/[email protected]/h:/w [/j]$ "
      9  2013-06-09 10:40:12   ping google.com
     10  2013-06-09 10:40:12   echo $PS1
Meaning of HISTTIMEFORMAT variables
%F Equivalent to %Y - %m - %d
%T Replaced by the time ( %H : %M : %S )

3. Filter Commands in History

As we can see same command is being repeated number of times in above output. How to filter simple or non destructive commands in history?. Use the following ‘export‘ command by specifying command in HISTIGNORE=’ls -l:pwd:date:’ will not saved by system and not be shown in history command.

[[email protected] ~]$ export HISTIGNORE='ls -l:pwd:date:'

4. Ignore Duplicate Commands in History

With the below command will help us to ignore duplicate commands entry made by user. Only single entry will be shown in history, if a user execute a same command multiple times in a Bash Prompt.

[[email protected] ~]$ export HISTCONTROL=ignoredups

5. Unset export Command

Unset export command on the fly. Execute unset export command with variable one by one whatever commands have been exported by export command.

[[email protected] ~]$ unset export HISTCONTROL

6. Save export Command Permanently

Make an entry as follows in .bash_profile to save export command permanently.

[[email protected] ~]$ vi .bash_profile

# .bash_profile

# Get the aliases and functions
if [ -f ~/.bashrc ]; then
        . ~/.bashrc
fi

# User specific environment and startup programs

export HISTCONTROL=ignoredups

PATH=$PATH:$HOME/bin
export PATH

7. List Specific User’s Executed Commands

How to see command history executed by a specific user. Bash keeps records of history in a ‘~/.bash_history’ file. We can view or open file to see the command history.

[[email protected] ~]$ vi .bash_history

cd /tmp/
cd logstalgia-1.0.3/
./configure
sudo passwd root
apt-get install libsdl1.2-dev libsdl-image1.2-dev libpcre3-dev libftgl-dev libpng12-dev libjpeg62-dev make gcc
./configure
make
apt-get install libsdl1.2-dev libsdl-image1.2-dev libpcre3-dev libftgl-dev libpng12-dev libjpeg62-dev make gcc++
apt-get install libsdl1.2-dev libsdl-image1.2-dev libpcre3-dev libftgl-dev libpng12-dev libjpeg62-dev make gcc
apt-get install make
mysql -u root -p
apt-get install grsync
apt-get install unison
unison

8. Disable Storing History of Commands

Some organization do not keep history of commands because of security policy of the organization. In this case, we can edit .bash_profile file (It’s hidden file) of user’s and make an entry as below.

[[email protected] ~]$ vi .bash_profile

# .bash_profile

# Get the aliases and functions
if [ -f ~/.bashrc ]; then
        . ~/.bashrc
fi

# User specific environment and startup programs

PATH=$PATH:$HOME/bin
HISTSIZE=0
export PATH
.bash_profile (END)

Save file and load changes with below command.

[[email protected] ~]$ source .bash_profile

Note: If you don’t want system to remember the commands that you have typed, simply execute below command which will disable or stop recording history on the fly.

[[email protected] ~]$ export HISTSIZE=0

Tips: Search ‘HISTSIZE‘ and edit in ‘/etc/profile’ file with superuser. The change in file will effect globally.

9. Delete or Clear History of Commands

With up and down arrow, we can see previously used command which may be helpful or may irate you. Deleting or clearing all the entries from bash history list with ‘-c‘ options.

[[email protected] ~]$ history -c

10. Search Commands in History Using Grep Command

Search command through ‘.bash_history‘ by piping your history file into ‘grep‘ as below. For example, the below command will search and find ‘pwd‘ command from the history list.

[[email protected] ~]$ history | grep pwd

  113  2013-06-09 10:40:12     pwd
  141  2013-06-09 10:40:12     pwd
  198  2013-06-09 15:46:23     history | grep pwd
  202  2013-06-09 15:47:39     history | grep pwd

11. Search Lastly Executed Command

Search previously executed command with ‘Ctrl+r’ command. Once you’ve found the command you’re looking for, press ‘Enter‘ to execute the same else press ‘esc‘ to cancel it.

(reverse-i-search)`source ': source .bash_profile

12. Recall Last Executed Command

Recall a previously used specific command. Combination of Bang and 8 (!8) command will recall number 8 command which you have executed.

[[email protected] ~]$ !8

13. Recall Lastly Executed Specific Command

Recall previously used command (netstat -np | grep 22) with ‘!‘ and followed by some letters of that particular command.

[[email protected] ~]$ !net
netstat -np | grep 22
(No info could be read for "-p": geteuid()=501 but you should be root.)
tcp        0     68 192.168.50.2:22             192.168.50.1:1857           ESTABLISHED -
tcp        0      0 192.168.50.2:22             192.168.50.1:2516           ESTABLISHED -
unix  2      [ ]         DGRAM                    12284  -                   @/org/freedesktop/hal/udev_event
unix  3      [ ]         STREAM     CONNECTED     14522  -
unix  2      [ ]         DGRAM                    13622  -
unix  3      [ ]         STREAM     CONNECTED     12250  -                   @/var/run/hald/dbus-ujAjOMNa0g
unix  3      [ ]         STREAM     CONNECTED     12249  -
unix  3      [ ]         STREAM     CONNECTED     12228  -                   /var/run/dbus/system_bus_socket
unix  3      [ ]         STREAM     CONNECTED     12227  -

We have tried to highlight power of history command. However, this is not end of it. Please share your experience of history command with us through our comment box below.

Source: tecmint.com

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