Practice Exercise: Mastering Command Line History and Recall

Objective

Learn to efficiently navigate and utilize the command line history for increased productivity in a Linux environment.

Open a terminal window.
Execute a few simple commands in the terminal.
Use the history command to display a list of recently executed commands, along with their corresponding numbers.

Use the !n command, where n is the command number from the history list, to quickly rerun a specific command.

[intern@intern-a1t-inf-lnx1 ~]$ history
    1  ip a
    2  man apt
    3  unminimize
    4  sudo unminimize
    5  ip a
[intern@intern-a1t-inf-lnx1 ~]$ !1
ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever

Task 2: Command History Expansion

Execute several commands that involve file operations, like creating, moving, or deleting files.
Use the !! command to rerun the last command executed.
Utilize the !$ and !* shortcuts to access the last argument or all arguments from the previous command.

Experiment with the !string syntax to rerun a command that starts with a specific string.

[intern@intern-a1t-inf-lnx1 ~]$ cd /home/projects
[intern@intern-a1t-inf-lnx1 ~]$ !!
cd /home/projects
[intern@intern-a1t-inf-lnx1 ~]$ ls !$
ls /home/projects
project_plan.txt
[intern@intern-a1t-inf-lnx1 ~]$ echo /home/projects /home/intern
/home/projects /home/intern
[intern@intern-a1t-inf-lnx1 ~]$ ls !*
ls /home/projects /home/intern
/home/intern:
'#emacs_code.c#'   emacs_code.c~   incremental.snar             incremental_backup2.tar.gz
 bin               go              incremental_backup           installer_linux
 cri-dockerd       hello.txt       incremental_backup.tar.gz    user.sh
 emacs_code.c      hello_world     incremental_backup1.tar.gz

/home/projects:
project_plan.txt
[intern@intern-a1t-inf-lnx1 ~]$ !e
echo /home/projects /home/intern
/home/projects /home/intern

Task 3: Searching Command History

Execute various commands with descriptive keywords in them.
Use the Ctrl + R keyboard shortcut to initiate a reverse search in the command history.
Start typing a keyword, and the terminal will display the most recent command containing that keyword.
Continue pressing Ctrl + R to cycle through matching commands.

Modify and rerun a command found during the search.

(reverse-i-search)`cd': cd /home/projects
(reverse-i-search)`cd': cd

Task 4: Command History Management

Use the history -c command to clear the entire command history.
Execute a few more commands to populate the history again.
Limit the number of commands stored in the history by setting the HISTSIZE environment variable.
Check the size of your history using echo $HISTSIZE.

Test if new commands are added when the history size is reached.

[intern@intern-a1t-inf-lnx1 ~]$ history -c
[intern@intern-a1t-inf-lnx1 ~]$ history
    1  history
[intern@intern-a1t-inf-lnx1 ~]$ echo $HISTSIZE
1000
[intern@intern-a1t-inf-lnx1 ~]$ export HISTSIZE=5
[intern@intern-a1t-inf-lnx1 ~]$ echo "GG1"
GG1
[intern@intern-a1t-inf-lnx1 ~]$ echo "GG2"
GG2
[intern@intern-a1t-inf-lnx1 ~]$ echo "GG3"
GG3
[intern@intern-a1t-inf-lnx1 ~]$ echo "GG4"
GG4
[intern@intern-a1t-inf-lnx1 ~]$ echo "GG5"
GG5
[intern@intern-a1t-inf-lnx1 ~]$ echo "GG6"
GG6
[intern@intern-a1t-inf-lnx1 ~]$ history
    6  echo "GG3"
    7  echo "GG4"
    8  echo "GG5"
    9  echo "GG6"
   10  history

Task 5: Saving and Exporting Command History

Use the history -w command to write the current command history to a file, such as my_history.txt.
Open the saved history file using a text editor and inspect its contents.
Export the command history to a new terminal session using the history -r command.

Verify that your previous commands are available in the new session.

[intern@intern-a1t-inf-lnx1 ~]$ history -w my_history
[intern@intern-a1t-inf-lnx1 ~]$ cat my_history
echo "GG6"
history
man history
history --help
history -w my_history

Open a new terminal session

[intern@intern-a1t-inf-lnx1 ~]$ history
    1  ip a
    2  man apt
    3  unminimize
    4  sudo unminimize
    5  ip a
[intern@intern-a1t-inf-lnx1 ~]$ history -r /home/projects/my_history
[intern@intern-a1t-inf-lnx1 ~]$ history
  245  history -r /home/projects/my_history
  246  echo "GG6"
  247  history
  248  man history
  249  history --help
  250  history -w my_history
  251  history

Conclusion

In this lab exercise, you've delved into the world of command line history and recall in a Linux environment. You've learned essential techniques for navigating, searching, and managing your command history, which can significantly enhance your efficiency and productivity when working with the command line.