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1. Overview

In this tutorial, we’ll understand the significance of the Bash HISTFILESIZE and HISTSIZE variables. We’ll also check their default values and how they differ.

2. Bash History and Its Default Behavior

When the Bash shell is loaded interactively on user login, it reads the contents of the history file into memory. During the shell session, it adds content to the in-memory copy of the history.

When we execute the history command on a terminal, Bash reads the in-memory copy to show the history of executed commands. Finally, when the shell exits, it writes the in-memory content back to disk on the file pointed by the HISTFILE environment variable.

By default, the contents are stored in the .bash_history file located at the user’s home directory:

$ echo $HISTFILE
/home/shubh/.bash_history

The number of lines that can be stored in the history file is governed by two special variables HISTSIZE and HISTFILESIZE.

3. HISTSIZE and HISTFILESIZE Variables

The value set in the HISTSIZE variable is the maximum number of lines of history that we can store in memory. Let’s start by checking the default value of the variable:

$ echo $HISTSIZE
500

This means that by default, we can store a maximum of 500 lines in history for a given Bash session.

To better understand the concepts, let’s experiment a bit:

$ HISTSIZE=3
$ echo $HISTSIZE
3

We’ve set the variable to hold only 3 records in memory. Let’s verify by executing the  history command:

$ history
 1502  HISTSIZE=3
 1503  echo $HISTSIZE
 1504  history

Let’s further check the behavior by executing some more commands:

$ echo "Let's add a record to history"
Let's add a record to history
$ history
 2511  history
 2512  echo "Let's add a record to history"
 2513  history

As we can see, we can store only the last 3 commands in the Bash memory.

On the other hand, the HISTFILESIZE variable controls the maximum number of lines that we can write back to the history file on disk.

Let’s check the default value of the variable:

$ echo $HISTFILESIZE
500

Hence by default, we can write a maximum of 500 lines to the ~/.bash_history file.

Consider a situation in which we execute more than 500 commands in a Bash session. Hence on Bash exit, only the last 500 commands are stored back in the history file when the Bash session ends.

4. Understanding the Differences

We’ll now experiment a bit and set the value of HISTFILESIZE smaller than the value of the HISTSIZE:

$ HISTFILESIZE=5 &&  echo $HISTFILESIZE
5
$ HISTSIZE=10 && echo $HISTSIZE
10

Now, let’s execute some test commands on the terminal:

$ echo "Command1" >/dev/null
$ echo "Command2" >/dev/null
$ echo "Command3" >/dev/null
$ echo "Command4" >/dev/null
$ echo "Command5" >/dev/null
$ echo "Command6" >/dev/null
$ echo "Command7" >/dev/null
$ echo "Command8" >/dev/null
$ echo "Command9" >/dev/null
$ echo "Command10" >/dev/null
$ echo "Command11" >/dev/null
$ echo "Command12" >/dev/null

Let’s check the output of the  history command:

$ history
  508  echo "Command4" >/dev/null
  509  echo "Command5" >/dev/null
  510  echo "Command6" >/dev/null
  511  echo "Command7" >/dev/null
  512  echo "Command8" >/dev/null
  513  echo "Command9" >/dev/null
  514  echo "Command10" >/dev/null
  515  echo "Command11" >/dev/null
  516  echo "Command12" >/dev/null
  517  history

As we can observe, the output shows the last 10 commands. This is equal to the value of the HISTSIZE variable.

Let’s now exit gracefully from the current Bash session, re-login again, and verify the output of the history command:

$ history
    1  echo "Command10" >/dev/null
    2  echo "Command11" >/dev/null
    3  echo "Command12" >/dev/null
    4  history
    5  exit

Here, the output contains only the last 5 lines of the previous session. As this example shows, only the last n lines, with n equal to the value of HISTFILESIZE, are written to the disk and are available to the next sessions.

It is important to note we may lose history data due to incompatible values in these environment variables. Hence, we should always choose their values carefully. Those values should be large enough to accommodate the session and overall history.

4. Conclusion

In this tutorial, we discussed the importance of Bash history variables HISTSIZE and HISTFILESIZE, along with their differences.

Authors Bottom

If you have a few years of experience in the Linux ecosystem, and you’re interested in sharing that experience with the community, have a look at our Contribution Guidelines.

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