Share Shell History Across Multiple Terminal Sessions

If you work with multiple terminal tabs or windows—especially in iTerm or Terminal.app—you've probably noticed that each session maintains its own isolated command history. This becomes frustrating when you run a command in one tab and want to recall it in another. By default, bash only saves history when a session closes, and each session can overwrite the others' history.

The Problem

Bash's default behavior creates several issues for multi-tab workflows:

1. Isolated histories: Each terminal session maintains its own separate history in memory
2. Last-write-wins: When sessions close, the last one to exit overwrites the history file
3. Lost commands: Commands from other still-open sessions get lost
4. No real-time sync: You can't access commands from other active sessions

This makes it difficult to "backtrack your steps" when working across multiple terminals, especially during complex debugging or deployment tasks.

The Solution: Synchronized History

You can configure bash to share history across all sessions in real-time by adding a few lines to your shell configuration file.

Configuration

Add this code to your ~/.profile (or ~/.bash_profile or ~/.bashrc):

export HISTCONTROL=ignoredups:erasedups  # no duplicate entries
export HISTSIZE=100000                   # big big history
export HISTFILESIZE=100000               # big big history
shopt -s histappend                      # append to history, don't overwrite it

# Save and reload the history after each command finishes
export PROMPT_COMMAND="history -a; history -c; history -r; $PROMPT_COMMAND"

How It Works

Let's break down each configuration line:

Prevent Duplicates:

export HISTCONTROL=ignoredups:erasedups

Prevents duplicate commands from cluttering your history. The ignoredups option ignores consecutive duplicates, while erasedups removes all previous instances of a command when you run it again.

Increase History Size:

export HISTSIZE=100000
export HISTFILESIZE=100000

By default, bash only keeps 500 commands. These settings increase the in-memory history (HISTSIZE) and the history file (HISTFILESIZE) to 100,000 commands each—enough for months of work.

Append Instead of Overwrite:

shopt -s histappend

Changes bash's behavior to append to the history file instead of overwriting it. This is crucial for preventing sessions from clobbering each other's history.

Real-Time Synchronization:

export PROMPT_COMMAND="history -a; history -c; history -r; $PROMPT_COMMAND"

This is the key to real-time history sharing. The PROMPT_COMMAND runs after every command you execute. It performs three operations:

1. history -a: Appends the current session's new history to the history file
2. history -c: Clears the current session's in-memory history
3. history -r: Reads the entire history file back into memory

This cycle ensures every terminal session always has the complete, up-to-date history from all sessions.

Installation

1. Edit your profile file: bash nano ~/.profile (Or ~/.bash_profile or ~/.bashrc depending on your system)
2. Add the configuration shown above
3. Apply the changes: bash source ~/.profile
4. Test it: Open two terminal tabs, run a unique command in one tab, press Up arrow in the other tab—you should see the command from the first tab.

Benefits

Access Any Command from Any Session: Run ls -la in tab 1, and you can immediately recall it with Up arrow in tab 2.

Never Lose History: Even if a session crashes, all commands are safely written to the history file immediately.

Better Workflow: Jump between tabs freely without worrying about losing track of what you've run.

Huge History: With 100,000 entries, you can search back through months of work.

Notes

Performance: The real-time sync adds minimal overhead. On modern systems, the delay is imperceptible.

Choose the Right File:

• On Mac OS X, use ~/.profile or ~/.bash_profile
• On Linux, use ~/.bashrc
• When in doubt, check which file your system sources by default

History Search: Use Ctrl+R to search through your shared history interactively. With 100,000 entries and all sessions synchronized, this becomes incredibly powerful.

Preserving Existing PROMPT_COMMAND: The configuration appends to $PROMPT_COMMAND (note the $PROMPT_COMMAND at the end), so it won't break any existing prompt customizations.

View the original code on Gist.