Bash history: "ignoredups" and "erasedups" setting conflict with common history across sessions

First of all, this is not a duplicate of any existing threads on SE. I have read these two threads (1st, 2nd) on better bash history, but none of the answers work – – I am on Fedora 15 by the way.

I added the following to the .bashrc file in the user directory (/home/aahan/), and it doesn’t work. Anyone has a clue?

HISTCONTROL=ignoredups:erasedups  # no duplicate entries
HISTSIZE=1000                     # custom history size
HISTFILESIZE=100000                 # custom history file size
shopt -s histappend                      # append to history, don't overwrite it
PROMPT_COMMAND="history -a; history -c; history -r; $PROMPT_COMMAND"  # Save and reload the history after each command finishes

Okay this is what I want with the bash history (priority):

  • don’t store duplicates, erase any existing ones
  • immediately share history with all open terminals
  • always append history, not overwrite it
  • store multi-line commands as a single command (which is off by default)
  • what’s the default History size and history file size?
Asked By: its_me


In your prompt command, you are using the -c switch. From man bash:

-c   Clear the history list by deleting all the entries

To share your history with all open terminals, you can use -n:

-n   Read the history lines not already read from the history file into the current history list. These are lines appended to the history file since the beginning of the current bash session.

The default size is also in the manual:

The number of commands to remember in the command history (see HISTORY below). The default value is 500.

To save multi-line commands:

The cmdhist shell option, if enabled, causes the shell to attempt to save each line of a multi-line command in the same history entry, adding semicolons where necessary to preserve syntactic correctness. The lithist shell option causes the shell to save the command with embedded newlines instead of semicolons.

Also, you shouldn’t preface HIST* commands with export — they are bash-only variables not environmental variables: HISTCONTROL=ignoredups:erasedups is sufficient.

Answered By: jasonwryan

This is actually a really interesting behavior and I confess I have greatly underestimated the question at the beginning. But first the facts:

1. What works

The functionality can be achieved in several ways, though each works a bit differently. Note that, in each case, to have the history "transferred" to another terminal (updated), one has to press Enter in the terminal, where he/she wants to retrieve the history.

  • option 1:

     shopt -s histappend
     PROMPT_COMMAND="history -a; history -n; $PROMPT_COMMAND"

This has two drawbacks:

  1. At login (opening a terminal), the last command from the history file is read twice into the current terminal’s history buffer;
  2. The buffers of different terminals do not stay in sync with the history file.
  • option 2:

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

(Yes, no need for shopt -s histappend and yes, it has to be history -c in the middle of PROMPT_COMMAND)
This version has also two important drawbacks:

  1. The history file has to be initialized. It has to contain at least one non-empty line (can be anything).
  2. The history command can give false output – see below.

"And the winner is…"

  • option 3:

     shopt -s histappend
     PROMPT_COMMAND="history -n; history -w; history -c; history -r; $PROMPT_COMMAND"

This is as far as it gets. It is the only option to have both erasedups and common history working simultaneously.
This is probably the final solution to all your problems, Aahan.

2. Why does option 2 not seem to work (or: what really doesn’t work as expected)?

As I mentioned, each of the above solutions works differently. But the most misleading interpretation of how the settings work comes from analysing the output of history command. In many cases, the command can give false output. Why? Because it is executed before the sequence of other history commands contained in the PROMPT_COMMAND! However, when using the second or third option, one can monitor the changes of .bash_history contents (using watch -n1 "tail -n20 .bash_history" for example) and see what the real history is.

3. Why option 3 is so complicated?

It all lies in the way erasedups works. As the bash manual states, "(…) erasedups causes all previous lines matching the current line to be removed from the history list before that line is saved". So this is really what the OP wanted (and not just, as I previously thought, to have no duplicates appearing in sequence). Here’s why each of the history -. commands either has to or can not be in the PROMPT_COMMAND:

  • history -n has to be there before history -w to read from .bash_history the commands saved from any other terminal,

  • history -w has to be there in order to save the new history to the file after bash has checked if the command was a duplicate,

  • history -a must not be placed there instead of history -w, because it will add to the file any new command, regardless of whether it was checked as a duplicate.

  • history -c is also needed because it prevents trashing the history buffer after each command,

  • and finally, history -r is needed to restore the history buffer from file, thus finally making the history shared across terminal sessions.

Be aware that this solution will mess up the history order by putting all history from other terminals in front of the newest command entered in the current terminal. It also does not delete duplicate lines already in the history file unless you enter that command again.

Answered By: rozcietrzewiacz

Use this instead:

Answered By: verndog

This is what I came up with and I am happy with it so far…

alias hfix='history -n && history | sort -k2 -k1nr | uniq -f1 | sort -n | cut -c8- > ~/.tmp$$ && history -c && history -r ~/.tmp$$ && history -w && rm ~/.tmp$$'  
shopt -s histappend  
shopt -s extglob  
export HISTIGNORE="!(+(* *))"  


  • Yes, it is complicated… but, it removes all duplicates and yet preserves chronology within each terminal!
  • My HISTIGNORE ignores all commands that don’t have arguments. This may not be desirable by some folks and can be left out.
Answered By: user41176

It does not work, because you forget about:

 -n   read all history lines not already read from the history file
      and append them to the history list

But it seems history -n is just buggy when export HISTCONTROL=ignoreboth:erasedups is in effect.

Lets experiment:

$ export HISTCONTROL=ignoreboth:erasedups
$ export HISTFILE=~/.bash_myhistory
$ HISTIGNORE='history:history -w'
$ history -c
$ history -w

Here we turn on dups erasing, switch history to custom file, clear the history. After all commands complete we have empty history file and one command at current history.

$ history
$ cat ~/.bash_myhistory
$ history
$ 1  [2019-06-17 14:57:19] cat ~/.bash_myhistory

Open second terminal and run those six command too. After that:

$ echo "X"
$ echo "Y"
$ history -w
$ history
  1  [2019-06-17 15:00:21] echo "X"
  2  [2019-06-17 15:00:23] echo "Y"

Now your current history has two commands and history file has:

echo "X"
echo "Y"

Back to first terminal:

$ history -n
$ history
1  [2019-06-17 14:57:19] cat ~/.bash_myhistory 
2  [2019-06-17 15:03:12] history -n

Huh… none of echo commands are read. Switch to second terminal again and:

$ echo "Z"
$ history -w

Now the history file is:

echo "X"
echo "Y"
echo "Z"

Switch to first terminal again:

$ history -n
$ history
  1  [2019-06-17 14:57:19] cat ~/.bash_myhistory 
  2  [2019-06-17 15:03:12] history -n
echo "Z"

You can see that echo "Z" command is merged to history -n.

Another bug is because of commands are read from the history by command number and not by command time, I think. I expect others echo commands appeared at the history

Answered By: Eugen Konkov

erasedups does not trim (like chomp in some languages) the leading and trailing spaces. This is a bug. Also erasedups does not delete all previous entries.

Answered By: Sajith Nallithodi

Using a combination of @rozcietrzewiacz’s option 3 with an exit trap will enable terminals that maintain their own independent history sessions which converge on close. It even seems to work well with multiple sessions across different machines sharing a remote home directory.

export HISTSIZE=5000
export HISTFILESIZE=5000
export HISTCONTROL=ignorespace:erasedups
shopt -s histappend
function historymerge {
    history -n; history -w; history -c; history -r;
trap historymerge EXIT
  • The historymerge function loads out-of-session lines from the history file, combines them with session history, writes out a new history file with deduplication (thus squashing any previously appended duplicate lines), and reloads history.

  • Keeping history -a in the prompt minimizes potential for losing history, as it updates the history file without deduplication on every command.

  • Finally, the trap triggers historymerge on session close for an up-to-date clean history file with the most recently closed session’s commands bubbled to the end of the file (I think).

With this, each terminal session will have its own independent history starting from launch. I find that more useful as I tend to have different terminals open for different tasks (thus am wanting to repeat different commands in each). It’s also mercifully simpler than making sense of multiple terminals constantly trying to re-sync their ordered history in distributed fashion (though you can still do that deliberately using the historymerge function with select sessions or all of them).

Note that you’ll want your size limits to be large enough to hold the desired history length plus the volume of non-deduplicated lines which may be added by all concurrently active sessions. 5000 is sufficient for me largely thanks to the extensive use of HISTIGNORE to filter out spammy low-value commands.

Answered By: HonoredMule

I went with a combination of answers here:

  • I want my history merged at the end, so I used the trap function.
  • I also want my history files separated by hosts so I changed HISTFILE to point to a directory and named files depending on hostname.
  • I added ignorespace option so I can type clear text passwords and not have them show up on the history, e.g.: $ ./.secretfunction -user myuser -password mypassword will not be saved because it starts with space.
  • I added history* and exit to HISTIGNORE just to keep those commands including anything past history like history | grep awesomecommand out of there since I normally wouldnt want it. You can add others like: logout, fg, bg, etc.
  • I then put it all in my ~/.bash_aliases file so it’s not conflicting on upgrades as it has happened sometimes.
shopt -s histappend
function historymerge {
    history -n; history -w; history -c; history -r;
trap historymerge EXIT

Grep your ~/ for PROMPT_COMMAND to make sure you arent already getting it modified with history -a.
I also added the TIME/DATE format HISTTIMEFORMAT="%x %r %Z " I liked but didnt include in the above block since that is locale sensitive.

Answered By: Marlon

In your .bashrc first add:


Then add the following history cleaning helper function (it removes duplicates):

clean_bash_history_file() {
  bash_history_file=$(mktemp "$USER"_bash_historyXXXXXX)
  awk 'NR == FNR { a[$0]++; next; }; ++b[$0] == a[$0]' 
      "$HOME/.bash_history" "$HOME/.bash_history" > "$bash_history_file"
  mv "$bash_history_file" "$HOME/.bash_history"
  unset bash_history_file

Then make the following history update function:

update_history() {   
    history -a
    history -c
    history -r

Finally, add


This will keep the correct history order, and it will remove all duplicates, guaranteed.

It also allows HISTFILESIZE to be larger than HISTSIZE. Just make sure shopt -s histappend is also in your .bashrc

Answered By: Toni Jarjour

I found a lot of solutions either do not handle history timestamps, multi-line history entries, or just leave the history a mess, without any nice ordering.

My solution was to first turn on $HISTTIMEFORMAT (only needs to be set, can be the emtry string if you don’t like seeing the timestamps). And then merge the on-disk ".bash_history" with the in-memory shell ‘history’. Preserving timestamp ordering, and command order within those timestamps.

Optionally removing unique commands (even if multi-line), and/or removing (cleaning out) simple and/or sensitive commands, according to defined perl RE’s. Adjust to suit!

This is the result…

I call this either on demand via and alias (‘hc’ for history clean) and from the ".bash_logout" profile on shell exit.

Adjust as you like to suit your need.


Answered By: anthony

Here’s another combination of the previous answers.

In ~/.bashrc:

shopt -s histappend
function historyclean {
    if [[ -e "$HISTFILE" ]]; then
        exec {history_lock}<"$HISTFILE" && flock -x $history_lock
        history -a
        tac "$HISTFILE" | awk '!x[$0]++' | tac > "$HISTFILE.tmp$$"
        mv -f "$HISTFILE.tmp$$" "$HISTFILE"
        history -c
        history -r
        flock -u $history_lock && unset history_lock
function historymerge {
    history -n; history -w; history -c; history -r; 
trap historymerge EXIT


Compared to previous answers:

  • historymerge() does not remove or prevent duplicates; but it’s useful with trap not to loose history
  • use of /tmp is not secure

Reused ideas: lock file, trap on exit, remove duplicates, merge order. Credits to rozcietrzewiacz, honoredmule, anthony and tony-j.

Answered By: Julien Carsique
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