ZSH – output whole history

You've probably got INC_APPEND_HISTORY set.

The INC_APPEND_HISTORY option, from man zshoptions:

This options works like APPEND_HISTORY except that new history lines are added to the $HISTFILE incrementally (as soon as they are entered), rather than waiting until the shell exits.

The option that you want is APPEND_HISTORY:

APPEND_HISTORY If this is set, zsh sessions will append their history list to the history file, rather than replace it. Thus, multiple parallel zsh sessions will all have the new entries from their history lists added to the history file, in the order that they exit. The file will still be periodically re-written to trim it when the number of lines grows 20% beyond the value specified by $SAVEHIST (see also the HIST SAVE BY COPY option).

You can read about these options in the man zshoptions, man zshall or online here.

To set them, in your ~/.zshrc or similar, you should have:

setopt APPEND_HISTORY

Be aware that, if you're using oh-my-zsh by default, I believe, INC_APPEND_HISTORY is used. I'm not 100% sure which way around things get loaded, but if the oh-my-zsh option overrides the one you've set in ~/.zshrc, you can fiddle with it in ~/.oh-my-zsh/lib/history.zsh

The simple answer to your question is you need to set share_history, you do that with:

setopt share_history

Since you obviously did that already (and that option actually works). I suggest you to check:

• whether both shells have the option set;
• whether you are not typing commands with a leading space (since histignorespace makes those be ignored)
• Do you have $HISTFILE set to the same value in all shells?
• whether you are actually saving any history? Say, if you issue echo 123 in tab-1. Go to tab-2, call history. Is it there? (as per your problem, not). Now issue, fc -R (means re-read the history file), and then history is it there now? If not, you may also want to call fc -A (-A will forcefully append your history the file) at tab-1 to make sure history is written to the file.