Helpful Resources

• Where I learned about fc -p (read in and replace) and fc -A (Append)
  • https://unix.stackexchange.com/questions/391181/freezing-the-history-file-temporarily

WARNING: using fc -p will replace your current history file with a blank one. Tread carefully.

GOAL: merge (or concat or join or append) a set of old zsh_history files into a single one.

Imagine you have 3 zsh history files, with timestamps from oldest to newest: zsh_history0, zsh_history1, zsh_history2.

The approach here is to

1. Append zsh_history1 to zsh_history0
2. Append zsh_history2 to zsh_history0 (which will now also contain zsh_history1 data)
3. Replace ~/.zsh_history with combined zsh_history0

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I'll note that I don't actually know what I'm doing. The following two approaches appeared to work?

OPTION 1

# first, make a copy of zsh_history0
cp zsh_history0 zsh_history_merged

# load in zsh_history1 then append it to zsh_history_merged
fc -p zsh_history1
fc -A zsh_history_merged

# load in zsh_history2 then append it to zsh_history_merged
fc -p zsh_history2
fc -A zsh_history_merged

# replace existing history file ($HISTFILE)
cp zsh_history_merged $HISTFILE

OPTION 2

# load in zsh_history0
fc -p zsh_history0

# read in additional files
fc -I -R zsh_history1
fc -I -R zsh_history2

# write the files to zsh_history_merged
fc -W zsh_history_merged

# replace existing history file ($HISTFILE)
cp zsh_history_merged $HISTFILE