Prune Bash History at Login

You can use code based on the following to prune your bash shell command history whenever you log in. This eliminates duplicate commands, which slightly improves performance and can make history easier to use.

I originally described this approach here:

• https://wslguy.net/2021/04/09/clean-up-bash-history-at-shell-startup/

I had tried to modify that to merge history files from multiple machines:

• https://github.com/deliverystack/wslbin/blob/main/bin/.histrc

After moving from WSL (Windows Subsystem for Linux) to Fedora, something wasn't working correctly, and I no longer needed history from multiple machines, so I had gemeni make some suggestions.

You can add these commands directly to ~/.bashrc or a script that it sources, or you can update one of those files to source this script, which you can keep as a separate script to source (not execute - HISTFILE might be different and history -r should run in the current shell).

• histappend: Appended to rather than overwriting HISTFILE on shell exit.
• HISTCONTROL: Don't store sequential duplicates or those that start with a space.
• HISTSIZE: Maximum entries in memory.
• HISTFILESIZE: Maximum number of lines in HISTFILE.
• HISTFILE: Because it's not set yet otherwise.

This is how it works:

• nl: Prepend line number for sorting back to original order.
• First sort: Sort in reverse (newest commands first).
• First sed: Trim whitespace for matching duplicates.
• Second sort: Deduplicate commands.
• Third sort: Re sort to chronological order (most recent last).
• cut: Remove line numbers added by nl.
• Second sed: Trim whitespace, removing any with less than 8 characters.

The hb uses bat to view the history with some formatting.

• https://github.com/sharkdp/bat

shopt -s histappend

export HISTCONTROL=ignoreboth
export HISTSIZE=10000
export HISTFILESIZE=10000

HISTFILE="$HOME/.bash_history"

if [[ -z "$HISTFILE" || ! -f "$HISTFILE" ]]; then
    echo "Error: HISTFILE is not defined or does not exist. Cannot clean history." >&2
    return 1
fi

temphist=$(mktemp)

nl "$HISTFILE" \
    | sort -f -b -k2 -r \
    | sed 's/[[:blank:]]*$//' \
    | sort -f -b -k2 -r -u \
    | sort -n \
    | cut -c8- \
    | sed 's/^[[:space:]]*//; s/[[:space:]]*$//; /\([^[:space:]]\{1\}.*\)\{8\}/!d' > "$temphist"
mv "$temphist" "$HISTFILE"
history -r
alias hb='history | tac | bat -l sh'