How to Change Bash History Completion to Complete What's Already on the Line

How do I change bash history completion to complete what's already on the line?

Probably something like

# ~/.inputrc
"\e[A": history-search-backward
"\e[B": history-search-forward

or equivalently,

# ~/.bashrc
if [[ $- == *i* ]]
then
    bind '"\e[A": history-search-backward'
    bind '"\e[B": history-search-forward'
fi

(the if statement checks for interactive mode)

Normally, Up and Down are bound to the Readline functions previous-history and next-history respectively. I prefer to bind PgUp/PgDn to these functions, instead of displacing the normal operation of Up/Down.

# ~/.inputrc
"\e[5~": history-search-backward
"\e[6~": history-search-forward

After you modify ~/.inputrc, restart your shell or use Ctrl+X, Ctrl+R to tell it to re-read ~/.inputrc.

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By the way, if you're looking for relevant documentation:

Bash uses The GNU Readline Library for the shell prompt and history.

Bash complete function - Separating completion parts with character other than space

Here's a draft example:

_python_target()
{
    local cmd=$1 cur=$2 pre=$3

    if [[ $pre != -m ]]; then
        return
    fi

    local cur_slash=${cur//./\/}
    local i arr arr2

    arr=( $( compgen -f "$cur_slash" ) )
    arr2=()
    for i in "${arr[@]}"; do
        if [[ -d $i ]]; then
            arr2+=( "$i/" )
        elif [[ $i == *.py ]]; then
            arr2+=( "${i%.py}" )
        fi
    done
    arr2=( "${arr2[@]//\//.}" )

    COMPREPLY=( $( compgen -W "${arr2[*]}" -- "$cur" ) )
}

complete -o nospace -F _python_target python

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Try with the python-2.7.18 source code directory:

Bash history expansion with tab completion

The conceptual terms you're looking for is [command] history and history expansion - if you run man bash, you'll find sections HISTORY and HISTORY EXPANSION devoted to this topic.

That said, in this particular case, it is not history expansion, but the special shell variable $_ that is your friend:

It expands to the last (expanded) argument of the most recent command.

Try the following, which mimics your scenario:

ls "$HOME"  

# Type this on the command line and press TAB (possibly twice)
# _before_ submitting to TAB-complete to matching files in "$HOME"
# (irrespective of what the current directory is).
# $_ at this point contains whatever "$HOME" expanded to, e.g. "/Users/jdoe".
cp $_/  

Note: Whether tab-completion works for a given command is unrelated to whether $_ is used or not. See man bash, section Programmable Completion, for how to manually enable tab-completion for commands of interest.

Preserve bash history in multiple terminal windows

Add the following to your ~/.bashrc:

# Avoid duplicates
HISTCONTROL=ignoredups:erasedups
# When the shell exits, append to the history file instead of overwriting it
shopt -s histappend

# After each command, append to the history file and reread it
PROMPT_COMMAND="${PROMPT_COMMAND:+$PROMPT_COMMAND$'\n'}history -a; history -c; history -r"

Bash command history is not written when a window is closed

You need to leave the shell by typing exit or Ctrl+d rather than just closing the window. exit will write the history implicitly, you can explicitly trigger a history write with history -w at any time.

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