removes regex pattern from bash history (also deduplicates history file)

purgehistory_core

#!/usr/bin/bash
if [ -z "$lastCMD" ]; then
    if [ -z "$SHELLSTARTED" ]; then
        export SHELLSTARTED="1";
    else
        echo -e "purgehistory_core: Error 1: \$lastCMD is empty";
    fi
    exit 1
elif [ ! -z "$HISTPURGEFAIL" ]; then
    exit 2
fi
#phc_debug=1
lock="/tmp/.lock-historypurge"
exec 31>$lock
flock --timeout 5 31 || exit 1
HISTFILE="/"

# function to free lock and temp files
free_(){
    rm -rf $lock
    rm -rf $tmp_before
    rm -rf $tmp_after
    flock -u 31
    exec 31>&-
}

# function for printing errors
error(){
    case "$1" in
        "2") echo -e "Error 2: purgehistory_core: Critical failue.\nCould not run pcregrep (probably). Will not try again this session."
                 export HISTPURGEFAIL="2"
 ;; "3") echo -e "purgehistory_core: Error 3: $bhistory is empty"
 ;; "4") echo -e "purgehistory_core: Error 4: failed: cp $bhistory $tmp_before\nPerhaps $tmp_before already exists."
 ;; "5") echo -e "purgehistory_core: Error 5: $tmp_before is empty"
 ;; "6") echo -e "purgehistory_core: Error 6: $tmp_after is empty"
 ;; *) echo "Not an error(yet), a typo" ;;
    esac
    free_
    unset -f error
    unset -f free_
    return $(($1))
}

# function for checking if file is empty
isempty(){
    if [[ -f $1 ]]; then
        if [[ -s $1 ]]; then
            if cat $1 2>/dev/null > /tmp/temp_file_prime ; then
                return 1;
            fi
        fi
    fi
    return 0;
}

# the first argument given to this script is the regex to match the history against
if [ -z "$1" ]; then
    core_regex="#\d{10}\s[^#\s].*"
else
    core_regex="#\d{10}\s(?!$1)[^#\s].*"
fi

# debugging prints regex pattern
if [ ! -z "$phc_debug" ]; then
    echo "debugging"
    echo "$core_regex"
fi



# our files
bhistory="$HOME/.bash_history"
tmp_before="/tmp/.hist_before"
tmp_after="/tmp/.hist_after"

# if history is empty
if isempty $bhistory; then
    error 3
    exit 3
fi

# if cp operation fails
if cp $bhistory $tmp_before; then :
else
    error 4
    exit 4
fi

# if file copy is empty
if isempty $tmp_before; then
    error 5
    exit 5
fi

# deduplicate and remove history matching the user provided pattern
if cat $tmp_before | pcre2grep -M "$core_regex" | tac | awk '!seen[$0]++' | tac > $tmp_after; then
    if [ ! -z "$phc_debug" ]; then :
        # do nothing if debugging
    elif isempty $tmp_after; then
        # error if manipulated history is entirely empty
        error 6
        exit 6
    else
        # operation was successful, replace history and reload it
        mv $tmp_after $bhistory
        history -c
        history -r
    fi
else
    # operation failed outright - assumed to be pcre2grep missing from system - error prints once only
    error 2
    exit 2
fi

# free up the lock, and undefine our internal functions
free_
unset -f error
unset -f free_