.bashrc, highlight russian homoglyphs

check_homoglyph_error.sh

# homoglyphs are characters from different writing systems that look identical or nearly identical.
# The Russian (Cyrillic) character "С" and the English (Latin) character "C" are a prime example.
# which means, that if you type something like curl example.сom, where "C" in ".com" is Cyrillic "C" - it will obviously not work

# Function below uses trap to catch those and highlight them
# add it to your .bashrc or .bash_profile

# Enable skipping commands from the DEBUG trap
shopt -s extdebug

# Define the homoglyph characters we want to check for
HOMOGLYPHS_CYR="сСрРаАеЕоОхХНКМТВу"
HOMOGLYPHS_LAT="cCpPaAeEoOxXHKMTBy"

# Reentry guard for the DEBUG trap
__HOMOGLYPH_IN_DEBUG=""

function check_homoglyph_error() {
    # Interactive shells only
    [[ $- != *i* ]] && return 0

    # Prevent recursion
    if [[ -n "$__HOMOGLYPH_IN_DEBUG" ]]; then
        return 0
    fi
    __HOMOGLYPH_IN_DEBUG=1

    local skip=0

    if [[ -n "$BASH_COMMAND" ]]; then
        if echo "$BASH_COMMAND" | tr -d "$HOMOGLYPHS_LAT" | grep -q "[$HOMOGLYPHS_CYR]"; then
            local warning="\n⚠️  HOMOGLYPH DETECTED! ⚠️\n"
            warning+="It looks like you used a Russian (Cyrillic) character.\n"
            printf "%b" "$warning"

            if [[ -t 1 && "$(tput colors 2>/dev/null)" -ge 8 ]]; then
                local red_color no_color highlighted_command
                red_color="$(tput bold; tput setaf 1)"
                no_color="$(tput sgr0)"
                highlighted_command=$(sed -E "s/([${HOMOGLYPHS_CYR}])/${red_color}\1${no_color}/g" <<<"$BASH_COMMAND")
                printf 'Your command: %s\n' "$highlighted_command"
            else
                echo "Your command: $BASH_COMMAND"
                local indicator_line=""
                for (( i=0; i<${#BASH_COMMAND}; i++ )); do
                    local char="${BASH_COMMAND:$i:1}"
                    if [[ "$HOMOGLYPHS_CYR" == *"$char"* ]]; then
                        indicator_line+="^"
                    else
                        indicator_line+=" "
                    fi
                done
                echo "              $indicator_line"
            fi

            # Ask whether to run anyway; default to "No" if no TTY or non‑y answer
            local ans=""
            if [[ -t 1 && -r /dev/tty ]]; then
                read -r -n 1 -p "Run it anyway? [y/N] " ans < /dev/tty
                echo
                [[ "$ans" =~ ^[Yy]$ ]] || skip=1
            else
                skip=1
            fi
        fi
    fi

    __HOMOGLYPH_IN_DEBUG=""

    if (( skip )); then
        # Prevent the command from running (requires extdebug)
        return 1
    fi
    return 0
}

# Run before every command
trap 'check_homoglyph_error' DEBUG