Watch the filesystem for changes and run the modified file, compiling if necessary.

watch-n-run.sh

#!/bin/bash

# Watch the filesystem for changes and run the modified file, compiling if necessary.
# Requires inotify-tools.
#
# @src https://gist.github.com/duzun/447498b3dbe7967bc91d549f45920d58
# @run https://repl.it/@duzun/watch-n-run
# See also watchnsync() at https://github.com/duzun/dotfiles/blob/7abdde9abcbc558c8c29d418c7cf1dd3ee0cac93/~/.aliasrc#L339

if ! command -v inotifywait >/dev/null; then
    echo >&2 "inotifywait not found"
    echo >&2 "Please install inotify-tools first!"
    exit 1
fi

esc() {
    for i in "$@"; do echo "'$i'"; done
}

main() {

me=$(realpath "$0")
args=("$@")
_PID=

echo "inotifywait ./"
trap "[ -n \"\$_PID\" ] && kill -SIGTERM \$_PID" INT TERM EXIT
while i=($(inotifywait -qre modify --exclude ".git|node_modules|vendor" ./)); do
    set -- "${i[@]}"
    dir=$1
    evt=$2
    shift
    shift
    file="$*"
    fn="$dir$file"
    rfn=$(realpath "$fn")
    ext=${file##*.}
    base=${file%.*}
    [ "$ext" = "$file" ] && ext=
    [ -z "$ext" ] && [ -x "$rfn" ] && continue # skip for executables

    case $ext in
    php) cmd="exec php '$rfn'" ;;
    js) cmd="exec node '$rfn'" ;;
    py) cmd="exec python '$rfn'" ;;
    sh) cmd="exec '$rfn'" ;;
    go) cmd="exec go run '$dir'/*.go" ;;
    c)
        if [ -z "$CC" ]; then
            if command -v clang >/dev/null; then
                CC='clang'
            else
                CC='gcc'
            fi
            echo "CC=$CC"
        fi
        cmd="$CC '$rfn' -o '$base' && exec './$base'"
        ;;

    cpp | C)
        if [ -z "$CXX" ]; then
            # https://medium.com/@alitech_2017/gcc-vs-clang-llvm-an-in-depth-comparison-of-c-c-compilers-899ede2be378
            if command -v clang++ >/dev/null; then
                CXX='clang++'
            else
                CXX='g++'
            fi
            echo "CXX=$CXX"
        fi

        # If this is a project folder with main.cpp file
        if ! grep -q ' main(' "$rfn" && [ -s "${dir}main.$ext" ]; then
            rfn=$(realpath "${dir}main.$ext")
            base=main
        fi
        cmd="$CXX -g '$rfn' -o '$base' && exec './$base'"
        ;;

    java)
        cmd="exec java '$rfn'"
        ;;

    fl)
        echo $rfn
        cmd="exec festival --tts '$rfn'"
        ;;
    *) cmd= ;;
    esac

    [ -z "$cmd" ] && continue # unknown file extension

    clear
    # echo "$evt '$fn'";

    # Kill the previous command
    if [ -n "$_PID" ] && kill -0 "$_PID" &>/dev/null; then
        echo -n "Killing $_PID "
        kill -SIGTERM "$_PID" || pkill -P $$
        while kill -0 "$_PID" &>/dev/null; do
            echo -n "."
            sleep 1
        done
        _PID=
        echo " done"
        echo
    fi

    # Re-exec me
    if [ "$me" = "$rfn" ]; then
        sleep 1
        exec "$rfn" "${args[@]}"
    fi

    _in="$base.in"
    if [ ! -f "$dir$_in" ]; then
        _in=
    else
        _in="< $_in"
    fi

    # Run the command in background
    eargs=($(esc "${args[@]}"))
    (cd "$dir" && eval "$cmd" "${eargs[@]}" "$_in") &

    # Get the PID of the running command and make sure it is running
    _PID=$!
    echo "$evt: Running \`${fn}\`" "${args[@]}" "$_in... PID: $_PID"
    if ! kill -0 "$_PID" &>/dev/null; then
        echo "$_PID not running :("
    fi
done

}

main "$@"