watch a folder for an inotify event and run a command

hotfolder.sh

#!/bin/bash
#-----------------------------------------------------------
# Copyright (C) 2015 GRUBERND http://grubernd.at
# released under a FreeBSD License
#
# watch a folder for an inotify event and run a command
# dependencies: inotify-tools

#--------------------------------------- Defaults
readonly version_hotfolder="15.06"
readonly this_program=$(basename $0)
readonly arguments="$@"
readonly default_settingsfilename="hot_settings"

#--------------------------------------- Help
help_short () {
# short version of help for the short -h argument

cat << 'HELPEND'
. . . Usage: hotfolder  [-h | --help]
                        [-c | --create] [settingsfilename]
                        [-s | --settings <settingsfile>]>
      filename of <settingsfile> can not contain stringbreaking whitespace!
HELPEND
}

help_long () {
# long version of help for the long --help argument

cat << 'HELPEND'
. . . Usage: hotfolder  [-h | --help]
                        [-c | --create] [settingsfilename]
                        [-s | --settings <settingsfile>]>

    -c | --create :: write a new default settingsfile, optional filename
    
    -s | --settings :: run with settings from file

    beware: filename <settingsfile> can not contain stringbreaking whitespace!

    hotfolder watches for events in a folder and then executes a command.

    all settings and the command are contained in a settingsfile.
    if no such file is at hand it can be written by the script and
    then should be edited to suite the job.

    in the settingsfile there is a function command_block() which
    should contain everything that should be done upon an event.

    the variables in the settingsfile control the behaviour:
    - watched_event sets the type of event that is being waited for.
      please see "man inotifywait" for more details about events.
    - watched_folder is the folder being watched recursively.
      can be relative or absolute path.
      important: ~/ will not be expanded. use $HOME/ instead.
    - inotify_format sets what info gets send back to the command_block.
    - hot_command sets the action taken. should not need adjustment.

HELPEND
}

# --------------------------------------
create_settingsfile () {
# to keep the script 100% selfcontained we have the option to create
# a default settingsfile from itself.

if [[ ! -f "$1" ]]; then
echo -e "writing hotfolder settingsfile with defaults: $1"

cat > "$1" << 'CREATEEND'
#!/bin/bash
# hotfolder settings file
command_block () {
    # here goes everything you want to happen upon an event:
    echo -e "argument 1    :: $1"
    echo -e "argument 2    :: $2"
}
# various argument parts passed on, see "man inotifywait" for more details
watched_event="close_write"
watched_folder="$HOME/pictures/screenshots/"    # do NOT use ~/
inotify_format="%w %f"
hot_command="command_block"
CREATEEND

else
    echo -e "create ERROR: file already exists"
fi
}

# --------------------------------------
parse_arguments () {
    # depending on arguments we run functions
    # only correct args for -s|--settings keep the script on running
    # all other cases stop the script after their action

    # without arguments display a little help and stop
    if [[ -z "$@" ]]; then
        echo -e "hotfolder: missing arguments."
        help_short
        exit 1
    fi

    # work through the arguments 
    local i=
    for i in "$@"; do
    case $i in
        -h)     help_short
                exit
                ;;
        --help) help_long
                exit
                ;;
        -c | --create)
                if [[ -n "$2" ]]; then
                    settingsfile="$2"
                    create_settingsfile "$2"
                else
                    create_settingsfile "$default_settingsfilename"
                fi
                exit
                ;;
        -s | --settings)
                if [[ -n "$2" ]]; then
                    settingsfile="$2"
                    shift 2
                    continue
                else
                    echo -e "ERROR: missing argument for settingsfile"
                    exit 1
                fi
                ;;
        *)
            break
            ;;
    esac
    done
}

# --------------------------------------
get_settings () {
    # include the settingsfile as part of the script or break on error

    if [[ -f "$settingsfile" ]]; then
        source "$settingsfile"
    else
        echo -e "settingsfile ERROR: $settingsfile is not a file."
        exit 1
    fi
}

check_settings () {
    # break on various errors with helpful error messages
    # those provided by inotifywait are somewhat cryptic

    if [[ -z "$watched_event" ]]; then
        echo -e "settingsfile ERROR: watched_event is not set"
        exit 1
    fi
    if [[ ! -d "$watched_folder" ]]; then
        echo -e "settingsfile ERROR: $watched_folder is not a folder"
        exit 1
    fi
    if [[ -z "$hot_command" ]]; then
        echo -e "settingsfile ERROR: hot_command is not set"
        exit 1
    fi
}

# --------------------------------------
inotify_loop () {
    # this is where the real work happens
    # if variables are replaced with actual values this works as a oneliner
    # the rest of the script is just to help with the workflow
    # TODO ?? put all arguments for inotifywait into the settingsfile ??

    inotifywait --event "$watched_event" \
                --monitor \
                --recursive \
                --quiet \
                --format "$inotify_format" \
                "$watched_folder" \
    | while read this
        do
            # $this is NOT quoted so multiple params can be passed
            $hot_command $this
        done
}

# ---------------------------------------------------------- Main
# most arguments cause the script to stop somewhere in parse_arguments
# also get_ and check_settings contain conditional breakpoints

parse_arguments $arguments

get_settings
check_settings

echo -e "hotfolder - GRUBERND $version_hotfolder :: $settingsfile"
echo -e "press Ctrl-C to end.."

inotify_loop 

# EOF