Improved 4chan image grabber script

#!/bin/sh
# This is modified from the original at: http://pastebin.com/8zqRpKkY

clear;

DIR="$HOME/Pictures/4ch"; # Base download dir for pictures
DELAY=10; # Number of seconds to wait before checking for new posts
URL="";
THREADS=8;
ARGS=$#;
THIS=`basename $0`;

# Exit codes for wget
WEXITS[0]="No problems occurred.";
WEXITS[1]="Generic error code.";
WEXITS[2]="Parse error -- for instance, when parsing command-line options, the .wgetrc or .netrc …";
WEXITS[3]="File I/O error.";
WEXITS[4]="Network failure.";
WEXITS[5]="SSL verification failure.";
WEXITS[6]="Username/password authentication failure.";
WEXITS[7]="Protocol errors.";
WEXITS[8]="Server issued an error response.";
WEXITS[9]="Unknown error code.";

##
# Checks to see if the input is an integer
# Returns 1 if it is, and a 0 if it isn't
##
is_int ()
{
    expr $1 % 1 &> /dev/null;
    isint=$?;

    if [[ "$isint" -lt "2" ]]; then
        return 1;
    else
        return 0;
    fi
}

##
# Prints out the command help and exits
##
usage ()
{
    tput bold;
    echo "NAME";
    tput sgr0;
    echo "  $THIS -- Download images from a 4chan thread...";
    tput bold;
    echo "SYNPOSIS";
    tput sgr0;
    echo "  $THIS [DEST] [THREADS] [DELAY] <URL>\n";
    tput bold;
    echo "DESCRIPTION";
    tput sgr0;

    # using a variable for the description paragraph to make it easier to format..
    # I hate horozontal scrolling when I code.
    DESC="$THIS will download all images (\"THREADS\" simultaneously) from a post on 4chan at the URL you provide, and save them to \"DEST\", creating new folders as necessary. After it downloads the current images it will wait \"DELAY\" seconds and check for new images. If there are new images, it will grab them.";
    echo "  $DESC" | fmt -s 66 66;

    echo "\n    $THIS will stop when you Ctrl+C or it receives a 404 from 4chan.

    DEFAULTS:
        DEST:    $DIR/<post number>/
        DELAY:   $DELAY
        THREADS: $THREADS\n";

    echo "  NOTES:
        Only URL is required unless you specify [THREADS] at which point you must also specify a [DELAY], and if you specify a [DEST] you also have to specify [THREADS] AND [DELAY]." | fmt -s 66 66;

    tput bold;
    echo "EXAMPLES";
    tput sgr0;

    echo "  Download from URL with default options…
    `basename $0` http://boards.4chan.org/b/res/359372915

    Download from URL with a 15s delay before checking for new images…
    `basename $0` 15 http://boards.4chan.org/b/res/359372915

    Download from URL using 8 threads, with a 15s delay before checking for new images…
    `basename $0` 8 15 http://boards.4chan.org/b/res/359372915

    Download from URL using 8 threads, with a 15s delay before checking for new images. Saves the images in /Users/John/4chan…
    `basename $0` \"/Users/John/4chan\" 8 15 http://boards.4chan.org/b/res/359372915";
    exit 1;
}

##
# Check for the proper number of args, and returns the usage summary if an incorrect number is provided.
##
if [ "$ARGS" -lt 1 ] || [ "$ARGS" -gt 4 ]; then
    usage;
fi

##
# Set the correct arg to the correct var based on # of args provided…
##
if [ "$ARGS" -eq 1 ]; then
    URL="$1";
elif [ "$ARGS" -eq 2 ]; then
    URL="$2";
    DELAY="$1";
elif [ "$ARGS" -eq 3 ]; then
    URL="$3";
    DELAY="$2";
    THREADS="$1";
elif [ "$ARGS" -eq 4 ]; then
    URL="$4";
    DELAY="$3";
    THREADS="$2";
    DIR="$1";
else
    usage;
fi


`is_int $DELAY`;
delint=$?;

`is_int $THREADS`;
thrint=$?;

if [[ "$delint" -ne "1" ]] || [[ "$thrint" -ne "1" ]]; then
    echo "\nDELAY and THREADS must both be integers!\n";
    usage;
fi

##
# Don't want no negative delays…
##
if [ "$DELAY" -lt 0 ]; then
    DELAY=0;
fi

##
# Want at least one thread right?
##
if [ "$THREADS" -lt 1 ]; then
    THREADS=1;
fi

SUBDIR=$( echo "$URL" | egrep -o '([0-9]*)$' | sed 's/\.html//g' );
LOC="$DIR/$SUBDIR";
LOGFILE="$LOC/log.txt";


if [ ! -d $LOC ]; then
        mkdir -p $LOC;
fi

cd $LOC;

while [ true ]; do

    # Fuck you clutter!
    clear;

    # Lets show some user-friendly info
    echo "4Chan Image Downloader

URL:     $URL
DELAY:   $DELAY
THREADS: $THREADS
DEST:    $LOC


I'll download all images ($THREADS at a time) from $URL and save them to $LOC.
I'll pause for $DELAY seconds before checking for new images.
I'll stop when I see a CTRL+C from you, or a 404 from 4Chan.\n\n";

        TMP=`mktemp /tmp/4chan.XXXXXX`; # Holds the webpage
        TMP2=`mktemp /tmp/4chanm.XXXXXX`; # Holds the links to all the images in the post
        TMP3=`mktemp /tmp/4chanc.XXXXXX`; # Holds the links to all the images you DON'T have
        WGET_CMD="wget -nv -nc -a $LOGFILE"; # holds the command+args for the 2nd wget, to pull an image

        echo "Grabbing the post at: $URL\n";
        wget -q -O "$TMP" "$URL";
        WEXIT=$?; # so we can check the exit status of wget for that 404

        # testing for an error from wget
        if [ $WEXIT -ne 0 ]; then

            # remove the temp files we created
            rm $TMP $TMP2;

            # wget exits with an 8 if the server
            # sent an error response code .. like a 404 maybe? ;-)
            if [ $WEXIT -eq 8 ]
                then
                    echo "There's that 404 we're waiting for ... lets make like a tree and get out of here!";
                else
                    if [ $WEXIT -gt 8 ]; then
                        WEXIT=9;
                    fi
                    echo "Couldn't get it up ... sorry. Here's the error we're exiting with:\nERROR: ${WEXITS[$WEXIT]} ";
            fi

            exit $WEXIT;
        fi

        ##
        # Strip all the unique image URLs from the page and put them in TMP2
        ##
        egrep 'http://images.4chan.org/[a-z0-9]+/src/([0-9]*).(jpg|jpeg|png|gif)' "$TMP" -o | uniq > "$TMP2";

        ##
        # Check to see which ones are already downloaded and put "new" ones in TMP3
        ##
        echo "Looking at the images you have .. fap fap fap..\n";
        for file in `cat $TMP2`
        do
          fpath="$LOC/`echo $file | egrep -o '([0-9]*).(jpg|jpeg|png|gif)'`";

          if [ ! -e "$fpath" ]; then
            echo $file >> "$TMP3";
          fi

        done

        totalImages=`cat $TMP2 | wc -l | tr -d ' '`;
        newImages=`cat $TMP3 | wc -l | tr -d ' '`;
        imageDiff=$(( totalImages - newImages ));

        echo "You have $imageDiff of $totalImages images in this post.";
        if [[ "$newImages" -gt "0" ]]; then
            echo "Downloading $newImages images...";
            cat $TMP3 | xargs -P $THREADS -I _URL_ $WGET_CMD _URL_;
            SAVED=`cat $LOGFILE | wc -l | tr -d ' '`;
            echo "($SAVED/$newImages) images were successfully saved.\n";
            rm $LOGFILE;
        else
            echo "There are no new images to download.\n";
        fi

        fapTime=3;

        if (( ("$DELAY" - "$fapTime") < 0 )); then
            realFaptime=0;
            fapTime="$DELAY";
        else
            realFaptime=$(( DELAY - fapTime ));
        fi

        echo "I'm going to fap to those images.\nDon't worry, it only takes me $realFaptime seconds.\n";
        sleep $realFaptime;
        echo "Ahhhh… Hold on; lemme clean up my mess.";

        rm $TMP $TMP2 $TMP3;
        sleep $fapTime;
done;