отполировано. вроде

#! /bin/bash

set -e
shopt -s extglob

TEMPFILE= TEMPDIR= DIR=

usage () {
cat <<EOF
This script saves image from cliboard into
a png file which name is sha256sum of that
image.
This script uses xclip and therefore is
valid only for X11 sessions.

Options:
-1          Nothing will work without
            this option. Don't ask why.
-h (--help):        Show this help.
-d (--directory):   Specify target directory.
            Otherwise current is used.
-t (--tempdir):     Set directory for temp file.
-f (--tfile):       Set temporary file name.
EOF
}

validate_and_set_tfile () {
# $1 is tempdir
local files=(
        ".image"
        "._image"
        ".__image"
        ".IMAGE"
        "._IMAGE"
        ".__IMAGE"
        )

for file in "${files[@]}"
do
    if [[ ! -a ${1}/$file ]]
    then
        TEMPFILE="$file"
        return 0
    fi
done
cat <<EOF
Could not set tempfile. Try specifying
it manually. The reason is that all
tried files already exist.
EOF
return 1
}

validate_and_set_tdir () {
local dirs=(
        "/tmp"
        "/tmp/$USER"
        "/tmp/_$USER"
        "/tmp/__$USER"
        )

for dir in "${dirs[@]}"
do
    if [[ -d $dir ]] && touch -c "$dir" &>/dev/null
    then
        TEMPDIR="$dir"
        return 0
    elif mkdir "$dir" &>/dev/null
    then
        TEMPDIR="$dir"
        return 0
    fi
done
cat <<EOF
Could not set tempdir. Try doing it
manually. The reason is that all
tried directories either do not
exist or are inacessible.
EOF
return 1
}

validate_tfile () {
# $1 is tempdir, $2 is tempfile.
if [[ -a ${1}/${2} ]]
then
    echo "File ""${1}/${2}"" exists."
    return 1
fi
return 0
}

validate_dir () {
if [[ -d $1 ]] && touch -c "$1" &>/dev/null
then
    return 0
fi
cat <<EOF
Could not access "$1" or it does not exist.
EOF
return 1
}

if [[ -z $1 || $1 = @(-h|--help) ]]
then
    usage
    exit $(( $# ? 0 : 1 ))
fi

while (( $# ))
do
    case $1 in
        -1)
            GO=1
            shift
            ;;
        -d|--directory)
            DIR="$2"
            shift 2
            ;;
        -t|--tempdir)
            TEMPDIR="$2"
            shift 2
            ;;
        -f|--tfile)
            TEMPFILE="$2"
            shift 2
            ;;
        *)

            echo "Unknown option ""$1"""
            exit 1
            ;;
    esac
done

# Looking if we are ready to go.
if (( ! GO ))
then
    usage
    exit 1
fi

# Setting directory where the resulting file
# will be stored
if [[ -n $DIR ]]
then
    validate_dir "$DIR" ||
        exit $?
else
    DIR="$(pwd)"
fi

# Setting tempdir
if [[ -n $TEMPDIR ]]
then
    validate_dir "$TEMPDIR" ||
        exit $?
else
    validate_and_set_tdir ||
        exit $?
fi

# Setting tempfile
if [[ -n $TEMPFILE ]]
then
    validate_tfile "$TEMPDIR" "$TEMPFILE" ||
        exit $?
else
    validate_and_set_tfile "$TEMPDIR" ||
        exit $?
fi

xclip -selection c -t image/png -o > \
    "${TEMPDIR}/${TEMPFILE}"
sha256sum - <"${TEMPDIR}/${TEMPFILE}" |
    cut -d' ' -f 1 |
    cp -n "${TEMPDIR}/${TEMPFILE}" \
    "${DIR}/$(cat -).png"
rm "${TEMPDIR:?}/${TEMPFILE}"
rmdir "$TEMPDIR" &>/dev/null || true