Batch Downloader in Termux in Android

clk android adb install com.termux com.termux.api

pkg install termux-api

set -o errexit # -e
set -o errtrace # -E
set -o nounset # -u
set -o pipefail
shopt -s inherit_errexit

TMP="$(mktemp -d)"
trap "rm -rf '${TMP}'" 0

clk_popline ( ) {
    local file="$1"
    local variable="$2"
    if ! [ -s "${file}" ]
    then
        return 1
    fi
    local thehead="$(head -1 "${file}")"
    (
        # use a subshell to deal with a temp file
        TMPDIR="$(mktemp -d)"
        trap "rm -rf '${TMPDIR}'" 0
        tail +2 "${file}" > "${TMPDIR}/temp"
        mv "${TMPDIR}/temp" "${file}"
    )
    read "$2" < <(echo "${thehead}")
}

lock="${HOME}/multidownloader.lock"
indexfile="${TMP}/index.txt"
tempdldir="${TMP}/dl"

multidownloaderstate="${HOME}/multidownloader"
indexfilehash="${multidownloaderstate}/indexfilehash"
success="${multidownloaderstate}/success"
errors="${multidownloaderstate}/errors"

dest="${HOME}/storage/downloads"

log () {
    local msg="$1"
    echo "$(date): ${msg}"
    termux-notification --title 'Download status' --content "${msg}" --id downloader
}


(
    clean () {
        rm -f "${lock}"
        termux-wake-unlock
    }
    cleanerror () {
        clean
        log "Something went wrong, try running me again"
    }

    if test -e "${lock}"
    then
        log "Already an ongoing process"
        exit
    else
        touch "${lock}"
    fi

    trap "cleanerror" "0"
    termux-wake-lock

    curl --fail --silent --show-error --location "${index}" > "${indexfile}"

    hash="$(sha256sum < "${indexfile}")"
    if ! test -e "${indexfilehash}" || test "${hash}" != "$(cat "${indexfilehash}")"
    then
        rm -rf "${multidownloaderstate}"
        mkdir -p "${multidownloaderstate}"
        echo "${hash}" > "${indexfilehash}"
        touch "${success}"
        touch "${errors}"
    fi

    total="$(cat "${indexfile}"|wc -l)"
    i=0

    log "starting"

    dlit () {
        curl --fail --silent --show-error --location --remote-header-name --remote-name "${url}" --output-dir "${tempdldir}"
        filenames=($(ls "${tempdldir}/"))
        mv "${tempdldir}/"* "${dest}/"
        for filename in "${filenames[@]}"
        do
            termux-media-scan "${dest}/${filename}"
        done
    }

    mkdir -p "${tempdldir}"
    while clk_popline "${indexfile}" url
    do
        if ! grep -q "${url}" "${success}"
        then
            if dlit "${url}"
            then
                echo "${url}" >> "${success}"
            else
                echo "${url}" >> "${errors}"
            fi
        fi
        i=$((i+1))
        log "${i}/${total}"
    done

    log "done"
    trap "clean" "0"
)