run-from-url

#!/usr/bin/env bash

export PS4='+${BASH_SOURCE}:${LINENO}: ${FUNCNAME[0]:+${FUNCNAME[0]}(): } '

set -e

readonly version=0

function print-help() {
    local -r width=$(($(tput cols) - 2))
    cat <<EOH | fold -s -w $width
Usage: ${0##*/} [-houv] URL FILE [...]
Usage: ${0##*/} -i [-houv] [--] [...]
Runs a local copy of a BASH script fetched from the Internet, caching based on ETag.

WARNING: Do not run scripts from the Internet without close inspection.

With URL and FILE, wrap the rest of the command line, otherwise run in place.

  -h, --help       print help and exit normally
  -i, --inplace    run inplace
  -o, --offline    run local copy, do not update
  -u, --update     update local copy, do not run
  -v, --verbose    print verbose output

If NAME is the script name, caches the ETag for URL in .NAME.etag.

If run inplace and NAME is the script name, the local copy is .NAME and the URL is read from .NAME.url.  Use -- to distinguish flags for this script from flags for the local copy.

Examples:
  ${0##*/} https://github.com/some_one/some_script .some_script -flag arg
  some_script -i -- -flag arg
EOH
}

function print-version() {
    cat <<EOV
${0##*/} $version
This is free and unencumbered software released into the public domain.
For more information, please refer to <http://unlicense.org/>.

Written by B. K. Oxley (binkley).
EOV
}

inplace=false
offline=false
update=false
verbose=false
while getopts :hiouv-: opt; do
    [[ - == "$opt" ]] && opt="${OPTARG%%=*}" OPTARG="${OPTARG#*=}"
    case $opt in
    h | help)
        print-help
        exit 0
        ;;
    i | inplace) inplace=true ;;
    o | offline) offline=true ;;
    u | update) update=true ;;
    v | verbose) verbose=true ;;
    version)
        print-version
        exit 0
        ;;
    :)
        cat <<EOE >&2
${0##*/}: option requires an argument -- '$OPTARG'
Try '${0##*/} --help' for more information.
EOE
        exit 2
        ;;
        ?)
        cat <<EOE >&2
${0##*/}: invalid option -- '$OPTARG'
Try '${0##*/} --help' for more information.
EOE
        exit 2
        ;;

    esac

done

shift $((OPTIND - 1))

if $offline && $update; then
    cat <<EOE >&2
${0##*/}: both -o and -u
Try '${0##*/} --help' for more information.
EOE
    exit 2
fi

name=${0##*/}
if $inplace; then
    pushd "${0%/*}"
    url_file=$PWD/.$name.url
    url="$(<"$url_file")"
    content_file="$PWD/.$name"
    popd
    set -- "$url" "$content_file" "$@"
fi >/dev/null

case $# in
0 | 1)
    cat <<EOE >&2
${0##*/}: missing arguments
Try '${0##*/} --help' for more information.
EOE
    exit 2
    ;;

\
    *)
    url=$1
    case $2 in
    /*) content_file=$2 ;;
    *) content_file=$PWD/$2 ;;
    esac
    readonly url content_file
    ;;
esac
shift 2

if $offline; then
    exec $content_file "$@"
fi

case $name in
.*) etag_file=$(dirname "$content_file")/$name.etag ;;
*) etag_file=$(dirname "$content_file")/.$name.etag ;;
esac
readonly etag_file
[[ -s $etag_file ]] || echo 0 >"$etag_file"
old_etag="$(<"$etag_file")"
readonly old_etag

trap 'rm -rf $tmp_dir' EXIT
tmp_dir="$(mktemp -d 2>/dev/null || mktemp -d -t "${0##*/}")"
tmp_headers_file=$tmp_dir/headers
tmp_content_file=$tmp_dir/content

read -r http_code < <(curl -s -D "$tmp_headers_file" -o "$tmp_content_file" \
    -w '%{http_code}\n' \
    -H "If-None-Match: \"$old_etag\"" \
    "$url")
readonly http_code

readonly no_update=304
readonly updated=200
case $http_code in
"$no_update")
    if $verbose; then
        echo "${0##*/}: no update" >&2
    fi
    rm -rf "$tmp_dir"
    exec $content_file "$@"
    ;;
"$updated") if $verbose; then
    echo "${0##*/}: updated" >&2
fi ;;
*)
    echo "${0##*/}: response $http_code for $url" >&2
    exit 1
    ;;
esac

while read -r header value; do
    [[ etag: == "${header,,}" ]] || continue
    new_etag=${value%$'\r'}
    new_etag=${new_etag#\"}
    new_etag=${new_etag%\"}
    break
done <"$tmp_headers_file"
readonly new_etag

if [[ -z "$new_etag" ]]; then
    echo "$0: no ETag for $url" >&2
    exit 1
fi

mv "$tmp_content_file" "$content_file"
chmod +x "$content_file"
echo "$new_etag" >"$etag_file"

rm -rf "$tmp_dir"
exec $content_file "$@"