Shell script to check and possibly upgrade zoom package under Debian or derivative GNU/Linux distribution

zoom-up

#!/usr/bin/bash

# Check available version and upgrade zoom if possible.

set -f
set -u
set -e

if [ $# != 0 ]; then
    echo "Download and install zoom package. Abort if it does not supersede currently installed version."
    echo "Usage: $0"
    exit 1
fi

arch="$(dpkg --print-architecture)"
echo "info: architecture ${arch}"
deb_name=$(mktemp --tmpdir "zoom_${arch}_XXXXXX.deb")

# Allow other users, including _apt, to read the file, to avoid a warning:
#  N: Download is performed unsandboxed as root as file '/tmp/zoom_amd64_XXXXXX.deb' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
chmod a+r "${deb_name}" || true

# Here we download the file, but as it downloads we examine its header
# to grovel out the version, and if we already have that version the
# download is terminated early. The trick is to put the downloading
# process in the background, and then trickle the file being
# downloaded into a scanning process until enough has been seen to
# extract the version. And then decide what to do.

# Background this process:
curl --fail --silent --show-error --location "https://zoom.us/client/latest/zoom_${arch}.deb" >> "${deb_name}" &

downloadpid=$!

# Figure out currently installed version
v0="$(apt-cache policy zoom | egrep '  Installed: ' | cut --delimiter=: --field=2 | tr -d ' ')"
if [ -n "${v0}" ]; then
    echo "info: current zoom version ${v0}"
else
    echo "info: zoom not currently installed"
fi

# Snuffle through downloading file to extract version:
v="$(dpkg --field <(tail --retry --follow --pid=${downloadpid} --bytes=+0 "${deb_name}" 2>/dev/null) Version)"
echo "info: available zoom version ${v}"

# install downloaded or existing package if appropriate
if dpkg --compare-versions "${v0}" lt "${v}"; then
    echo "info: waiting for download to complete"
    wait -f ${downloadpid} || true
    # This would be a good place to check the integrity of ${deb_name}
    # because an error in the downloading process, like a network fault,
    # could result in a truncated or corrupt file.
    sudo apt install "${deb_name}"
else
    echo "info: aborting download"
    kill ${downloadpid}
    wait -f ${downloadpid} || true
fi

rm -f "${deb_name}"