sync local clock in bash without NTP

sync-time.sh

# I want to sync the local clock but don't have access to any NTP server.
# Websites such as https://time.is give me the correct time and I can manually adjust the local clock.

# But then I recall that a HTTP response often contains a date header with current time in GMT timezone.
# I'll use it to set the system clock with the precision of 1 or 2 seconds.

# in Linux
sudo date -us "$(curl -Is google.com | grep '^Date:' | cut -d' ' -f3-)"

# in Linux with fish shell
sudo date -us (curl -Is google.com | grep '^Date:' | cut -d' ' -f3-)

# in MacOS
sudo date -uf "%d %b %Y %T" "$(curl -Is google.com | grep '^Date:' | cut -d' ' -f3-6)"

# in MacOS with fish shell
sudo date -uf "%d %b %Y %T" (curl -Is google.com | grep '^Date:' | cut -d' ' -f3-6)

# If you don't have `curl`, you can use `wget`
wget -Sq --max-redirect=0 google.com | grep '^Date:' | cut -d' ' -f3-6

# You can use another website instead of google.com (if it returns a date header with UTC time).
# WARNING: be careful, some websites have a date header with time in the past.

# Use "time" to measure which one is faster for you.
time curl -Is t.co
time curl -Is a.co
time curl -Is fb.com
time curl -Is c.cc
time curl -Is t.tt
time curl -Is yt.be
time curl -Is g.gl
time curl -Is goo.gl
time curl -Is gogle.com
time curl -Is gooogle.com
time curl -Is googl.com
time curl -Is googlee.com
time curl -Is ggoogle.com
time curl -Is goolge.com
time curl -Is googel.com