Minimal container images often ship without curl, wget, or any HTTP client at all. Bash can open a TCP socket through /dev/tcp, which is enough to write a tiny HTTP/1.1 request by hand for quick checks.

Bash strict mode.

set -euxo pipefail

The -x is sometimes not needed, it prints out every input back. So, this is an option:

set -euo pipefail

This is Greg's (also known as GreyCat's) wiki. It has some pages which may be of interest for people doing Unix shell scripting or system administration.

All Bash quirks are here.