Local copy of rust script example from Mahmoud Al-Qudsi blog post https://neosmart.net/blog/self-compiling-rust-code/

rust-script.sh

#!/bin/sh
#![allow()] /*

# rust self-compiler by Mahmoud Al-Qudsi, Copyright NeoSmart Technologies 2020
# See <https://neosmart.net/blog/self-compiling-rust-code/> for info & updates.
#
# This code is freely released to the public domain. In case a public domain
# license is insufficient for your legal department, this code is also licensed
# under the MIT license.

# Get an output path that is derived from the complete path to this self script.
# - `realpath` makes sure if you have two separate `script.rs` files in two
#   different directories, they get mapped to different binaries.
# - `which` makes that work even if you store this script in $PATH and execute
#   it by its filename alone.
# - `cut` is used to print only the hash and not the filename, which `md5sum`
#   always includes in its output.
OUT=/tmp/$(printf "%s" $(realpath $(which "$0")) | md5sum | cut -d' '  -f1)

# Calculate hash of the current contents of the script, so we can avoid
# recompiling if it hasn't changed.
MD5=$(md5sum "$0" | cut -d' '  -f1)

# Check if we have a previously compiled output for this exact source code.
if !(test -f "${OUT}.md5" && test "${MD5}" = "$(cat ${OUT}.md5)"); then
	# The script has been modified or is otherwise not cached.
	# Check if the script already contains an `fn main()` entry point.
	if grep -Eq '^\s*(\[.*?\])*\s*fn\s*main\b*' "$0"; then
		# Compile the input script as-is to the previously determined location.
		rustc "$0" -o ${OUT}
		# Save rustc's exit code so we can compare against it later.
		RUSTC_STATUS=$?
	else
		# The script does not contain an `fn main()` entry point, so add one.
		# We don't use `printf 'fn main() { %s }' because the shebang must
		# come at the beginning of the line, and we don't use `tail` to skip
		# it because that would result in incorrect line numbers in any errors
		# reported by rustc, instead we just comment out the shebang but leave
		# it on the same line as `fn main() {`.
		printf "fn main() {//%s\n}" "$(cat $0)" | rustc - -o ${OUT}
		# Save rustc's exit code so we can compare against it later.
		RUSTC_STATUS=$?
	fi

	# Check if we compiled the script OK, or exit bubbling up the return code.
	if test "${RUSTC_STATUS}" -ne 0; then
		exit ${RUSTC_STATUS}
	fi

	# Save the MD5 of the current version of the script so we can compare
	# against it next time.
	printf "%s" ${MD5} > ${OUT}.md5
fi

# Execute the compiled output. This also ends execution of the shell script,
# as it actually replaces its process with ours; see exec(3) for more on this.
exec ${OUT} $@

# At this point, it's OK to write raw rust code as the shell interpreter
# never gets this far. But we're actually still in the rust comment we opened
# on line 2, so close that: */


fn main() {
    let name = std::env::args().skip(1).next().unwrap_or("world".into());
    println!("Hello, {}!", name);
}