Run nim source files like scripts (with tcc and binfmt_misc)

This is a rough guide on how to make nim source files behave like scripts. This document targets debian/ubuntu-likes; you may have to adjust for other systems.

Prequisites

• Install tcc (optional, but recommended): sudo apt install tcc
• Make sure binfmt_misc support is available: ls /proc/sys/fs/binfmt_misc/register

The script runner

Create /usr/local/bin/nimtcc, like so:

#!/bin/bash

if [[ "$#" -eq 0 ]]; then
	echo "at least 1 argument required" >&2
	exit 1
fi

if [[ ! -e "$1" ]]; then
	echo "not found: $1" >&2
	exit 1
fi

umask u+rwx
out=$(mktemp ${TMPDIR:-/tmp/}$(basename $1).XXXXXXXXXXXX)

function finish() {
	rm -- "$out"
}
trap finish EXIT

nim compile \
	--verbosity:0 \
	'--hint[Processing]:off' \
	--cc:tcc \
	"-o:$out" \
	-r $@

The script creates a temp file (in /tmp) to write the compiled program to, and immediately removes it thereafter again.

• Make sure nim is available on PATH, or change the path to the binary in the script.
• Mark it as executable: sudo chmod +x /usr/local/bin/nimtcc
• .. and test it: $ nimtcc my_script.nim. If it doesn't work, fix it.

N.B.:

• This still creates a nimcache in the current directory. I've left it in as a compromise to speed up iterative script development. If this is not desired, you will have to adjust the script to create an additional directory (with mktemp -d), pass that to the compiler; and then remove it afterwards.
• Similarily, you can get rid of the whole mktemp to write the script binary to the current directory.

binfmt_misc

Now, optionally, make it so you can mark scripts as executable and run them directly. This requires binfmt_misc support in your kernel. Most modern kernels have this enabled by default.

• $ echo ':nimtcc:E::nim::/usr/local/bin/nimtcc:' | sudo tee -a /proc/sys/fs/binfmt_misc/register
• $ chmod +x my_script.nim
• $ ./my_script.nim