Automatically generate a config file compatible with LibreSSL

[ghost]

Address issue #76 by generating a config file with the substitutions having been performed by either envsubst from GNU gettext, or Perl, if available.

[TinCanTech]

EasyRSA 3 now supports libressl, so this PR should probably be closed.

[ghost]

The current implementation is unsafe. It would be preferable not to use sed but the options are limited when aiming for portability. Bash would do, but bash isn't sh. The ed utility can't be relied upon because most Linux vendors ignore the fact that it's a standard utility.

Given the use of sed, I would suggest the use of a custom escaping routine at least. Consider the following program.

#!/bin/sh

escape() {
	printf %s "$1" | sed -e 's/\([,&\]\)/\\\1/g'
}

set -- 'foo,bar' 'foo\1bar' 'foo&bar'

echo "Bad method ..."
i=1
for value in "$@"; do
	printf 'Sample %u: ' "$i"
	printf '%s\n' '$SOME_VAR' | sed -e "s,\$SOME_VAR,$value),"
	: $((i += 1))
done

echo "Improved method ..."
i=1
for value in "$@"; do
	printf 'Sample %u: ' "$i"
	printf '%s\n' '$SOME_VAR' | sed -e "s,\$SOME_VAR,$(escape "$value"),"
	: $((i += 1))
done

On my system, the results are as follows:-

Bad method ...
Sample 1: sed: -e expression #1, char 17: unknown option to `s'
Sample 2: sed: -e expression #1, char 22: invalid reference \1 on `s' command's RHS
Sample 3: foo$SOME_VARbar)
Improved method ...
Sample 1: foo,bar
Sample 2: foo\1bar
Sample 3: foo&bar

EDIT: Goofed my own sample code. Fixed.

[TinCanTech]

The current implementation is unsafe

Improvements are welcome in the form of tested PRs.

[ghost]

The problem has been adequately explained; I'm not submitting another PR. I will, however, close this one.