Run as Administrator from WSL

.runas

#!/bin/bash
#
# == SUMMARY ===================================================================
#
#  This script is used to invoke a native Windows program (.exe) or batch script
#  (.bat, .cmd, .com) —  referred to as COMMAND below — as an Administrator.
#
#  It is intended to be used from a WSL shell session, where the target program
#  runs in the parent Windows environment with elevated privileges.
#
#  You can then reuse this shell script as a common mechanism for running 
#  frequently-used tools requiring admin rights. 
#
#  You do not need to copy or modify the script for each tool; 
#  just create a specially-nammed symlink pointing to the script.
#
#  The script will resolve the native command based on the name of the symlink
#  (i.e., argv[0]). Detailed instructions are provided below.
#
#  ----------------------------------------------------------------------------
#
#  There are two different methods for using this script:
#
#  -- Direct --
#
#    This is the simpler method. It allows a user to invoke the target COMMAND
#    directly with command line arguments. It requires two files:
#
#      1. "/a/b/foo/{.,}COMMAND.{exe,bat,cmd,com}"
#        The Windows program/script you wish to run as administrator.
#        This file must be an executable or a symlink to one.
#      2. "/a/b/foo/COMMAND{.*sh}"
#        Symlink pointing to this script. 
#
#      !! Files 1 and 2 must be in the same dir.
#
#  -- Indirect --
#
#    This method allows for some extra processing to occur prior to calling the
#    target COMMAND. It requires three files:
#
#      1. "/a/b/foo/{.,}COMMAND.{exe,bat,cmd,com}"
#        The Windows program/script you wish to run as administrator.
#        This file must be an executable or a symlink to one.
#      2. "/a/b/foo/{.,}COMMAND{.ln,.*sh}"
#        Symlink pointing to this script.
#      3. "/x/y/bar/anything"
#        Script or program that invokes file 2 above with all necessary args.
#
#      !! Files 1 and 2 must be in the same dir.
#
# == NOTES =====================================================================
# 
#  The symlink method, of course, only works on systems that support them, which 
#  ironically excludes the native NTFS file system. Thus, this script depends 
#  on some tool for file path translation (from Unix to Windows).
#
#  For WSL, it uses `wslpath`. Prebuilt binaries and build docs on GitHub:
#   <https://github.com/ardnew/wslpath/>
#
#  On Cygwin, it uses `cygpath`, which comes built-in by default:
#   <https://www.cygwin.com/>.
#
# ==============================================================================

# define is syntactic sugar for assigning HEREDOC content to a variable. 
# Works with quoted content (e.g., define foo <<'EOF' ...), as well as scripts
# that set -e (since read returns non-zero on success).
define() { IFS='\n' read -r -d '' ${1} || true; }

# Print an error message to stderr and exit script with the given status.
# 	halt [STATUS [FORMAT [PARAM...]]]
halt() {
	local ret=${1:-127}
	local pre='error' msg=${2:-'(unspecified)'}
	[[ $ret =~ ^[0-9]*$ ]] ||
		ret=126
	[[ $# -gt 0 && $1 -eq 0 ]] &&
		pre='exit' msg=${2:-'OK'}
	[[ $# -ge 3 ]] &&
		msg=$( printf -- "${2}" "${@:3}" )
	printf -- '%s(%d): %s\n' "${pre}" ${ret} "${msg}" >&2
	exit ${ret}
} 

# Prints all arguments after the first and delimited by the first.
# Prints only the second argument if exactly two arguments given.
# Nothing is printed if fewer than two arguments are given.
joinstr() {
	local d=${1-} f=${2-}
	shift 2 && printf %s "$f" "${@/#/$d}"
}

kerver='/proc/version'

# Test if a given expression (PCRE) is found in the kernel's version string
chkver() { [ "x${1:-}" != x ] && command grep -qiP "${1}" "${kerver}" ; }

unset -v cmd
cmd=${0##*/}
cmd=${cmd%.ln}
cmd=${cmd%.*sh}
cmd=${cmd%.exe}
cmd=${cmd%.bat}

ord=( exe bat cmd com )

# Infer the target program/script path from the caller's file path and convert 
# that to an absolute Windows file path.
unset -v target winpath 
if chkver 'Microsoft'; then
	winpath=( 'wslpath' -w )
elif chkver 'Cygwin'; then
	winpath=( 'cygpath' -l -a -w )
else
	[[ -r "${kerver}" ]] ||
		halt 3 'cannot determine platform: file not found: %s' "${kerver}"
	kerver=$( cat "${kerver}" )
	halt 4 'cannot make Windows path: unknown platform: %s' "${kerver:-'<!NULL>'}"
fi
pathbin=$( type -P "${winpath[0]:-}" ) ||
	halt 5 'required tool not found: %s' "${winpath[0]:-'<!NULL>'}"
winpath[0]=${pathbin}

[[ x${TRACE} != x ]] && set -x

self=${0%/*}
unset -v target targpath
for ext in "${ord[@]}"; do
	while read -re path; do
		targpath=$( realpath -eq "${path}/${cmd}.${ext}" )
		[[ -e "${targpath}" ]] || continue
		if target=$( "${winpath[@]}" "${targpath}" ); then
			[[ -x "${targpath}" ]] ||	chmod +x "${targpath}" ||
				halt 6 'failed to enable execute permissions: %s\n' "${targpath}"
			break
		fi
	# always check CWD "." first, then script dir ${self}, and finally ${PATH}
	done < <( echo ".:${self}:${PATH}" | tr ':' '\n' )
	[[ -z $target ]] || break
done
[[ -n ${target} ]] ||
	halt 7 'target executable not found: %s extensions: %s)' \
		"${target:-'<!NULL>'}" "${ord[*]/#/.}"

# Invoke PowerShell with the "Start-Process" cmdlet and the "runas" start verb,
# forwarding all arguments received.

pshash() {
	perl -e'
		use strict;
		use warnings;
		# double/single quote without escaping
		my ($QQ, $Q) = map {chr} 0x22, 0x27; 
		($_, @_) = @ARGV;
		my $tab = $ENV{indent} || "";
		#@_ = map { qq|"$_"| } @_;
		my @opt = (
			FilePath => $_,
			Verb => q(RunAs),
			Wait => q($true),
#			WindowStyle => q(Hidden),
#			RedirectStandardInput => q("in"),
#			UseNewEnvironment => q($true),
			( @_ > 0 ? ( ArgumentList => qq|@_| ) : () )
		);
		while ($_ = shift @opt) {
			printf "%s%s = %s\n", $tab, $_,
				# enquote unless it begins with a sigil ($), quote, or at-sym (@).
				map { /^\s*[\$${Q}@]/ ? $_ : qq|${Q}$_${Q}| } shift @opt
		}
	' "${@}"
}

define star <<_EOF_
{
	\$Options = @{
$( indent=$'\t\t' pshash "${target}" "$@" )
	}
	Start-Process @Options
	Exit \$LASTEXITCODE
}
_EOF_

exec cat <( powershell.exe -Command "& ${star}" )