Reassemble arguments (support-most-cases implementation) in POSIX shell - Transforming "$*" into "$@"

reassemble_arguments.sh

#!/bin/sh
# SPDX-License-Identifier: MIT

## Copyright (C) 2016 Przemyslaw Pawelczyk <przemoc@gmail.com>
##
## This script is licensed under the terms of the MIT license.
## https://opensource.org/licenses/MIT

# Reassemble arguments (support-most-cases implementation)

ARGC=$#
argcon=
argkey=
argval=
while [ $ARGC -gt 0 ]; do
	arg=$1
	shift
	ARGC=$((ARGC - 1))
	case "$arg" in
	'"'*'"')
		if [ "$argcon" = "'" ]; then
			argval="$argval $arg"
		elif [ "$argcon" = '"' ]; then
			echo "$0: Unsupported syntax!" >&2
		else
			arg=${arg#\"}
			arg=${arg%\"}
			set -- "$@" "$arg"
		fi
		;;
	"'"*"'")
		if [ "$argcon" = '"' ]; then
			argval="$argval $arg"
		elif [ "$argcon" = "'" ]; then
			echo "$0: Unsupported syntax!" >&2
		else
			arg=${arg#\'}
			arg=${arg%\'}
			set -- "$@" "$arg"
		fi
		;;
	'"'|"'")
		if [ -n "$argcon" ]; then
			if [ "$argcon" = "$arg" ]; then
				argval="$argval ${arg%$argcon}"
				set -- "$@" "$argkey$argval"
				argcon=
				argkey=
				argval=
			else
				argval="$argval $arg"
			fi
		else
			argcon=$arg
			argkey=
			argval=
		fi
		;;
	'"'*)
		if [ "$argcon" = "'" ]; then
			if [ "${arg%$argcon}" != "$arg" ] && [ "${arg%$argcon}" = "${arg%%$argcon*}" ]; then
				argval="$argval ${arg%$argcon}"
				set -- "$@" "$argkey$argval"
				argcon=
				argkey=
				argval=
			else
				argval="$argval $arg"
			fi
		elif [ "$argcon" = '"' ]; then
			echo "$0: Unsupported syntax!" >&2
		else
			argcon='"'
			argkey=
			argval=${arg#\"}
		fi
		;;
	"'"*)
		if [ "$argcon" = '"' ]; then
			if [ "${arg%$argcon}" != "$arg" ] && [ "${arg%$argcon}" = "${arg%%$argcon*}" ]; then
				argval="$argval ${arg%$argcon}"
				set -- "$@" "$argkey$argval"
				argcon=
				argkey=
				argval=
			else
				argval="$argval $arg"
			fi
		elif [ "$argcon" = "'" ]; then
			echo "$0: Unsupported syntax!" >&2
		else
			argcon="'"
			argkey=
			argval=${arg#\'}
		fi
		;;
	*=*)
		if [ -n "$argcon" ]; then
			if [ "${arg%$argcon}" != "$arg" ] && [ "${arg%$argcon}" = "${arg%%$argcon*}" ]; then
				argval="$argval ${arg%$argcon}"
				set -- "$@" "$argkey$argval"
				argcon=
				argkey=
				argval=
			else
				argval="$argval $arg"
			fi
		else
			argkey="${arg%%=*}="
			argval=${arg#*=}
			case "$argval" in
			'"'*'"')
				argval=${argval#\"}
				argval=${argval%\"}
				set -- "$@" "$argkey$argval"
				;;
			"'"*"'")
				argval=${argval#\'}
				argval=${argval%\'}
				set -- "$@" "$argkey$argval"
				;;
			'"'*)
				argcon='"'
				argval=${argval#\"}
				;;
			"'"*)
				argcon="'"
				argval=${argval#\'}
				;;
			*)
				set -- "$@" "$argkey$argval"
				;;
			esac
		fi
		;;
	*)
		if [ -n "$argcon" ]; then
			if [ "${arg%$argcon}" != "$arg" ] && [ "${arg%$argcon}" = "${arg%%$argcon*}" ]; then
				argval="$argval ${arg%$argcon}"
				set -- "$@" "$argkey$argval"
				argcon=
				argkey=
				argval=
			else
				argval="$argval $arg"
			fi
		else
			set -- "$@" "$arg"
		fi
		;;
	esac
done
if [ -n "$argcon" ]; then
	set -- "$@" "$argkey$argval"
	echo "$0: Unsupported syntax!" >&2
fi

# show current arguments

for I in "$@"; do
	echo ">$I<"
done

Example:

$ ./reassemble_arguments.sh "test '1" 'test "2' test3="3 three" test4='4 four' test5="f i='v' e" test6='s "i" x' test7="  " '  test8  '
>test '1<
>test "2<
>test3=3 three<
>test4=4 four<
>test5=f i='v' e<
>test6=s "i" x<
>test7=  <
>  test8  <

$ cat arguments
"test '1" 'test "2' test3="3 three" test4='4 four' test5="f i='v' e" test6='s "i" x' test7="  " '  test8  '

$ ./reassemble_arguments.sh $(cat arguments)
>test '1<
>test "2<
>test3=3 three<
>test4=4 four<
>test5=f i='v' e<
>test6=s "i" x<
>test7= <
> test8 <

commit 28b3b793a64001fecd8cd5165661b40147199e36
Author: Przemyslaw Pawelczyk <przemoc@gmail.com>
Date:   2018-02-06 15:04:02 +0100

    reassemble_arguments.sh: Add copyright notice and MIT license notice.

commit b35b2001da0e8b22ea8b15ad7dc33754680737fb
Author: Przemyslaw Pawelczyk <przemoc@gmail.com>
Date:   2018-02-06 15:04:29 +0100

    Add SPDX License Identifier.

    The Software Package Data Exchange (SPDX) is a good initiative, it has
    matured over time and deserves accelerated adoption in open-source.

    https://spdx.org/learn
    https://spdx.org/using-spdx
    https://spdx.org/license-list