00-minus-minus-position.md

Once I decided weirdly to combine two commands into a single one with possibility to keep the command line options of the both commands. It was assumed the following:

# original and simple usage
command1 options1 | command2 options2

# modified and weird one
super_command options1 -- options2

Bash supports string and array indexing, whereas a POSIX shell does not. With bash we can use something similar to (assuming that the double dash "--" is on the sixth position):

command1 "${@:1:5}" | command2 "${@:7}"

I found a workaround way for POSIX. It has been tested under BusyBox which provides the restricted and POSIX-compliant ash.

Usage (see the complete proof of the concept below)

minus_minus_position "$@"

eval log_left $( reparse_left_arguments "$@" ) \
| eval log_right $( reparse_right_arguments "$@" )

demo-1

#!/bin/sh

# =========================================================================

. ./minus-minus-position.sh

# =========================================================================

demo() {
	s="$1"
	shift

	printf "$s : %s\n" "$@" >&2
}

# =========================================================================

minus_minus_position "$@"

eval demo "LEFT" $( reparse_left_arguments "$@" ) \
| eval demo "RIGHT" $( reparse_right_arguments "$@" )

# =========================================================================

# EOF

demo-2

#!/bin/sh

# =========================================================================

. ./minus-minus-position.sh

# =========================================================================

demo() {
	s="$1"
	shift

	printf "$s : %s\n" "$@" >&2
}

# =========================================================================

minus_minus_position "$@"

(
	eval set -- $( reparse_left_arguments "$@" )
	demo "LEFT" "$@"
) | (
	eval set -- $( reparse_right_arguments "$@" )
	demo "RIGHT" "$@"
)

# =========================================================================

# EOF

minus-minus-position.sh

# =========================================================================
#
# POSIX-compliant way for string and array indexing
# A partial case implementation for the double minus
#
# =========================================================================

# Look up the position of the "--" option and set the MINUS_MINUS_POSITION
# variable to the position of "--", if it presents in the command line.
# Set to $#+1, otherwise.
minus_minus_position() {
	MINUS_MINUS_POSITION=1

	while [ $# -gt 0 ]
	do
		[ "$1" = "--" ] && return
		shift
		MINUS_MINUS_POSITION=$(( MINUS_MINUS_POSITION+1 ))
	done
}

# Prepare arguments for setting them in "eval ..."
reparse_arguments() {
	[ $# -gt 0 ] || return

	printf '%s\n' "$@" \
	| awk -v apos="'" -v bsol="\\\\" -v ORS=" " \
	-v side="$MINUS_MINUS_SIDE" \
	-v mmpos="$MINUS_MINUS_POSITION" '
	side < 0 && NR == mmpos { exit }
	side > 0 && NR <= mmpos { next }
	{ gsub(apos, apos bsol apos apos); print apos $0 apos }'
}


# Prepare arguments for setting them in "eval ..." for the left command
# (that is supposed to be executed in the left side of the pipe).
reparse_left_arguments() {
	MINUS_MINUS_SIDE=-1
	reparse_arguments "$@"
}

# Prepare arguments for setting them in "eval ..." for the right command
# (that is supposed to be executed in the right side of the pipe).
reparse_right_arguments() {
	MINUS_MINUS_SIDE=+1
	reparse_arguments "$@"
}

# =========================================================================

# EOF