expr.sh

expr extend .. notation

#! /bin/sh
# (c) 2025/05/26 yoya@awm.jp
# Usage: expr.sh 1 + .. 20  # => 210 
# Usage: expr.sh 1 \* .. 5  # => 120

output=()
mode=0
for a in "$@"
do
    if [ "$a" == ".." ]; then
	n=`expr "${#output[@]}"`
	left=${output[`expr $n - 2`]}
	op=${output[`expr $n - 1`]}
        mode=1  # loop mode
        continue
    fi
    if [ $mode -eq 0 ]; then
        output+=("$a")
    elif [ $mode -eq 1 ]; then
	left_next=`expr $left + 1`
	right=$a
	for i in `seq $left_next $right`; do
	    if [ $i -gt $left_next ]; then
		output+=("$op")
	    fi
            output+=("$i")
        done
        mode=0
    fi
    prev=$a
done

command="expr"
for a in "${output[@]}"
do
    command="$command '$a'"
done
eval $command