#!/bin/ksh
# Usage: findstr [string]
# Read lines from standard input and for each line read:
# 1. Print the input line.
# 2. Print the offset of each occurrence of string ("ab" if no operands are
#    given) in that line (with the 1st character on each line being offset 1.
# 3. Print the number of occurrences of string found on the input line.
# Note that if the string operand contains any non-alphnumeric characters, the
# results are unspecified.
string=${1:-ab}
while IFS= read -r line
do	printf 'Input: "%s"\n' "$line"
	cnt=0
	offset=1
	while [ "${line#*$string}" != "$line" ]
	do	cnt=$((cnt + 1))
		left=${line#*$string}
		offset=$((offset + ${#line} - ${#left} - ${#string}))
		printf '\t"%s" found at offset %d\n' "$string" $offset
		offset=$((offset + ${#string}))
		line=$left
	done
	printf '\t"%s" found %d time(s).\n' "$string" $cnt
done

printf '%s\n' abcabc abcdedabxxxxabxxxab xxxxxx | ./findstr

Input: "abcabc"
	"ab" found at offset 1
	"ab" found at offset 4
	"ab" found 2 time(s).
Input: "abcdedabxxxxabxxxab"
	"ab" found at offset 1
	"ab" found at offset 7
	"ab" found at offset 13
	"ab" found at offset 18
	"ab" found 4 time(s).
Input: "xxxxxx"
	"ab" found 0 time(s).

printf '%s\n' abcabc abcdedabxxxxabxxxab xxxxxx|./findstr xx

Input: "abcabc"
	"xx" found 0 time(s).
Input: "abcdedabxxxxabxxxab"
	"xx" found at offset 9
	"xx" found at offset 11
	"xx" found at offset 15
	"xx" found 3 time(s).
Input: "xxxxxx"
	"xx" found at offset 1
	"xx" found at offset 3
	"xx" found at offset 5
	"xx" found 3 time(s).