That's easy:

Code:

FILE=${1?You must have a filename}
STR=${2?You need string to index}

_index() #@ Store position of $2 in $1 in $_INDEX
{
    case $1 in
        "")  _INDEX=0; return 1 ;;
        *"$2"*) ## extract up to beginning of the matching portion
              idx=${1%%"$2"*}
              ## the starting position is one more than the length
              _INDEX=$(( ${#idx} + 1 )) ;;
        *) _INDEX=0; return 1 ;;
    esac
}

file=$( cat "$FILE" )

_index "$file" "$STR"

printf 'The position of "%s" is %d\n' "$STR" "$_INDEX"

Why sed? It is not much use as a programming language; awk can do much more and in a more legible manner.

What's a "tab space"? Do you mean a tab?

Use a space. Put verbatim text inside [code] tags so that a monospace font is used in a <PRE> element.

That's:

Code:

    BAA BAA
   ABC 222 555
    XYZ  123
    BAA BAA

Or is it?

What did you do to get that result? Describe the process.

Do the same for your other results.