Detecting leading spaces in a string using bash

detect_leading_spaces.sh

#! /usr/bin/env bash

# This function will remove all spaces surrounding a string by
# using echo and IFS. Then it aggressively removes instances of
# the string from itself and everything that follows. In other words
# it returns a string that is the difference of itself with spaces
# and without spaces, specifically leading spaces. The length
# of the returned string is equal to the number of leading spaces.

# Not tested for tabs and other characters, but more fine-tuned
# use of IFS should allow for detection of those. It just wasn't
# necessary for my use.

# shellcheck disable=2116,2086,1083,2155,2046
function detect_leading_spaces {
    # this is used by reading the return value using $?
    # immediately after it is executed

    # using a subshell to simplify handling IFS restoration
    return $(
        IFS=$' '
        despaced=$( printf ${1} )
        leading=$( IFS='' && eval printf \"\${1//${despaced}*}\" )
        printf ${#leading}
    )
}

# use like this:
detect_leading_spaces "  test string   " # test string has 2 leading spaces, 1 in the middle and 3 trailing spaces
# assign or use $?
echo $?
# $? must be used immediately after calling the function or the return value
# will be masked