bash in-process string substitution with one capturing group

bash_sub.sh

# Bash parameter expansion syntax for ${parameter/match/replacement}:
# https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html
#
# Bash pattern matching syntax:
# https://www.gnu.org/software/bash/manual/html_node/Pattern-Matching.html
#
# Bash conditional [[ string =~ pattern ]] and $BASH_REMATCH syntax:
# https://www.gnu.org/software/bash/manual/html_node/Conditional-Constructs.html
#
# Recipe to do a string replace with capturing:
# https://stackoverflow.com/a/22261643

# String substitution with limited support for regex and capturing match
sub() {
    local string="$1"
    local pattern="$2"
    local replacement="$3"
    # If no match, output original string and return false
    [[ $string =~ $pattern ]] || { echo "$string" && return 1; }
    # Save the first captured string match, if any
    local match=${BASH_REMATCH[1]}
    # Expand replacement token $1 with captured string
    replacement=${replacement/\$1/$match}
    # Change regex start anchor to parameter expansion start anchor
    pattern=${pattern/#^/#}
    # Update pattern to replace capturing match with literal matched value
    pattern=${pattern/\(*\)/$match}
    # Replace the entire literal matched pattern with expanded replacement
    echo ${string/$pattern/$replacement}
}