BASH_REMATCH stack: a secret bash feature :O

bashrematch_stack.bash

#!/bin/bash --
# https://lists.gnu.org/archive/html/bug-bash/2022-05/msg00052.html

bashrematch_push () {
    local BASH_REMATCH a
    for a
        do [[ $a =~ .* ]]
    done
}
bashrematch_pop () {
    local i
    for (( i = (${1-1}); i; --i )); do
        printf '%s\n' "$BASH_REMATCH"
        unset -v BASH_REMATCH
    done
}

# Examples:
#   bash-5.1$ printf '%s\n' a b c | bashrematch_tac
#   c
#   b
#   a
#
#   bash-5.1$ printf 'd\ne\nf\ng' | bashrematch_tac
#   gf
#   e
#   d
bashrematch_tac () {
    local REPLY i=0
    while read -r; do
        bashrematch_push "$REPLY"
        (( ++i ))
    done
    printf '%s' "$REPLY"
    bashrematch_pop "$i"
}

# Examples:
#   bash-5.1$ a=( el1 el2 el3 ); bashrematch_reverse "${a[@]}"
#   el3
#   el2
#   el1
bashrematch_reverse () {
    bashrematch_push "$@"
    bashrematch_pop "$#"
}