Simplify setting multiple environment variables using templates

gittemplater.sh

#!/bin/bash
script_version="1.08"

SUBST="@repo@"
SAVE_IFS="$IFS"

if [[ -z $1  || $1 = "--help" ]]; then
    echo >&2 "Git-specialized version of tool: $script_version"
    echo >&2 "Usage: T_template1=substitution1 ... T_templateN=substitutionN ./envtemplater.sh repo1@template ... repoN@template -- command [arguments]"
    echo >&2 "Example: T_github=ALTURL_${SUBST}=https://github.com/vi/${SUBST}.git ./envtemplater.sh dive@github fdlinecombine@github -- ./submodule_update_alturl.sh --force"
    exit 1
fi

set -e
#set -x

# mangle_submodule_name: 'repo/1/name' -> 'repo_1_name'"
mangle_submodule_name() {
    echo $1 | sed 's/\//_/g'
}

# export mangle_submodule_name for child process:
export -f mangle_submodule_name

while [ "$1" != '--' ]; do
    if [[ $# == 0 ]]; then
        echo >&2 "-- not found in command line"
        exit 4;
    fi

    IFS="@"
    Q=($1)
    IFS=$SAVE_IFS

    reponame=$(mangle_submodule_name "${Q[0]}")
    servicename=${Q[1]}

    TEMPLATE="T_${servicename}"
    TEMPLATE_CONTENT=$(eval "echo \"\$$TEMPLATE\"")

    #echo "reponame = $reponame"
    #echo "servicename = $servicename"
    #echo "TEMPLATE = $TEMPLATE"
    #echo "TEMPLATE_CONTENT = $TEMPLATE_CONTENT"

    if [ -z $TEMPLATE_CONTENT ]; then
        echo >&2 "Template environment variable $TEMPLATE was not found. Please read envtemplater.sh help again and prepare environment correctly!"
        exit 2
    fi

    VALUE="${TEMPLATE_CONTENT//${SUBST}/${reponame}}"
    #echo "VALUE = $VALUE"

    eval "export $VALUE"
    shift
done
shift

exec "$@"