Boilerplate for new POSIX shell scripts

newscript.sh

#!/bin/sh

prog_name=${0##*/}
version=0.1
version_text="Boilerplate for new scripts v$version";
options="h q v V d " # basic opts
options+="o: " # script specifics
help_text="Usage: $prog_name [-o <text>] [-hqvV] [<file>]...

  ${version_text}

    -o <text>  Set an option with a parameter

    -h         Display this help text and exit
    -q         Quiet
    -v         Verbose mode
    -V         Display version information and exit
"

### Script variable defaults here:
#opt_o=''

main() {
    set_defaults; # nl/cr/tab/esc & traps
    parse_options "$@";
    shift $((OPTIND-1));
    # If we want to use `getopts` again, this has to be set to 1.
    OPTIND=1;

    # shellcheck disable=2154
    {
        $opt_o && info "option 'o' has value '$val_o'";

        $opt_h && usage;
        $opt_V && version;
        $opt_q && info() { :; }
        $opt_d || debug() { :; }
        $opt_v && info "verbose mode is on";
    }

  _i=1;
  for _file do
    info "operand $_i is '$_file'";
    _i=$((_i+1));
  done
  unset _i _file;

  [ -t 0 ] || info "stdin is not a terminal";
}

##########################################################################

# shellcheck disable=2034,2046
set_defaults() {
    set -e;
    trap 'clean_exit' EXIT TERM;
    trap 'clean_exit HUP' HUP;
    trap 'clean_exit INT' INT;
    IFS=' ';
    set -- $(printf '\n \r \t \033');
    nl=$1 cr=$2 tab=$3 esc=$4;
    IFS=\ $tab;
}

# For a given optstring, this function sets the variables
# "opt_<optchar>" to true/false and val_<optchar> to its parameter.
parse_options() {
    for _opt in $options; do
        # The POSIX spec does not say anything about spaces in the
        # optstring, so lets get rid of them.
        _optstring=$_optstring$_opt;
        eval "opt_${_opt%:}=false";
    done

    while getopts ":$_optstring" _opt; do
        case $_opt in
            :) usage "option '$OPTARG' requires a value" ;;
            \?) usage "unrecognized option '$OPTARG'" ;;
            *)
                eval "opt_$_opt=true";
                [ -n "$OPTARG" ] &&
                    eval "val_$_opt=\$OPTARG";
            ;;
        esac
    done
    unset _opt _optstring OPTARG;
}

datestamp() {
    _format=${*:-"%Y-%m-%d %H:%M:%S%z"};
    echo $(date +"$_format");
}

info()    { printf '%b\n' "$*"; }
debug()   { info 'DEBUG: ' "$*" >&2; }
version() { info "$version_text"; exit; }

error() {
    _error=${1:-1};
    shift;
    printf '%s: Error: %s\n' "$prog_name" "$*" >&2;
    exit "$_error";
}

usage() {
    [ $# -ne 0 ] && {
        exec >&2;
        printf '%s: %s\n\n' "$prog_name" "$*";
    }
    printf %s\\n "$help_text";
    exit ${1:+1};
}

clean_exit() {
    _exit_status=$?;
    trap - EXIT;
    info "exiting";

    [ $# -ne 0 ] && {
        trap - "$1";
        kill -s "$1" -$$;
    }
    exit "$_exit_status";
}

main "$@"