feat: Implement MODULAR flavor

Fixes #4.

Signed-off-by: 林博仁(Buo-ren, Lin) <Buo.Ren.Lin@gmail.com>

Author: brlin-tw

README.md

@@ -28,6 +28,13 @@ Inherited from the [BARE-MINIMUM](#bare-minimum) flavor, but with the following
     + `script_filename`: The full filename of the shell script
     + `script_name`: The name of the shellscript, excluding the filename suffixes
 
+## [MODULAR](modular.sh)
+
+Inherited from the [BASIC](#basic) flavor, but with the following additions:
+
+* The introduction of the `init` function, which enables the moving of the program's main logic to the start of the script file, increases readability.
+* A new `trap_err` function has being implemented to handle the ERR trap so one can immediately recognize that an error has occurred when the `errexit` interpreter behavior is triggered.
+
 ## References
 
 * [The Common / The Common GNU Bash Shell Script Templates · GitLab](https://gitlab.com/the-common/bash-script-templates)  

modular.sh

@@ -0,0 +1,91 @@
+#!/usr/bin/env bash
+# _script_description_
+#
+# Copyright _copyright_effective_year_ _copyright_holder_name_ <_copyright_holder_contact_>
+# SPDX-License-Identifier: CC-BY-SA-4.0
+
+init(){
+    printf \
+        'Info: Operation completed without errors.\n'
+}
+
+printf \
+    'Info: Configuring the defensive interpreter behaviors...\n'
+set_opts=(
+    # Terminate script execution when an unhandled error occurs
+    -o errexit
+    -o errtrace
+
+    # Terminate script execution when an unset parameter variable is
+    # referenced
+    -o nounset
+)
+if ! set "${set_opts[@]}"; then
+    printf \
+        'Error: Unable to configure the defensive interpreter behaviors.\n' \
+        1>&2
+    exit 1
+fi
+
+printf \
+    'Info: Checking the existence of the required commands...\n'
+required_commands=(
+    realpath
+)
+flag_required_command_check_failed=false
+for command in "${required_commands[@]}"; do
+    if ! command -v "${command}" >/dev/null; then
+        flag_required_command_check_failed=true
+        printf \
+            'Error: This program requires the "%s" command to be available in your command search PATHs.\n' \
+            "${command}" \
+            1>&2
+    fi
+done
+if test "${flag_required_command_check_failed}" == true; then
+    printf \
+        'Error: Required command check failed, please check your installation.\n' \
+        1>&2
+    exit 1
+fi
+
+if test -v BASH_SOURCE; then
+    printf \
+        'Info: Configuring the convenience variables...\n'
+    # Convenience variables
+    # shellcheck disable=SC2034
+    {
+        printf \
+            'Info: Determining the absolute path of the program...\n'
+        if ! script="$(
+            realpath \
+                --strip \
+                "${BASH_SOURCE[0]}"
+            )"; then
+            printf \
+                'Error: Unable to determine the absolute path of the program.\n' \
+                1>&2
+            exit 1
+        fi
+        script_dir="${script%/*}"
+        script_filename="${script##*/}"
+        script_name="${script_filename%%.*}"
+    }
+fi
+
+trap_err(){
+    printf \
+        'Error: The program has encountered an unhandled error and is prematurely aborted.\n' \
+        1>&2
+}
+
+printf \
+    'Info: Setting the ERR trap...\n'
+if ! trap trap_err ERR; then
+    printf \
+        'Error: Unable to set the ERR trap.\n' \
+        1>&2
+    exit 1
+fi
+
+init