From e83a66b0bf6c07b03a55dd02d33f701549601db3 Mon Sep 17 00:00:00 2001
From: Gabriel Staples <ercaguy@gmail.com>
Date: Sun, 6 Mar 2022 21:24:05 -0700
Subject: [PATCH] Add useful_scripts/random.sh as a random number generator

---
 useful_scripts/random.sh | 137 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 137 insertions(+)
 create mode 100755 useful_scripts/random.sh

diff --git a/useful_scripts/random.sh b/useful_scripts/random.sh
new file mode 100755
index 0000000..da3559a
--- /dev/null
+++ b/useful_scripts/random.sh
@@ -0,0 +1,137 @@
+#!/usr/bin/env bash
+
+# This file is part of eRCaGuy_dotfiles: https://github.com/ElectricRCAircraftGuy/eRCaGuy_dotfiles
+
+# GS
+# Mar. 2022
+
+# DESCRIPTION:
+#
+# Random number generator for bash. You can specify a range, and it will output a random number
+# in that range--even a negative number if desired.
+
+# INSTALLATION INSTRUCTIONS:
+# 1. Create a symlink in ~/bin to this script so you can run it from anywhere.
+#           cd /path/to/here
+#           mkdir -p ~/bin
+#           ln -si "${PWD}/random.sh" ~/bin/random     # required
+#           ln -si "${PWD}/random.sh" ~/bin/gs_random  # optional; replace "gs" with your initials
+# 2. Now you can use this command directly anywhere you like like in any of these ways:
+#   1. `random`
+#   2. `gs_random`
+
+# REFERENCES:
+# 1. [my own answer with this code]: https://stackoverflow.com/a/71388666/4561887
+# 1. `man bash`, then search for "RANDOM"
+# 1. How to generate random number in Bash?: https://stackoverflow.com/a/1195035/4561887
+
+
+RETURN_CODE_SUCCESS=0
+RETURN_CODE_ERROR=1
+
+HELP_STR="\
+Generate a random integer number according to the usage styles below.
+
+USAGE STYLES:
+    'random'
+        Generate a random number from 0 to 32767, inclusive (same as bash variable 'RANDOM').
+    'random <max>'
+        Generate a random number from 0 to 'max', inclusive.
+    'random <min> <max>'
+        Generate a random number from 'min' to 'max', inclusive. Both 'min' and 'max' can be
+        positive OR negative numbers, and the generated random number can be negative too, so
+        long as the range (max - min + 1) is less than or equal to 32767. Max must be >= min.
+
+This file is part of eRCaGuy_dotfiles: https://github.com/ElectricRCAircraftGuy/eRCaGuy_dotfiles
+See: https://github.com/ElectricRCAircraftGuy/eRCaGuy_dotfiles/blob/master/useful_scripts/random.sh
+"
+
+print_help() {
+    echo "$HELP_STR" | less -RFX
+}
+
+# Get a random number according to the usage styles above.
+# See also `utils_rand()` in utilities.c:
+# https://github.com/ElectricRCAircraftGuy/eRCaGuy_hello_world/blob/master/c/utilities.c#L176
+random() {
+    # PARSE ARGUMENTS
+
+    # help menu
+    if [ "$1" = "-h" ] || [ "$1" = "--help" ]; then
+        print_help
+        exit $RETURN_CODE_SUCCESS
+    fi
+
+    # 'random'
+    if [ $# -eq 0 ]; then
+        min=0
+        max="none"
+    # 'random max'
+    elif [ $# -eq 1 ]; then
+        min=0
+        max="$1"
+    # 'random min max'
+    elif [ $# -eq 2 ]; then
+        min="$1"
+        max="$2"
+    else
+        echo "ERROR: too many arguments."
+        exit "$RETURN_CODE_ERROR"
+    fi
+
+    # CHECK FOR ERRORS
+
+    if [ "$max" = "none" ]; then
+        rand="$RANDOM"
+        echo "$rand"
+        exit "$RETURN_CODE_SUCCESS"
+    fi
+
+    if [ "$max" -lt "$min" ]; then
+        echo "ERROR: max ($max) < min ($min). Max must be >= min."
+        exit "$RETURN_CODE_ERROR"
+    fi
+
+    # CALCULATE THE RANDOM NUMBER
+
+    # See `man bash` and search for `RANDOM`. This is a limitation of that value.
+    RAND_MAX=32767
+
+    range=$((max - min + 1))
+    if [ "$range" -gt "$RAND_MAX" ]; then
+        echo "ERROR: the range (max - min + 1) is too large. Max allowed = $RAND_MAX, but actual" \
+             "range = ($max - $min + 1) = $range."
+        exit "$RETURN_CODE_ERROR"
+    fi
+
+    # NB: `RANDOM` is a bash built-in variable. See `man bash`, and also here:
+    # https://stackoverflow.com/a/1195035/4561887
+    rand=$((min + (RANDOM % range)))
+    echo "$rand"
+}
+
+# Set the global variable `run` to "true" if the script is being **executed** (not sourced) and
+# `main` should run, and set `run` to "false" otherwise. One might source this script but intend
+# NOT to run it if they wanted to import functions from the script.
+# See:
+# 1. *****https://github.com/ElectricRCAircraftGuy/eRCaGuy_hello_world/blob/master/bash/argument_parsing__3_advanced__gen_prog_template.sh
+# 1. my answer: https://stackoverflow.com/a/70662049/4561887
+# 1. https://github.com/ElectricRCAircraftGuy/eRCaGuy_hello_world/blob/master/bash/check_if_sourced_or_executed.sh
+run_check() {
+    # This is akin to `if __name__ == "__main__":` in Python.
+    if [ "${FUNCNAME[-1]}" == "main" ]; then
+        # This script is being EXECUTED, not sourced
+        run="true"
+    fi
+}
+
+# ----------------------------------------------------------------------------------------------------------------------
+# Main program entry point
+# ----------------------------------------------------------------------------------------------------------------------
+
+# Only run main function if this file is being executed, NOT sourced.
+run="false"
+run_check
+if [ "$run" == "true" ]; then
+    random "$@"
+fi