Fix sudofox#4: Compatibility with ZSH

This commit introduces several fixes to make sure the program works in
bash and zsh
- conditions use the correct [[]] syntax
- the random generator has been replaced with the use of /dev/urandom
- fixed the '/' separated arrays of words to work in both shells
- fixed the way array elements are accessed (0-indexes in bash but
  1-indexed in zsh)

The PROMPT_COMMAND in the readme has been updated to provide a working
example with zsh (@AlonsoCGonzaled suggestion)

@mja00 suggested using the LC_CTYPE=C variable for the random generator
to ensure compatibility with MacOS

README.md

@@ -19,12 +19,18 @@ To use the `mommy` function, you can source the `shell-mommy.sh` script in your
 . /path/to/shell-mommy.sh
 ```
 
-If you'd like it to always show a message after each command, you can define a custom `PROMPT_COMMAND` like so:
+If you'd like it to always show a message after each command, you can define a custom `PROMPT_COMMAND` like so (bash):
 
 ```
 export PROMPT_COMMAND="mommy \\$\\(exit \$?\\); $PROMPT_COMMAND"
 ```
 
+On zsh, you can add the following to your `~/.zshrc`
+
+```bash
+precmd() { mommy "$PROMPT_COMMAND" }
+```
+
 ## Configuration
 
 The `mommy` function has several customizable options that can be set using environment variables:
@@ -78,4 +84,4 @@ mommy ls
 
 # Output:
 # That's a good kiddo~ ❤️
-```
+```

shell-mommy.sh

@@ -84,22 +84,34 @@ mommy() {
   if [[ -n "${SHELL_MOMMYS_NEGATIVE_RESPONSES:-}" ]]; then
     NEGATIVE_RESPONSES=("${SHELL_MOMMYS_NEGATIVE_RESPONSES[@]}")
   fi
-
+
+  # generate a random base 10 number using /dev/urandom
+  random() {
+    rd_number=$(LC_CTYPE=C tr -cd '[:digit:]' < /dev/urandom | head -c 6)
+    # 10# is used to force the number to be considered as base 10, otherwise a number starting
+    # with `08` will fail in bash
+    echo "10#$rd_number"
+  }
+
   # split a string on forward slashes and return a random element
   pick_word() {
-    IFS='/' read -ra words <<<"$1"
-    index=$(($RANDOM % ${#words[@]}))
-    echo "${words[$index]}"
+    if [[ -n "$ZSH_VERSION" ]]; then
+      words=(${(@s:/:)1})
+    else
+      words=(${1//\// })
+    fi
+    index=$(($(random) % ${#words[@]}))
+    echo "${words[@]:$index:1}"
   }
 
   pick_response() { # given a response type, pick an entry from the array
 
-    if [ "$1" == "positive" ]; then
-      index=$(($RANDOM % ${#POSITIVE_RESPONSES[@]}))
-      element=${POSITIVE_RESPONSES[$index]}
-    elif [ "$1" == "negative" ]; then
-      index=$(($RANDOM % ${#NEGATIVE_RESPONSES[@]}))
-      element=${NEGATIVE_RESPONSES[$index]}
+    if [[ "$1" == "positive" ]]; then
+      index=$(($(random) % ${#POSITIVE_RESPONSES[@]}))
+      element=${POSITIVE_RESPONSES[@]:$index:1}
+    elif [[ "$1" == "negative" ]]; then
+      index=$(($(random) % ${#NEGATIVE_RESPONSES[@]}))
+      element=${NEGATIVE_RESPONSES[@]:$index:1}
     else
       echo "Invalid response type: $1"
       exit 1
@@ -128,7 +140,7 @@ mommy() {
   success() {
     (
       # if we're only supposed to show negative responses, return
-      if [ "$DEF_ONLY_NEGATIVE" == "true" ]; then
+      if [[ "$DEF_ONLY_NEGATIVE" == "true" ]]; then
         return 0
       fi
       # pick_response for the response type