gave sheelutils a more appropriate name and added which

external_control/external_control.ino

@@ -248,7 +248,7 @@ void getAndRunCommand(){
       "    lock the Arduino's state by running an infinite loop\n\r"
       "  L loop\n\r"
       "    usage: followed by a 5 digit uint16_t number,\n\r"
-      "      then one of the lowercas commands with arguments\n\r"
+      "      then one of the lowercase commands with arguments\n\r"
       "    repeat the command given as an argument\n\r"
       "  m set mode\n\r"
       "    usage: followed by two digit pin number and o or i\n\r"
@@ -273,7 +273,8 @@ void getAndRunCommand(){
       "    sets pullup resistor for input pins\n\r"
       "    \"digitalWrite\"\n\r"
       "  p write pwm\n\r"
-      "    usage: followed by two digit pin number and three digit value between 000 and 255\n\r"
+      "    usage: followed by two digit pin number and three digit value\n\r"
+      "      between 000 and 255\n\r"
       "    \"analogWrite\"\n\r"
       "  t toggle pin state\n\r"
       "    usage: followed by two digit pin number\n\r"

shellutils/which

@@ -0,0 +1,57 @@
+#!/bin/sh
+internal_path="$(echo $PATH | sed -e 's/:/\n/g')"
+
+while true; do
+    if getopts "ac:h" arg; then
+        true # do nothing
+    else
+        break
+    fi
+    case $arg in
+        a)
+            all="yes"
+            shift
+            ;;
+        c)
+            internal_path="$(echo $OPTARG | sed -e 's/:/\n/g')"
+            shift 2
+            ;;
+        h)
+            echo "Usage: $0 [-a] [-c <custom path>] <command>"
+            echo \
+'Options:
+ -a return all results if multiple found
+ -c <custom path> search in the specified path instead of $PATH
+ -h display this message'
+            echo \
+"Exit codes:
+ 0 found
+ 1 not found
+ 2 error"
+            exit 0
+            ;;
+        ?)
+            echo "Usage: $0 [-a] [-c <custom path>] <command>"
+            exit 2
+            ;;
+    esac
+done
+
+IFS='
+'
+for directory in $internal_path; do
+    if [ -e "$directory/$1" ]; then
+        echo "$directory/$1"
+        if [ "$all" = "yes" ]; then
+            found="yes"
+        else
+            exit 0
+        fi
+    fi
+done
+
+if [ "$found" = "yes" ]; then
+    exit 0
+else
+    exit 1
+fi