find /etc -maxdepth 1 -type f | wc -l
32

at ETC directory has 32 files.

ATmega32u4 Code:

#include <Process.h>
void setup() {
  Bridge.begin();   // Initialize the Bridge
  Serial.begin(9600);   // Initialize the Serial
  while (!Serial);  // Wait until a Serial Monitor is connected.
  countfiles();
}
void loop() { }
void countfiles() {
  Process p;
  p.runShellCommand("find /etc -maxdepth 1 -type f | wc -l");
  while (p.running());
  while (p.available()) {
    int result = p.parseInt();          // look for an integer
    Serial.println(result);       // print the number as well
    break;
  }
}