esp8266/libraries/ESP8266WebServer/examples/PathArgServer/PathArgServer.ino

#include <ESP8266WiFi.h>
#include <WiFiClient.h>
#include <ESP8266WebServer.h>
#include <ESP8266mDNS.h>

#include <uri/UriBraces.h>
#include <uri/UriRegex.h>

#ifndef STASSID
#define STASSID "your-ssid"
#define STAPSK "your-password"
#endif

const char *ssid = STASSID;
const char *password = STAPSK;

ESP8266WebServer server(80);

void setup(void) {
  Serial.begin(115200);
  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);
  Serial.println("");

  // Wait for connection
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");
  Serial.print("Connected to ");
  Serial.println(ssid);
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());

  if (MDNS.begin("esp8266")) { Serial.println("MDNS responder started"); }

  server.on(F("/"), []() {
    server.send(200, "text/plain", "hello from esp8266!");
  });

  server.on(UriBraces("/users/{}"), []() {
    String user = server.pathArg(0);
    server.send(200, "text/plain", "User: '" + user + "'");
  });

  server.on(UriRegex("^\\/users\\/([0-9]+)\\/devices\\/([0-9]+)$"), []() {
    String user = server.pathArg(0);
    String device = server.pathArg(1);
    server.send(200, "text/plain", "User: '" + user + "' and Device: '" + device + "'");
  });

  server.begin();
  Serial.println("HTTP server started");
}

void loop(void) {
  server.handleClient();
}