#include <sourcemod>

#define FILE "addons/test.txt"

public OnPluginStart()
{
       new Handle:file = OpenFile(FILE, "r");

       if (file == INVALID_HANDLE)  
       {  
             SetFailState("Не удалось открыть файл '%s'", FILE);
       }
       else
       {
             new CountLine = 0;

             while (!IsEndOfFile(file))
             {
                   CountLine++;
             }

             PrintToServer("File: %s || Count line: %d", FILE, CountLine);

             CloseHandle(file);
       }
}