CCS/TM4C123GH6PM: UART Communication between computer and TIVA C

Tool/software: Code Composer Studio

Hii, 

I'am manu and i'm trying UART interfacing with tiva c board. I referred number of tutorials but i cannot understand. Basically there is lot more tutorials available to send a character and to echo it in the terminal. I worked in arduino board before. its feature like, if i type a string and i need to put enter then only the data pass to the further operation in serial monitor but here it is something strange for me. how can i achieve same thing in TIVA C. 

I would like to interface SIM800l and TIVA C, to do so i should send AT commands. In below example only characters are sending and receiving. How do i know the transmission ends ? For example if i sen AT to GSM module it should response OK. how do i do that ? Please help me i'm trying this from last week 

#include "inc/hw_memmap.h"
#include "inc/hw_types.h"
#include "driverlib/gpio.h"
#include "driverlib/pin_map.h"
#include "driverlib/sysctl.h"
#include "driverlib/uart.h"


int main(void) {
SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN | SYSCTL_XTAL_16MHZ);
SysCtlPeripheralEnable(SYSCTL_PERIPH_UART0);
SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);
GPIOPinConfigure(GPIO_PA0_U0RX);
GPIOPinConfigure(GPIO_PA1_U0TX);
GPIOPinTypeUART(GPIO_PORTA_BASE, GPIO_PIN_0 | GPIO_PIN_1);
UARTConfigSetExpClk(UART0_BASE, SysCtlClockGet(), 115200,
(UART_CONFIG_WLEN_8 | UART_CONFIG_STOP_ONE | UART_CONFIG_PAR_NONE));
UARTCharPut(UART0_BASE, 'E');
UARTCharPut(UART0_BASE, 'n');
UARTCharPut(UART0_BASE, 't');
UARTCharPut(UART0_BASE, 'e');
UARTCharPut(UART0_BASE, 'r');
UARTCharPut(UART0_BASE, ' ');
UARTCharPut(UART0_BASE, 'T');
UARTCharPut(UART0_BASE, 'e');
UARTCharPut(UART0_BASE, 'x');
UARTCharPut(UART0_BASE, 't');
UARTCharPut(UART0_BASE, ':');
UARTCharPut(UART0_BASE, ' ');
while (1)
{
if (UARTCharsAvail(UART0_BASE)) UARTCharPut(UART0_BASE, UARTCharGet(UART0_BASE));
}
}