How do I get the IP address into a batch-file variable?

@echo off

FOR /F "tokens=4 delims= " %%i in ('route print ^| find " 0.0.0.0"') do set localIp=%%i

echo Your IP Address is: %localIp%

The following code works on any locale of any platform since Windows XP and it looks for the network IP from a (more or less) random of your network cards. It will never take longer than a few milliseconds.

for /f "delims=[] tokens=2" %%a in ('ping -4 -n 1 %ComputerName% ^| findstr [') do set NetworkIP=%%a
echo Network IP: %NetworkIP%

The following one looks for your public IP instead and works on Windows 7 and newer machines.

for /f %%a in ('powershell Invoke-RestMethod api.ipify.org') do set PublicIP=%%a
echo Public IP: %PublicIP%  

You can find detailed explanations of these commands on my blog.

This will print the IP addresses in the output of ipconfig:

@echo off
set ip_address_string="IPv4 Address"
rem Uncomment the following line when using older versions of Windows without IPv6 support (by removing "rem")
rem set ip_address_string="IP Address"
echo Network Connection Test
for /f "usebackq tokens=2 delims=:" %%f in (`ipconfig ^| findstr /c:%ip_address_string%`) do echo Your IP Address is: %%f

To only print the first IP address, just add goto :eof (or another label to jump to instead of :eof) after the echo, or in a more readable form:

set ip_address_string="IPv4 Address"
rem Uncomment the following line when using older versions of Windows without IPv6 support (by removing "rem")
rem set ip_address_string="IP Address"
for /f "usebackq tokens=2 delims=:" %%f in (`ipconfig ^| findstr /c:%ip_address_string%`) do (
    echo Your IP Address is: %%f
    goto :eof
)

A more configurable way would be to actually parse the output of ipconfig /all a little bit, that way you can even specify the adapter whose IP address you want:

@echo off
setlocal enabledelayedexpansion
::just a sample adapter here:
set "adapter=Ethernet adapter VirtualBox Host-Only Network"
set adapterfound=false
echo Network Connection Test
for /f "usebackq tokens=1-2 delims=:" %%f in (`ipconfig /all`) do (
    set "item=%%f"
    if /i "!item!"=="!adapter!" (
        set adapterfound=true
    ) else if not "!item!"=="!item:IP Address=!" if "!adapterfound!"=="true" (
        echo Your IP Address is: %%g
        set adapterfound=false
    )
)

In Windows 7:

for /f "tokens=1-2 delims=:" %%a in ('ipconfig^|find "IPv4"') do set ip=%%b
set ip=%ip:~1%
echo %ip%
pause