Install and auto-update cygwin from command line.

cygwin.bat

@echo off
cls

:: CONSTANTS
:: Path cygwin should get installed to.
set cygwin_dir=C:\Cygwin
set cygwin_url=https://cygwin.com/setup-x86_64.exe

:: The script calls itself after copying to the installation directory with the parameter
:: --origin set to the originating file. So it can delete the obsolete copy it originated from.
if not [%1] == [] (
    if ["%1"] == ["--origin"] (
        if exist "%~2" (
            echo $ del "%~2"
            del "%~2"
        ) else (
            echo Origin file '%~2' not found!
            goto :eof
        )
    ) else (
        echo Wrong command line args!
        goto :eof
    )
)

echo cygwin_url = %cygwin_url%
echo cygwin_dir = %cygwin_dir%

for %%i in ("%cygwin_url%") do ( set setup_file=%%~nxi )
echo setup_file = %setup_file%

set setup_path=%cygwin_dir%\%setup_file%
echo setup_path = %setup_path%

:: create setup dir if necessary
if not exist %cygwin_dir% mkdir %cygwin_dir%

:: copy itself and execute again. ATTENTION: %~dp0 contains trailing '\'
if not [%cygwin_dir%\] == [%~dp0] (
    echo $ copy "%~f0" "%cygwin_dir%" /y
    copy "%~f0" "%cygwin_dir%" /y
    echo $ "%cygwin_dir%\%~nx0" --origin "%~f0"
    "%cygwin_dir%\%~nx0" --origin "%~f0"
    goto :eof
)

echo $ pushd %cygwin_dir%
pushd %cygwin_dir%

echo $ curl "%cygwin_url%" -o"%setup_file%"
curl "%cygwin_url%" -o"%setup_file%"

echo $ %setup_path% -a x86_64 -D -f -l "%cygwin_dir%" -d -n -O -s http://cygwin.mirror.constant.com/ -R "%cygwin_dir%" -g -v -W
%setup_path% -a x86_64 -f -l "%cygwin_dir%" -d -n -O -s http://cygwin.mirror.constant.com/ -R "%cygwin_dir%" -g -v -W

echo $ popd
popd

:: REFERENCES
:: https://ss64.com/nt/syntax-args.html
:: https://cygwin.com/faq/faq.html#faq.setup.cli