List:
USER=web_user
LOGNAME=web_user
PATH=/
PWD=/
HOME=/home/web_user
LANG=C.UTF-8
_={{{ THIS_PROGRAM }}}

getenv(PATH): /
getenv(NONEXISTENT): (null)
setenv/0(PATH) ret: 0
getenv(PATH) after setenv/0: /
setenv/1(PATH) ret: 0
getenv(PATH) after setenv/1: test2
setenv(SET_VALUE) ret: 0
setenv(SET_VALUE2) ret: 0
getenv(SET_VALUE): test3
getenv(SET_VALUE2): test4
putenv(PUT_VALUE) ret: 0
getenv(PUT_VALUE): test5
getenv(PUT_VALUE) after alteration: Qest5
unsetenv(PUT_VALUE) ret: 0
getenv(PUT_VALUE) after unsetenv: (null)
setenv(0) ret: -1
setenv('') ret: -1
setenv(X=Y) ret: -1
unsetenv('') ret: -1
unsetenv(X=Y) ret: -1
