Implement printenv

[ShenTengTu]

Prepare for printenv implementation.

Currently, I implement a simple function of printing available parameters, which can be used as a template reference for developing other utilities in the future.

[ShenTengTu]

The feature (environment variable printing) is basically completed.

The order of os.environ() is different from the original printenv(run on Ubuntu 18.04, coreutils 8.28).

See comment-875244187.

[ShenTengTu]

I am writting a testing script, I get different output from os.execute.

In terminal, printenv --null LANGUAGE LANG output like following (run on Ubuntu 18.04, coreutils 8.28):

zh_TW:zhzh_TW.UTF-8

Use os.execute to execute the command (run on V 0.2.2 6dde9f7):

result_origin := os.execute('printenv --null LANGUAGE LANG')
println(result_origin.output)

the output is not zh_TW:zhzh_TW.UTF-8, but zh_TW:zh

[JalonSolov]

Since it is important that the output is as correct as possible (even if it's in a different order), I'd prefer to hold this until the the V issue is fixed. Any objections?

[ShenTengTu]

Since it is important that the output is as correct as possible (even if it's in a different order), I'd prefer to hold this until the the V issue is fixed. Any objections?

I will commit the initial version of the test script and add comments about the issues to the code, then wait for the issues to be resolved.

[ShenTengTu]

The order of os.environ() is different from the original printenv(run on Ubuntu 18.04, coreutils 8.28).

original printenv output is like:

CLUTTER_IM_MODULE=...
FNM_LOGLEVEL=...
LS_COLORS=...
DENO_INSTALL=...
FNM_ARCH=...
...

In current V implementation, I use os.environ() to fetch all env :

for k, v in os.environ() {
	mut s := '$k=$v'
	if nul_terminate {
		print(s)
	} else {
		println(s)
	}
}

The output is like:

PYENV_VIRTUALENV_INIT=...
LESSOPEN=...
USER=...
MPY_PATH=...
LANGUAGE=...
...

The original output has a specific order, not just in alphabetical order.

• original printenv source code: printenv.c#L115
• os.environ()source code in V: environment.c.v#L75

[spytheman]

The problem occurs if you do v run file.v, because in this case V itself manipulates the environment (it sets VEXE and VTMP for example).

If you instead first compile your program, and then run it, it will produce the same as printenv: