Introduction of env --null

Question

I have tried to extract environment variables in a Python process with help of env --null, which works even for environment variables containing newline character.

But on some machines I have received an error:

> env -0
env: invalid option -- '0'

> env --null
env: unrecognized option '--null'

> env --version
env (GNU coreutils) 6.12
Copyright (C) 2008 Free Software Foundation, Inc.

In which version was the argument introduced? Is there any alternative command to extract the environment?

On Linux: `cat /proc/self/environ` – Stéphane Chazelas Jan 13 '15 at 16:56 — Stéphane Chazelas, Jan 13 '15 at 16:56

cuonglm · Accepted Answer · 2015-01-13T17:34:00.497

6

Option -0/--null was first introduce on 28-10-2009, and release with GNU coreutils version 8.1.

If your coreutils is too old, you should upgrade. Or you can use perl:

perl -e '$ENV{_}="/usr/bin/env"; print "$_ => $ENV{$_}\0" for keys %ENV'

As @Stéphane Chazelas pointed out in his comment, the above approach doesn't include environment strings that don't contain =, duplicated environment variables or environment variables with null name.

If you are in Linux, you can use (Thanks @Stéphane Chazelas again):

cat /proc/self/environ

edited Jan 13 '15 at 17:34

answered Jan 13 '15 at 16:33

cuonglm

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Note that it doesn't include the environment strings that don't contain `=` or duplicated env vars or env vars with the null name (`=value` env strings). – Stéphane Chazelas Jan 13 '15 at 17:03
@StéphaneChazelas: Can you give example for each of them? I even don't know how can we create env vars with null name. – cuonglm Jan 13 '15 at 17:12
`tcc -run - <<< 'int main() { char*e[] = { "a=b", "a=c", "", "=", 0}; execle("/usr/bin/env", "env", "-0", 0, e); }'` – Stéphane Chazelas Jan 13 '15 at 17:19
@StéphaneChazelas: Thanks for that information, updated my answer. – cuonglm Jan 13 '15 at 17:34

score 3 · Answer 2 · answered Jan 13 '15 at 16:14

If you are working with python anyway you could use:

import os
import sys

for k in sorted(os.environ):
    if k == '_':
        v = '/usr/bin/env'
    else:
        v = os.environ[k]
    sys.stdout.write("{}={}\0".format(k, v))

to get very similar output compared to env --null.

Introduction of env --null

2 Answers2