/usr/bin/env -0 for non-Linux systems

Question

Consider I want to programmatically read the environment of an interactive shell. Now, starting a shell, running /usr/bin/env and capturing its output seems like a good solution. But only up until the moment we realize that variable values can have line breaks:

$ export LINE0='VALUE0
> LINE1=VALUE1'
$ env | grep ^LINE
LINE0=VALUE0
LINE1=VALUE1

So capturing the output of env -0 (NULL-separated entries) seems like a better approach, but this only applies to GNU env, so is mostly Linux-specific.

Is there any portable (POSIX or BSD) way to get the NULL-separated list of environment variables, using only the standard command line tools (may use awk, but no perl/python/ruby allowed)?

Answer 1

I wonder how you plan to restore that captured environment, since no shell but zsh supports nul bytes in its variables.

Anyways, you could use awk to escape \ as \\ and the newline as \n, and still use a newline to separate the name=val entries:

awk 'BEGIN{
  for(e in ENVIRON){
    v = e "=" ENVIRON[e];
    gsub(/\\/, "&&", v); gsub(/\n/,"\\n",v); print v
  }
}'

fzd$ env - $'foo\\bar\nquux=foo\\bar\nquux' lol=cat printenv
lol=cat
foo\bar
quux=foo\bar
quux

fzd$ env - $'foo\\bar\nquux=foo\\bar\nquux' lol=cat awk 'BEGIN{
  for(e in ENVIRON){
    v = e "=" ENVIRON[e];
    gsub(/\\/, "&&", v); gsub(/\n/,"\\n",v); print v
  }
}'
foo\\bar\nquux=foo\\bar\nquux
lol=cat