How to split the output of a `printenv` shell command?

Question

Basically, I want to split a multiline string at the regular expression that, in Perl, would be specified with \n(?=[^\W\d]\w*=).

Note that the Perl regexp features a "zero-width lookahead match" ((?=...)), meaning that the substrings that match this part of the regexp will not be "consumed"; they will appear in their corresponding entries in the resulting list.

For example, the string whose printed representation is

A=1
B_C_D=
foo
bar
baz
  =whatever=
X_Y_Z=quux

would be split into the following three-element list:

("A=1" "B_C_D=\nfoo\nbar\nbaz\n  =whatever=" "X_Y_Z=quux\n")

Even though Elisp regexps do not support lookahead/lookbehind expressions, this sort of splitting problem (in which part or all of each matching substring is not consumed) is common enough that I hope there are some other standard ways to solve it in Elisp.

Moreover, the ultimate goal here is to split the output of the shell command

/usr/bin/zsh -ilc 'printenv' 2>/dev/null

so that each element of the result would correspond to one "setting" of an environment variable¹. So I also figure that Elisp may possibly have functions that facilitate the handling of this special case².

---

^{1 The desired result is conceptually similar to value of the variable process-environment, but in general it is not be identical to it. Also, the side-effects associated with setting and updating process-environment do not enter into my problem.}

^{2 Unfortunately, it appears that process-environment is initialized in C-code, so whatever functions do that are not available in Elisp.}

Answer 1

This might not be quite the answer you want, but use printenv -0 instead. This puts a NUL between each "line" of output, which in this case will be between each var=value pair:

TMUX_PANE=%0^@test=foo
bar
baz
^@SHLVL=2

Parsing that will be much easier.

Code:

(split-string (shell-command-to-string "printenv -0") "\0" t) 

Answer 2

I think db48x has the right answer for your underlying problem (without the -0 argument, printenv's output is ambiguous in case one of your env vars contains ...\nfoo=bar).

But as for how to do it in Elisp, I'd do it as follows:

(defun parse-foo (str)
  (with-temp-buffer
    (insert str)
    (goto-char (point-min))
    (let ((start (point))
          (strs ()))
    (while (re-search-forward "\n\\w+=" nil 'move)
      (push (buffer-substring start (match-beginning 0)) strs)
      (setq start (1+ (match-beginning 0))))
    (cons (buffer-substring start (point)) strs)))