vlib: os.execute and arguments with linefeeds causes invalid exit_code about v

[hholst80]

@felipensp good-first-issue To invite newcomers to start working on vlib?

[HydroH]

Hi, I found there was logic on handling such characters, but they were commented out in a previous commit:
1bfcdaa#diff-61ea029cc6cc2d797366920e750069365bfbdddee28865dd540928cbd6048c95R76
What is the reason behind this?

[hholst80]

Spawn ["sh", "-c", arg] with arg untouched.

I think we should strive to allow exactly the same thing as the native "sh -c" will allow. A little experimentation reveals that we should not strip away the line feeds rather keep them. Control flow characters are perfectly valid to send to sh -c arg as arg. A linefeed will be interpreted as a sequence of statements. One can probably send a shell script as-is as the arg just by keeping the control characters as-is.

sh-5.2# sh -c "$(echo -e "ps 1\n\n")"
  PID TTY      STAT   TIME COMMAND
    1 ?        S      0:00 /sbin/init
sh-5.2# sh -c "ps 1"
  PID TTY      STAT   TIME COMMAND
    1 ?        S      0:00 /sbin/init
sh-5.2# sh -c "$(echo -e "ps\n1\n")"
  PID TTY          TIME CMD
25947 pts/4    00:00:01 fish
26060 pts/4    00:00:00 sh
26105 pts/4    00:00:00 sh
26106 pts/4    00:00:00 ps
sh: line 2: 1: command not found
sh-5.2# sh -c "$(echo -e "echo 1\necho 2")"
1
2
sh-5.2# sh -c "$(echo -e "true\nfalse")"
sh-5.2# echo $?
1
sh-5.2# sh -c "$(echo -e "false\ntrue")"
sh-5.2# echo $?
0
sh-5.2#

Notice that sh responded sh: line 2: 1: command not found there. arg is actually a script. everything allowed in a script should be allowed in arg.

[hholst80]

The tl;dr from the above analysis is that we should feed the linefeeds etc as-is. No filtering should be done.

The issue I ran into is due is the redirection stuff we add on the top. I think we can remove that. popen does nothing of that sort and I think we do not want to add a bunch of logic on top of what the C popen/pclose does.

EDIT: I was too late to the party to have an opinion on that, as we already had tests that checked for the stderr redirection. ;-) Anyways, I reworked how redirection is done to be a separate statement up front. This is likely very fragile and will only work for simple "one liners". If raw Posix shell execution is required, use popen.