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RE (tilly) 1: Get default login environment

by tilly (Archbishop)
on Sep 22, 2000 at 18:22 UTC ( #33634=note: print w/replies, xml ) Need Help??

in reply to Get default login environment

After looking at exec's documentation I noticed a more general way to do this. You call sh, lying to it about its name. Here is a slightly more general function, does the same thing as above but does not assume you are running bash as your default shell:
sub get_login_env { local %ENV; my $shell = shift || (getpwuid($<))[8]; my $env = `echo env | perl -e 'exec {"$shell"} -sh'`; if (wantarray) { $env =~ s/\\(.)/$1/gs; return map {split /=/, $_, 2} map {split /\n/, $_} $env; } else { return $env; } }
And since someone asked, the reason for localizing %ENV was to clear the environment before calling the login shell. I may trust the login environment to have a sane environment, but I won't trust my current environment to be clean! :-)

This should work on virtually any *nix with virtually any valid shell, and you can choose the shell to be an argument or take the current shell you use (your choice).

Update: (Much later.) Hue-Bond pointed out that the missing | in the grandchild is missing here as well. Fixed.

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RE: RE (tilly) 1: Get default login environment
by merlyn (Sage) on Sep 22, 2000 at 21:01 UTC
      Actually...try this on for size:
      sub get_login_env { local %ENV; my $shell = shift || (getpwuid($<))[8]; my $env = `echo env | perl -e 'exec {"$shell"} -sh'`; if (wantarray) { my @pieces = ($env =~ m/^(.*?)=((?:[^\n\\]|\\.|\\\n)*)/gm); s/\\(.)/$1/g foreach @pieces; return @pieces; } else { return $env; } }
      Doesn't that take care of everything about how the env function encodes the environment? I tried putting = and returns into the name of environment variables and it wouldn't go...

      I edited the RE slightly. I also should note that compared to the effort of launching a Perl process that execs itself into a login shell, a few invocations of the RE engine are unlikely to do much further damage...

      UPDATE (Much later), Corion caught a silly missing | in the line that gets the environment. :-(

      UPDATE 2 (Years later), as the discussion below points out, there was a silly syntax error. Fixed. Believe it or not, I used a version of this snippet for years, but that copy had been typed separately...

        I downloaded this code but it doesn't work! When I try and use it the following error occurs -
        syntax error at line 8, near "m/^(.*?)=((?:[^\n\\]|\\.| +\\\n)*)/gm ;"
        The code to call this sub is also in a format that, novice that I am, I've not seen before -
        %ENV = (%ENV, get_bash_login_env());
        The ENV inside the brackets is throwing me. Is this the means by which the local (in the subroutine) %ENV is used to overwrite the existing %ENV? I've not seen this syntax before. Ronnie Cruickshank
        Thanks, that's a great help. Bye, Ron.
      Thanks, Mr. Schwartz: that's a great shortcut. (Wow, an answer from the person who's book is on my shelf :-) Bye, Ron.
Re: RE (tilly) 1: Get default login environment
by ronbarak (Novice) on Oct 03, 2006 at 12:44 UTC
    Thanks, that's a great help. Bye, Ron.

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