lang: Add getenv function

$x = getenv("NAME")
    $y = defaultenv("NOTEXIST", "defaultvalue")
    $z = hasenv("NAME")
    $a = env()
    $b = maplookup($a, "NAME", "defaultvalue")

examples/lang/env0.mcl

@@ -0,0 +1,20 @@
+# read and print environment variable
+# env TEST=123 EMPTY= ./mgmt run --tmp-prefix --lang=examples/lang/env0.mcl --converged-timeout=5
+
+$x = getenv("TEST", "321")
+
+print "print1" {
+	msg => printf("the value of the environment variable TEST is: %s", $x),
+}
+
+$y = getenv("DOESNOTEXIT", "321")
+
+print "print2" {
+	msg => printf("environment variable DOESNOTEXIT does not exist, defaulting to: %s", $y),
+}
+
+$z = getenv("EMPTY", "456")
+
+print "print3" {
+	msg => printf("same goes for epmty variables like EMPTY: %s", $z),
+}

lang/funcs/simple/env_func.go

@@ -0,0 +1,84 @@
+// Mgmt
+// Copyright (C) 2013-2018+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package simple // TODO: should this be in its own individual package?
+
+import (
+	"os"
+	"strings"
+
+	"github.com/purpleidea/mgmt/lang/types"
+)
+
+func init() {
+	Register("getenv", &types.FuncValue{
+		T: types.NewType("func(str) str"),
+		V: GetEnv,
+	})
+	Register("defaultenv", &types.FuncValue{
+		T: types.NewType("func(str, str) str"),
+		V: DefaultEnv,
+	})
+	Register("hasenv", &types.FuncValue{
+		T: types.NewType("func(str) bool"),
+		V: HasEnv,
+	})
+	Register("env", &types.FuncValue{
+		T: types.NewType("func() {str: str}"),
+		V: Env,
+	})
+}
+
+// GetEnv gets environment variable by name or returns empty string if non existing.
+func GetEnv(input []types.Value) (types.Value, error) {
+	return &types.StrValue{
+		V: os.Getenv(input[0].Str()),
+	}, nil
+}
+
+// DefaultEnv gets environment variable by name or returns default if non existing.
+func DefaultEnv(input []types.Value) (types.Value, error) {
+	value, exists := os.LookupEnv(input[0].Str())
+	if !exists {
+		value = input[1].Str()
+	}
+	return &types.StrValue{
+		V: value,
+	}, nil
+}
+
+// HasEnv returns true if environment variable exists.
+func HasEnv(input []types.Value) (types.Value, error) {
+	_, exists := os.LookupEnv(input[0].Str())
+	return &types.BoolValue{
+		V: exists,
+	}, nil
+}
+
+// Env returns a map of all keys and their values.
+func Env(input []types.Value) (types.Value, error) {
+	environ := make(map[types.Value]types.Value)
+	for _, keyval := range os.Environ() {
+		if i := strings.IndexRune(keyval, '='); i != -1 {
+			environ[&types.StrValue{V: keyval[:i]}] = &types.StrValue{V: keyval[i+1:]}
+		}
+	}
+	return &types.MapValue{
+		T: types.NewType("{str: str}"),
+		V: environ,
+	}, nil
+}

test/shell/env0.mcl

@@ -0,0 +1,19 @@
+$tmpdir = defaultenv("TMPDIR", "/tmp")
+
+$x = getenv("TEST")
+$y = getenv("DOESNOTEXIST")
+$z = getenv("EMPTY")
+
+$a = defaultenv("TEST", "321")
+$b = defaultenv("DOESNOTEXIST", "321")
+$c = defaultenv("EMPTY", "456")
+
+$t = hasenv("TEST")
+$f = hasenv("DOESNOTEXIST")
+
+$env = env()
+$m = maplookup($env, "TEST", "321")
+
+file "${tmpdir}/environ" {
+	content => printf("%s,%s,%s:%s,%s,%s:%t,%t:%s", $x, $y, $z, $a, $b, $c, $t, $f, $m),
+}

test/shell/env0.sh

@@ -0,0 +1,21 @@
+#!/bin/bash -e
+
+set -o errexit
+set -o pipefail
+
+. ../util.sh
+
+# these values represent environment variable values below or defaults set in test/shell/env0.mcl
+regex="123,,:123,321,:true,false:123"
+
+tmpdir="$($mktemp --tmpdir -d tmp.XXX)"
+
+env TMPDIR="${tmpdir}" TEST=123 EMPTY="" $timeout -sKILL 60s "$MGMT" run --tmp-prefix --converged-timeout=5 --lang env0.mcl
+e=$?
+
+egrep "$regex" "$tmpdir/environ" || fail_test "Could not match '$(cat "$tmpdir/environ")' in '$tmpdir/environ' to '$regex'."
+
+# cleanup if everything went well
+rm -r "$tmpdir"
+
+exit $e