Add "environment" style to variables. Allows the user to import variables directly from the environment. It should be noted that this was just an experiment. I have since found that the `-v` commandline flag is the best way to do this. The problem with environment variables here is that 1) it does not handle array data well `export blah=(1 2 3)`…

variable_env.diff

diff --git a/src/variable.cpp b/src/variable.cpp
index d60accc..b52220c 100644
--- a/src/variable.cpp
+++ b/src/variable.cpp
@@ -43,7 +43,7 @@ using namespace MathConst;
 
 #define MYROUND(a) (( a-floor(a) ) >= .5) ? ceil(a) : floor(a)
 
-enum{INDEX,LOOP,WORLD,UNIVERSE,ULOOP,STRING,FILEVAR,EQUAL,ATOM};
+enum{INDEX,LOOP,WORLD,UNIVERSE,ULOOP,STRING,FILEVAR,EQUAL,ATOM,ENVIRONMENT};
 enum{ARG,OP};
 
 // customize by adding a function
@@ -330,6 +330,27 @@ void Variable::set(int narg, char **arg)
     data[nvar] = new char*[num[nvar]];
     copy(1,&arg[2],data[nvar]);
 
+  // ENVIRONMENT
+  // remove pre-existing var if also style ENVIRONMENT (allows it to be reset)
+  // num = 1, which = 1st value
+  // data = 1 value, string to eval
+
+  } else if (strcmp(arg[1],"environment") == 0) {
+    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (find(arg[0]) >= 0) {
+      if (style[find(arg[0])] != STRING)
+        error->all(FLERR,"Cannot redefine variable as a different style");
+      remove(find(arg[0]));
+    }
+    if (nvar == maxvar) grow();
+    style[nvar] = ENVIRONMENT;
+    num[nvar] = 1;
+    which[nvar] = 0;
+    pad[nvar] = 0;
+    data[nvar] = new char*[num[nvar]];
+    arg[2] = getenv(arg[2]);
+    copy(1,&arg[2],data[nvar]);
+
   } else error->all(FLERR,"Illegal variable command");
 
   // set name of variable
@@ -389,7 +410,7 @@ int Variable::next(int narg, char **arg)
   // invalid styles STRING or EQUAL or WORLD or ATOM
 
   int istyle = style[find(arg[0])];
-  if (istyle == STRING || istyle == EQUAL || istyle == WORLD || istyle == ATOM)
+  if (istyle == STRING || istyle == EQUAL || istyle == WORLD || istyle == ATOM || istyle == ENVIRONMENT)
     error->all(FLERR,"Invalid variable style with next command");
 
   // increment all variables in list
@@ -479,7 +500,7 @@ char *Variable::retrieve(char *name)
   char *str;
   if (style[ivar] == INDEX || style[ivar] == WORLD ||
       style[ivar] == UNIVERSE || style[ivar] == STRING || 
-      style[ivar] == FILEVAR) {
+      style[ivar] == FILEVAR || style[ivar] == ENVIRONMENT) {
     str = data[ivar][which[ivar]];
   } else if (style[ivar] == LOOP || style[ivar] == ULOOP) {
     char result[16];