add is_os() special function to the variable command

doc/src/variable.rst

@@ -66,7 +66,7 @@ Syntax
                            bound(group,dir,region), gyration(group,region), ke(group,reigon),
                            angmom(group,dim,region), torque(group,dim,region),
                            inertia(group,dimdim,region), omega(group,dim,region)
-         special functions = sum(x), min(x), max(x), ave(x), trap(x), slope(x), gmask(x), rmask(x), grmask(x,y), next(x), is_file(name), extract_setting(name)
+         special functions = sum(x), min(x), max(x), ave(x), trap(x), slope(x), gmask(x), rmask(x), grmask(x,y), next(x), is_file(name), is_os(name), extract_setting(name)
          feature functions = is_active(category,feature), is_available(category,feature), is_defined(category,id)
          atom value = id[i], mass[i], type[i], mol[i], x[i], y[i], z[i], vx[i], vy[i], vz[i], fx[i], fy[i], fz[i], q[i]
          atom vector = id, mass, type, mol, x, y, z, vx, vy, vz, fx, fy, fz, q
@@ -939,6 +939,20 @@ The is_file(name) function is a test whether *name* is a (readable) file
 and returns 1 in this case, otherwise it returns 0.  For that *name*
 is taken as a literal string and must not have any blanks in it.
 
+The is_os(name) function is a test whether *name* is part of the OS
+information that LAMMPS collects and provides in the
+:cpp:func:`platform::os_info() <LAMMPS_NS::platform::os_info>` function.
+The argument *name* is interpreted as a regular expression as documented
+for the :cpp:func:`utils::strmatch() <LAMMPS_NS::utils::strmatch>`
+function. This allows to adapt LAMMPS inputs to the OS it runs on:
+
+.. code-block:: LAMMPS
+
+   if $(is_os(^Windows)) then &
+     "shell copy ${input_dir}/some_file.txt ." &
+   else &
+     "shell cp ${input_dir}/some_file.txt ."
+
 The extract_setting(name) function enables access to basic settings for
 the LAMMPS executable and the running simulation via calling the
 :cpp:func:`lammps_extract_setting` library function.  For example, the

src/variable.cpp

@@ -3942,7 +3942,7 @@ int Variable::special_function(char *word, char *contents, Tree **tree, Tree **t
       strcmp(word,"trap") != 0 && strcmp(word,"slope") != 0 && strcmp(word,"gmask") != 0 && strcmp(word,"rmask") != 0 &&
       strcmp(word,"grmask") != 0 && strcmp(word,"next") != 0 && strcmp(word,"is_active") != 0 &&
       strcmp(word,"is_defined") != 0 && strcmp(word,"is_available") != 0 && strcmp(word,"is_file") != 0 &&
-      strcmp(word,"extract_setting") != 0)
+      strcmp(word,"is_os") != 0 && strcmp(word,"extract_setting") != 0)
     return 0;
 
   // parse contents for comma-separated args
@@ -4340,6 +4340,19 @@ int Variable::special_function(char *word, char *contents, Tree **tree, Tree **t
       treestack[ntreestack++] = newtree;
     } else argstack[nargstack++] = value;
 
+  } else if (strcmp(word,"is_os") == 0) {
+    if (narg != 1) print_var_error(FLERR,"Invalid is_os() function in variable formula",ivar);
+    value = utils::strmatch(platform::os_info(), args[0]) ? 1.0 : 0.0;
+
+    // save value in tree or on argstack
+
+    if (tree) {
+      auto newtree = new Tree();
+      newtree->type = VALUE;
+      newtree->value = value;
+      treestack[ntreestack++] = newtree;
+    } else argstack[nargstack++] = value;
+
   } else if (strcmp(word,"extract_setting") == 0) {
     if (narg != 1) print_var_error(FLERR,"Invalid extract_setting() function in variable formula",ivar);
 

unittest/commands/test_variables.cpp

@@ -144,12 +144,14 @@ TEST_F(VariableTest, CreateDelete)
     command("variable ten3   uloop     4 pad");
     command("variable dummy  index     0");
     command("variable file   equal     is_file(MYFILE)");
+    command("variable iswin  equal     is_os(^Windows)");
+    command("variable islin  equal     is_os(^Linux)");
     END_HIDE_OUTPUT();
-    ASSERT_EQ(variable->nvar, 18);
+    ASSERT_EQ(variable->nvar, 20);
     BEGIN_HIDE_OUTPUT();
     command("variable dummy  delete");
     END_HIDE_OUTPUT();
-    ASSERT_EQ(variable->nvar, 17);
+    ASSERT_EQ(variable->nvar, 19);
     ASSERT_THAT(variable->retrieve("three"), StrEq("three"));
     variable->set_string("three", "four");
     ASSERT_THAT(variable->retrieve("three"), StrEq("four"));
@@ -168,6 +170,17 @@ TEST_F(VariableTest, CreateDelete)
     platform::unlink("MYFILE");
     ASSERT_THAT(variable->retrieve("file"), StrEq("0"));
 
+#if defined(_WIN32)
+    ASSERT_THAT(variable->retrieve("iswin"), StrEq("1"));
+    ASSERT_THAT(variable->retrieve("islin"), StrEq("0"));
+#elif defined(__linux__)
+    ASSERT_THAT(variable->retrieve("iswin"), StrEq("0"));
+    ASSERT_THAT(variable->retrieve("islin"), StrEq("1"));
+#else
+    ASSERT_THAT(variable->retrieve("iswin"), StrEq("0"));
+    ASSERT_THAT(variable->retrieve("islin"), StrEq("0"));
+#endif
+
     BEGIN_HIDE_OUTPUT();
     command("variable seven delete");
     command("variable seven getenv TEST_VARIABLE");