diff --git a/Source/cmEnvironment.cxx b/Source/cmEnvironment.cxx
index 9cc9bc7868..8832c56542 100644
--- a/Source/cmEnvironment.cxx
+++ b/Source/cmEnvironment.cxx
@@ -2,12 +2,16 @@
    file LICENSE.rst or https://cmake.org/licensing for details.  */
 #include "cmEnvironment.h"
 
+#include <set>
 #include <utility>
 
 #include <cm/string_view>
 #include <cm/vector>
 #include <cmext/algorithm>
 
+#include "cmStringAlgorithms.h"
+#include "cmSystemTools.h"
+
 #if defined(_WIN32)
 #  include "cmsys/String.h"
 #endif
@@ -64,3 +68,138 @@ std::vector<std::string> cmEnvironment::GetVariables() const
   }
   return result;
 }
+
+namespace {
+
+auto const ValidOperators = std::set<cm::string_view>{
+  "set",
+  "unset",
+  "string_append",
+  "string_prepend",
+  "path_list_append",
+  "path_list_prepend",
+  "cmake_list_append",
+  "cmake_list_prepend",
+};
+
+struct ListAppend
+{
+public:
+  ListAppend(std::string val, char sep)
+    : value(std::move(val))
+    , separator(sep)
+  {
+  }
+
+  void operator()(std::string& output) const
+  {
+    if (!output.empty()) {
+      output += separator;
+    }
+    output += value;
+  }
+
+private:
+  std::string value;
+  char separator;
+};
+
+struct ListPrepend
+{
+public:
+  ListPrepend(std::string val, char sep)
+    : value(std::move(val))
+    , separator(sep)
+  {
+  }
+
+  void operator()(std::string& output) const
+  {
+    if (!output.empty()) {
+      output.insert(output.begin(), separator);
+    }
+    output.insert(0, value);
+  }
+
+private:
+  std::string value;
+  char separator;
+};
+
+} // namespace
+
+bool cmEnvironmentModification::Add(std::vector<std::string> const& envmod)
+{
+  bool ok = true;
+  for (auto const& entry : envmod) {
+    ok &= this->Add(entry);
+  }
+  return ok;
+}
+
+bool cmEnvironmentModification::Add(std::string const& envmod)
+{
+  // Split on `=`
+  auto const eq_loc = envmod.find_first_of('=');
+  if (eq_loc == std::string::npos) {
+    cmSystemTools::Error(cmStrCat(
+      "Error: Missing `=` after the variable name in: ", envmod, '\n'));
+    return false;
+  }
+
+  // Split operation on `:`
+  auto const op_value_start = eq_loc + 1;
+  auto const colon_loc = envmod.find_first_of(':', op_value_start);
+  if (colon_loc == std::string::npos) {
+    cmSystemTools::Error(
+      cmStrCat("Error: Missing `:` after the operation in: ", envmod, '\n'));
+    return false;
+  }
+
+  auto entry = Entry{};
+  entry.Name = envmod.substr(0, eq_loc);
+  entry.Op = envmod.substr(op_value_start, colon_loc - op_value_start);
+  entry.Value = envmod.substr(colon_loc + 1);
+
+  if (entry.Op == "reset") {
+    cm::erase_if(this->Entries,
+                 [&entry](Entry const& e) { return e.Name == entry.Name; });
+    return true;
+  }
+
+  if (!cm::contains(ValidOperators, entry.Op)) {
+    cmSystemTools::Error(cmStrCat(
+      "Error: Unrecognized environment manipulation argument: ", entry.Op,
+      '\n'));
+    return false;
+  }
+
+  this->Entries.push_back(std::move(entry));
+  return true;
+}
+
+void cmEnvironmentModification::ApplyTo(cmEnvironment& env)
+{
+  char const path_sep = cmSystemTools::GetSystemPathlistSeparator();
+
+  for (auto const& e : this->Entries) {
+    if (e.Op == "set") {
+      env.PutEnv(e.Name + "=" + e.Value);
+    } else if (e.Op == "unset") {
+      env.UnPutEnv(e.Name);
+    } else if (e.Op == "string_append") {
+      env.Modify(e.Name, [&e](std::string& output) { output += e.Value; });
+    } else if (e.Op == "string_prepend") {
+      env.Modify(e.Name,
+                 [&e](std::string& output) { output.insert(0, e.Value); });
+    } else if (e.Op == "path_list_append") {
+      env.Modify(e.Name, ListAppend(e.Value, path_sep));
+    } else if (e.Op == "path_list_prepend") {
+      env.Modify(e.Name, ListPrepend(e.Value, path_sep));
+    } else if (e.Op == "cmake_list_append") {
+      env.Modify(e.Name, ListAppend(e.Value, ';'));
+    } else if (e.Op == "cmake_list_prepend") {
+      env.Modify(e.Name, ListPrepend(e.Value, ';'));
+    }
+  }
+}
diff --git a/Source/cmEnvironment.h b/Source/cmEnvironment.h
index 5ceaa857eb..700b7ac897 100644
--- a/Source/cmEnvironment.h
+++ b/Source/cmEnvironment.h
@@ -53,3 +53,22 @@ protected:
   };
   std::map<std::string, cm::optional<std::string>, EnvNameLess> Map;
 };
+
+class cmEnvironmentModification
+{
+public:
+  bool Add(std::string const& envmod);
+  bool Add(std::vector<std::string> const& envmod);
+
+  void ApplyTo(cmEnvironment& env);
+
+private:
+  struct Entry
+  {
+    std::string Name;
+    std::string Value;
+    std::string Op;
+  };
+
+  std::vector<Entry> Entries;
+};