4 files changed, 36 insertions, 12 deletions
diff --git a/etc/environments/default-clang.bat b/etc/environments/default-clang.bat
index 769e6dd..75861ff 100644
--- a/etc/environments/default-clang.bat
+++ b/etc/environments/default-clang.bat
@@ -31,7 +31,7 @@ set "VCVARS32=VC\Auxiliary\Build\vcvarsamd64_x86.bat"
 set "VCVARS64=VC\Auxiliary\Build\vcvars64.bat"
 
 rem %1  - target
-rem %2  - bbot executable
+rem %2  - bbot executable (if absent, then run %COMSPEC%)
 rem %3+ - bbot options
 
 setlocal EnableExtensions EnableDelayedExpansion
@@ -65,8 +65,14 @@ if not "_%MSVC%_" == "__" (
   )
 )
 
-%2 %3 %4 %5 %6 %7 %8 %9 cc "config.c=%C% %MODE%" "config.cxx=%CXX% %MODE%"
-if errorlevel 1 goto error
+if not "_%2_" == "__" (
+  %2 %3 %4 %5 %6 %7 %8 %9 cc "config.c=%C% %MODE%" "config.cxx=%CXX% %MODE%"
+  if errorlevel 1 goto error
+) else (
+  echo config.c=%C% %MODE%
+  echo config.cxx=%CXX% %MODE%
+  %COMSPEC%
+)
 
 goto end
 
diff --git a/etc/environments/default-mingw.bat b/etc/environments/default-mingw.bat
index 29861a5..9adee8f 100644
--- a/etc/environments/default-mingw.bat
+++ b/etc/environments/default-mingw.bat
@@ -14,7 +14,7 @@ set "CXX=g++"
 set "MINGW=C:\build2\bin"
 
 rem %1  - target
-rem %2  - bbot executable
+rem %2  - bbot executable (if absent, then run %COMSPEC%)
 rem %3+ - bbot options
 
 setlocal EnableExtensions EnableDelayedExpansion
@@ -35,8 +35,14 @@ if "_%1_" == "_x86_64-w64-mingw32_" (
   )
 )
 
-%2 %3 %4 %5 %6 %7 %8 %9 cc "config.c=%C% %MODE%" "config.cxx=%CXX% %MODE%"
-if errorlevel 1 goto error
+if not "_%2_" == "__" (
+  %2 %3 %4 %5 %6 %7 %8 %9 cc "config.c=%C% %MODE%" "config.cxx=%CXX% %MODE%"
+  if errorlevel 1 goto error
+) else (
+  echo config.c=%C% %MODE%
+  echo config.cxx=%CXX% %MODE%
+  %COMSPEC%
+)
 
 goto end
 
diff --git a/etc/environments/default-msvc-14.bat b/etc/environments/default-msvc-14.bat
index d05e125..f5e64eb 100644
--- a/etc/environments/default-msvc-14.bat
+++ b/etc/environments/default-msvc-14.bat
@@ -11,7 +11,7 @@ set "MSVC=C:\Program Files (x86)\Microsoft Visual Studio 14.0"
 set "VCVARS=VC\vcvarsall.bat"
 
 rem %1  - target
-rem %2  - bbot executable
+rem %2  - bbot executable (if absent, then run %COMSPEC%)
 rem %3+ - bbot options
 
 setlocal EnableExtensions EnableDelayedExpansion
@@ -32,8 +32,14 @@ if "_%1_" == "_x86_64-microsoft-win32-msvc14.0_" (
 call "%MSVC%\%VCVARS%" %VCARCH%
 if errorlevel 1 goto error
 
-%2 %3 %4 %5 %6 %7 %8 %9 cc config.c=cl config.cxx=cl
-if errorlevel 1 goto error
+if not "_%2_" == "__" (
+  %2 %3 %4 %5 %6 %7 %8 %9 cc config.c=cl config.cxx=cl
+  if errorlevel 1 goto error
+) else (
+  echo config.c=cl
+  echo config.cxx=cl
+  %COMSPEC%
+)
 
 goto end
 
diff --git a/etc/environments/default-msvc.bat b/etc/environments/default-msvc.bat
index 670b3a8..563a81a 100644
--- a/etc/environments/default-msvc.bat
+++ b/etc/environments/default-msvc.bat
@@ -24,7 +24,7 @@ set "VCVARS32=VC\Auxiliary\Build\vcvarsamd64_x86.bat"
 set "VCVARS64=VC\Auxiliary\Build\vcvars64.bat"
 
 rem %1  - target
-rem %2  - bbot executable
+rem %2  - bbot executable (if absent, then run %COMSPEC%)
 rem %3+ - bbot options
 
 setlocal EnableExtensions EnableDelayedExpansion
@@ -54,8 +54,14 @@ if not "_%MSVC%_" == "__" (
   )
 )
 
-%2 %3 %4 %5 %6 %7 %8 %9 cc config.c=cl config.cxx=cl
-if errorlevel 1 goto error
+if not "_%2_" == "__" (
+  %2 %3 %4 %5 %6 %7 %8 %9 cc config.c=cl config.cxx=cl
+  if errorlevel 1 goto error
+) else (
+  echo config.c=cl
+  echo config.cxx=cl
+  %COMSPEC%
+)
 
 goto end