diff --git a/compiler/cgen.v b/compiler/cgen.v
index 740924e6e1..708a0c9ea3 100644
--- a/compiler/cgen.v
+++ b/compiler/cgen.v
@@ -261,7 +261,10 @@ fn build_thirdparty_obj_file(flag string) {
 		} 
 	} 
 	cc := if os.user_os() == 'windows' { 'gcc' } else { 'cc' } // TODO clang support on Windows  
-	res := os.exec('$cc -fPIC -c -o $obj_path $cfiles') 
+	res := os.exec('$cc -fPIC -c -o $obj_path $cfiles') or {
+		panic(err)
+		return // TODO remove return
+	}
 	println(res) 
 } 
 
diff --git a/compiler/main.v b/compiler/main.v
index 887c9acd67..4aaa3af319 100644
--- a/compiler/main.v
+++ b/compiler/main.v
@@ -137,11 +137,17 @@ fn main() {
 			println('Building vget...') 
 			os.chdir(vroot + '/tools') 
 			vexec := os.args[0] 
-			os.exec('$vexec vget.v') 
+			_ := os.exec('$vexec vget.v') or {
+				panic(err)
+				return // TODO remove return
+			}
 			println('Done.') 
 		} 
 		println('Installing module ${mod}...') 
-		os.exec('$vget $mod') 
+		_ := os.exec('$vget $mod') or {
+			panic(err)
+			return // TODO remove return
+		}
 		return 
 	} 
 	// TODO quit if the compiler is too old 
@@ -871,7 +877,19 @@ mut args := ''
 	}
 	// Run
 	ticks := time.ticks() 
-	res := os.exec(cmd)
+	_ := os.exec(cmd) or {
+		if v.pref.is_debug {
+			println(err)
+		} else {
+			print(err.limit(200))
+			if err.len > 200 {
+				println('...\n(Use `v -debug` to print the entire error message)\n')
+			}
+		}
+		panic('C error. This should never happen. ' +
+			'Please create a GitHub issue: https://github.com/vlang/v/issues/new/choose')
+		return // TODO remove return
+	}
 	diff := time.ticks() - ticks 
 	// Print the C command
 	if v.pref.show_c_cmd || v.pref.is_verbose {
@@ -880,18 +898,6 @@ mut args := ''
 		println('cc took $diff ms') 
 		println('=========\n')
 	}
-	if res.contains('error: ') {
-		if v.pref.is_debug { 
-			println(res)
-		} else {
-			print(res.limit(200)) 
-			if res.len > 200 { 
-				println('...\n(Use `v -debug` to print the entire error message)\n')   
-			} 
-		} 
-		panic('C error. This should never happen. ' +
-			'Please create a GitHub issue: https://github.com/vlang/v/issues/new/choose')
-	}
 	// Link it if we are cross compiling and need an executable
 	if v.os == .linux && !linux_host && v.pref.build_mode != .build {
 		v.out_name = v.out_name.replace('.o', '')
@@ -905,11 +911,11 @@ mut args := ''
 		'/usr/lib/x86_64-linux-gnu/crti.o ' +
 		obj_file +
 		' /usr/lib/x86_64-linux-gnu/libc.so ' +
-		'/usr/lib/x86_64-linux-gnu/crtn.o')
-		println(ress)
-		if ress.contains('error:') {
-			exit(1)
+		'/usr/lib/x86_64-linux-gnu/crtn.o') or {
+			panic(err)
+			return // TODO remove return
 		}
+		println(ress)
 		println('linux cross compilation done. resulting binary: "$v.out_name"')
 	}
 	if !v.pref.is_debug && v.out_name_c != 'v.c' && v.out_name_c != 'v_macos.c' {
@@ -1315,22 +1321,13 @@ fn run_repl() []string {
 		if line.starts_with('print') {
 			source_code := lines.join('\n') + '\n' + line 
 			os.write_file(file, source_code)
-			s := os.exec('$vexe run $file -repl')
-			mut vals := s.split('\n')
-			if s.contains('panic: ') {
-				if !s.contains('declared and not used') 	{
-					for i:=1; i<vals.len; i++ {
-						println(vals[i])
-					} 
-				}
-				else {
-					println(s)
-				}
+			s := os.exec('$vexe run $file -repl') or {
+				panic(err)
+				break // TODO remove break
 			}
-			else {
-				for i:=0; i < vals.len; i++ {
-					println(vals[i])
-				}
+			vals := s.split('\n')
+			for i:=0; i < vals.len; i++ {
+				println(vals[i])
 			}
 		}
 		else {
@@ -1342,24 +1339,14 @@ fn run_repl() []string {
 			}
 			temp_source_code := lines.join('\n') + '\n' + temp_line
 			os.write_file(temp_file, temp_source_code)
-			s := os.exec('$vexe run $temp_file -repl')
-			if s.contains('panic: ') {
-				if !s.contains('declared and not used') 	{
-					mut vals := s.split('\n')
-					for i:=0; i < vals.len; i++ {
-						println(vals[i])
-					} 
-				}
-				else {
-					lines << line
-				}
+			s := os.exec('$vexe run $temp_file -repl') or {
+				panic(err)
+				break // TODO remove break
 			}
-			else {
-				lines << line
-				vals := s.split('\n')
-				for i:=0; i<vals.len-1; i++ {
-					println(vals[i])
-				} 
+			lines << line
+			vals := s.split('\n')
+			for i:=0; i<vals.len-1; i++ {
+				println(vals[i])
 			}
 		}
 	}
@@ -1418,15 +1405,24 @@ fn env_vflags_and_os_args() []string {
 fn update_v() {
 	println('Updating V...') 
 	vroot := os.dir(os.executable()) 
-	mut s := os.exec('git -C "$vroot" pull --rebase origin master') 
+	s := os.exec('git -C "$vroot" pull --rebase origin master') or {
+		panic(err)
+		return // TODO remove return
+	}
 	println(s) 
 	$if windows { 
 		os.mv('$vroot/v.exe', '$vroot/v_old.exe') 
-		s = os.exec('$vroot/make.bat') 
-		println(s) 
+		s2 := os.exec('$vroot/make.bat') or {
+			panic(err)
+			return // TODO remove return
+		}
+		println(s2) 
 	} $else { 
-		s = os.exec('make -C "$vroot"') 
-		println(s) 
+		s2 := os.exec('make -C "$vroot"') or {
+			panic(err)
+			return // TODO remove return
+		}
+		println(s2) 
 	} 
 } 
 
diff --git a/compiler/msvc_win.v b/compiler/msvc_win.v
index 8cdc6da49a..5db91d0b4b 100644
--- a/compiler/msvc_win.v
+++ b/compiler/msvc_win.v
@@ -134,7 +134,10 @@ fn find_vs() ?VsInstallation {
 	// VSWhere is guaranteed to be installed at this location now
 	// If its not there then end user needs to update their visual studio 
 	// installation!
-	res := os.exec('""%ProgramFiles(x86)%\\Microsoft Visual Studio\\Installer\\vswhere.exe" -latest -products * -requires Microsoft.VisualStudio.Component.VC.Tools.x86.x64 -property installationPath"')
+	res := os.exec('""%ProgramFiles(x86)%\\Microsoft Visual Studio\\Installer\\vswhere.exe" -latest -products * -requires Microsoft.VisualStudio.Component.VC.Tools.x86.x64 -property installationPath"') or {
+		panic(err)
+		return error(err)// TODO remove return
+	}
 	// println('res: "$res"')
 
 	version := os.read_file('$res\\VC\\Auxiliary\\Build\\Microsoft.VCToolsVersion.default.txt') or {
@@ -341,13 +344,13 @@ pub fn (v mut V) cc_msvc() {
 
 	// println('$cmd')
 
-	res := os.exec(cmd)
+	_ := os.exec(cmd) or {
+		println(err)
+		panic('msvc error')
+		return // TODO remove return
+	}
 	// println(res)
 	// println('C OUTPUT:')
-	if res.contains('error') {
-		println(res)
-		panic('msvc error')
-	}
 
 	if !v.pref.is_debug && v.out_name_c != 'v.c' && v.out_name_c != 'v_macos.c' {
 		os.rm('.$v.out_name_c') 
@@ -386,7 +389,10 @@ fn build_thirdparty_obj_file_with_msvc(flag string) {
 
 	println('$cfiles')
 
-	res := os.exec('""$msvc.exe_path\\cl.exe" /volatile:ms /Z7 $include_string /c $cfiles /Fo"$obj_path" /D_UNICODE /DUNICODE"')
+	res := os.exec('""$msvc.exe_path\\cl.exe" /volatile:ms /Z7 $include_string /c $cfiles /Fo"$obj_path" /D_UNICODE /DUNICODE"') or {
+		panic(err)
+		return // TODO remove return
+	}
 	println(res)
 } 
 
diff --git a/make_tests.bat b/make_tests.bat
index e79ec2ecb6..06967ff71a 100644
--- a/make_tests.bat
+++ b/make_tests.bat
@@ -31,6 +31,7 @@ for /r . %%x in (*_test.v) do (
 goto :done
 
 :fail
+echo fail
 exit /b 1
 
 :done
diff --git a/tools/vget.v b/tools/vget.v
index 29e0c9df12..4b147bb5cf 100644
--- a/tools/vget.v
+++ b/tools/vget.v
@@ -36,6 +36,9 @@ fn main() {
 	os.mkdir('.vmodules') 
 	println('Done.') 
 	} 
-	os.exec('git -C "$home/.vmodules" clone --depth=1 $mod.url ' + mod.name.replace('.', '/'))
+	_ := os.exec('git -C "$home/.vmodules" clone --depth=1 $mod.url ' + mod.name.replace('.', '/')) or {
+		panic(err)
+		return // TODO remove return
+	}
 	println(s) 
 } 
diff --git a/vlib/os/os.v b/vlib/os/os.v
index ff3d56d21f..d64723a2b1 100644
--- a/vlib/os/os.v
+++ b/vlib/os/os.v
@@ -336,21 +336,33 @@ fn popen(path string) *FILE {
 	}
 }
 
+fn pclose(f *FILE) int {
+	$if windows {
+		return C._pclose(f)
+	}
+	$else {
+		return C.pclose(f)
+	}
+}
+
 // exec starts the specified command, waits for it to complete, and returns its output.
-pub fn exec(_cmd string) string {
+pub fn exec(_cmd string) ?string {
 	cmd := '$_cmd 2>&1'
 	f := popen(cmd)
 	if isnil(f) {
-		// TODO optional or error code 
-		println('popen $cmd failed')
-		return '' 
+		return error('popen $cmd failed')
 	}
 	buf := [1000]byte 
 	mut res := ''
 	for C.fgets(buf, 1000, f) != 0 { 
 		res += tos(buf, strlen(buf)) 
 	}
-	return res.trim_space()
+	res = res.trim_space()
+	status_code := pclose(f)/256
+	if status_code != 0 {
+		return error(res)
+	}
+	return res
 }
 
 // `getenv` returns the value of the environment variable named by the key.