diff --git a/src/V3EmitCFunc.h b/src/V3EmitCFunc.h
index 8dbe3ca70..f9b3bd3d6 100644
--- a/src/V3EmitCFunc.h
+++ b/src/V3EmitCFunc.h
@@ -636,7 +636,7 @@ public:
                 puts("vlSymsp->_traceDumpOpen();\n");
             } else {
                 puts("VL_PRINTF_MT(\"-Info: ");
-                puts(protect(nodep->fileline()->filename()));
+                puts(V3OutFormatter::quoteNameControls(protect(nodep->fileline()->filename())));
                 puts(":");
                 puts(cvtToStr(nodep->fileline()->lineno()));
                 puts(": $dumpvar ignored, as Verilated without --trace");
diff --git a/src/V3EmitCMake.cpp b/src/V3EmitCMake.cpp
index 6598da9a8..bd065144d 100644
--- a/src/V3EmitCMake.cpp
+++ b/src/V3EmitCMake.cpp
@@ -43,15 +43,11 @@ class CMakeEmitter final {
     template <typename List>
     static string cmake_list(const List& strs) {
         string s;
-        if (strs.begin() != strs.end()) {
-            s.append("\"");
-            s.append(VString::quoteAny(*strs.begin(), '"', '\\'));
-            s.append("\"");
-            for (typename List::const_iterator it = ++strs.begin(); it != strs.end(); ++it) {
-                s.append(" \"");
-                s.append(VString::quoteAny(*it, '"', '\\'));
-                s.append("\"");
-            }
+        for (auto it = strs.begin(); it != strs.end(); ++it) {
+            s += '"';
+            s += V3OutFormatter::quoteNameControls(*it);
+            s += '"';
+            if (it != strs.end()) s += ' ';
         }
         return s;
     }
@@ -63,13 +59,13 @@ class CMakeEmitter final {
     static void cmake_set_raw(std::ofstream& of, const string& name, const string& raw_value,
                               const string& cache_type = "", const string& docstring = "") {
         of << "set(" << name << " " << raw_value;
-        if (!cache_type.empty()) of << " CACHE " << cache_type << " \"" << docstring << "\"";
+        if (!cache_type.empty()) of << " CACHE " << cache_type << " \"" << docstring << '"';
         of << ")\n";
     }
 
     static void cmake_set(std::ofstream& of, const string& name, const string& value,
                           const string& cache_type = "", const string& docstring = "") {
-        const string raw_value = "\"" + value + "\"";
+        const string raw_value = '"' + value + '"';
         cmake_set_raw(of, name, raw_value, cache_type, docstring);
     }
 
@@ -88,9 +84,10 @@ class CMakeEmitter final {
         *of << "# which becomes available after executing `find_package(verilator).\n";
 
         *of << "\n### Constants...\n";
-        cmake_set(*of, "PERL", V3Options::getenvPERL(), "FILEPATH",
-                  "Perl executable (from $PERL)");
-        cmake_set(*of, "VERILATOR_ROOT", V3Options::getenvVERILATOR_ROOT(), "PATH",
+        cmake_set(*of, "PERL", V3OutFormatter::quoteNameControls(V3Options::getenvPERL()),
+                  "FILEPATH", "Perl executable (from $PERL)");
+        cmake_set(*of, "VERILATOR_ROOT",
+                  V3OutFormatter::quoteNameControls(V3Options::getenvVERILATOR_ROOT()), "PATH",
                   "Path to Verilator kit (from $VERILATOR_ROOT)");
 
         *of << "\n### Compiler flags...\n";
diff --git a/src/V3EmitMk.cpp b/src/V3EmitMk.cpp
index 3f38e5119..bdf088c6a 100644
--- a/src/V3EmitMk.cpp
+++ b/src/V3EmitMk.cpp
@@ -154,9 +154,10 @@ public:
         }
         of.puts("\n### Constants...\n");
         of.puts("# Perl executable (from $PERL)\n");
-        of.puts("PERL = " + V3Options::getenvPERL() + "\n");
+        of.puts("PERL = " + V3OutFormatter::quoteNameControls(V3Options::getenvPERL()) + "\n");
         of.puts("# Path to Verilator kit (from $VERILATOR_ROOT)\n");
-        of.puts("VERILATOR_ROOT = " + V3Options::getenvVERILATOR_ROOT() + "\n");
+        of.puts("VERILATOR_ROOT = "
+                + V3OutFormatter::quoteNameControls(V3Options::getenvVERILATOR_ROOT()) + "\n");
         of.puts("# SystemC include directory with systemc.h (from $SYSTEMC_INCLUDE)\n");
         of.puts(string{"SYSTEMC_INCLUDE ?= "} + V3Options::getenvSYSTEMC_INCLUDE() + "\n");
         of.puts("# SystemC library directory with libsystemc.a (from $SYSTEMC_LIBDIR)\n");
diff --git a/src/V3Error.cpp b/src/V3Error.cpp
index 5d915f9c5..1194cd7e3 100644
--- a/src/V3Error.cpp
+++ b/src/V3Error.cpp
@@ -16,6 +16,7 @@
 
 // clang-format off
 #include "V3Error.h"
+#include "V3Os.h"
 #ifndef V3ERROR_NO_GLOBAL_
 # include "V3Ast.h"
 # include "V3Global.h"
@@ -262,13 +263,8 @@ void V3Error::init() {
 
 string V3Error::lineStr(const char* filename, int lineno) VL_PURE {
     std::ostringstream out;
-    const char* const fnslashp = std::strrchr(filename, '/');
-    if (fnslashp) filename = fnslashp + 1;
-    out << filename << ":" << std::dec << lineno << ":";
-    const char* const spaces = "                    ";
-    size_t numsp = out.str().length();
-    if (numsp > 20) numsp = 20;
-    out << (spaces + numsp);
+    out << V3Os::filenameNonDir(filename) << ":" << std::dec << lineno << ":";
+    out << std::string(std::max<int>(0, 20 - static_cast<int>(out.str().length())), ' ');
     return out.str();
 }
 
diff --git a/src/V3File.cpp b/src/V3File.cpp
index 157e8d028..7a669f30d 100644
--- a/src/V3File.cpp
+++ b/src/V3File.cpp
@@ -859,7 +859,7 @@ void V3OutFormatter::putcNoTracking(char chr) {
 string V3OutFormatter::quoteNameControls(const string& namein,
                                          V3OutFormatter::Language lang) VL_PURE {
     // Encode control chars into output-appropriate escapes
-    // Reverse is V3Parse::deQuote
+    // Reverse is VString::unquoteSVString
     string out;
     if (lang == LA_XML) {
         // Encode chars into XML string
diff --git a/src/V3FileLine.cpp b/src/V3FileLine.cpp
index e97db97b2..a8bf044a6 100644
--- a/src/V3FileLine.cpp
+++ b/src/V3FileLine.cpp
@@ -203,63 +203,62 @@ string FileLine::xmlDetailedLocation() const {
 }
 
 string FileLine::lineDirectiveStrg(int enterExit) const {
-    return std::string{"`line "} + cvtToStr(lastLineno()) + " \"" + filename() + "\" "
-           + cvtToStr(enterExit) + "\n";
+    return std::string{"`line "} + cvtToStr(lastLineno()) + " \""
+           + V3OutFormatter::quoteNameControls(filename()) + "\" " + cvtToStr(enterExit) + "\n";
 }
 
 void FileLine::lineDirective(const char* textp, int& enterExitRef) {
     // Handle `line directive
     // Does not parse streamNumber/streamLineno as the next input token
     // will come from the same stream as the previous line.
+    do {
+        int lineNo;
+        // Skip `line
+        while (*textp && std::isspace(*textp)) ++textp;
+        while (*textp && !std::isspace(*textp)) ++textp;
+        while (*textp && std::isspace(*textp)) ++textp;
 
-    // Skip `line
-    while (*textp && std::isspace(*textp)) ++textp;
-    while (*textp && !std::isspace(*textp)) ++textp;
-    while (*textp && (std::isspace(*textp) || *textp == '"')) ++textp;
+        // Grab linenumber
+        const char* const ln = textp;
+        while (*textp && !std::isspace(*textp)) ++textp;
+        if (0 == strncmp(ln, "`__LINE__", textp - ln)) {
+            // Special case - see docs - don't change other than accounting for `line itself
+            lineNo = lineno() + 1;
+        } else if (std::isdigit(*ln)) {
+            lineNo = std::atoi(ln);
+        } else {
+            break;  // Fail
+        }
+        lineno(lineNo);
+        while (*textp && (std::isspace(*textp))) ++textp;
 
-    // Grab linenumber
-    bool fail = false;
-    const char* const ln = textp;
-    while (*textp && !std::isspace(*textp)) ++textp;
-    if (0 == strncmp(ln, "`__LINE__", strlen("`__LINE__"))) {
-        // Special case - see docs - don't change other than accounting for `line itself
-        lineno(lineno() + 1);
-    }
-    if (std::isdigit(*ln)) {
-        lineno(std::atoi(ln));
-    } else {
-        fail = true;
-    }
-    while (*textp && (std::isspace(*textp))) ++textp;
-    if (*textp != '"') fail = true;
-    while (*textp && (std::isspace(*textp) || *textp == '"')) ++textp;
+        // Grab filename
+        if (*textp != '"') break;  // Fail
+        const char* const fn = ++textp;
+        while (*textp && *textp != '"') ++textp;
+        if (*textp != '"') break;  // Fail
+        string errMsg;
+        const string& parsedFilename = VString::unquoteSVString(string{fn, textp}, errMsg);
+        if (!errMsg.empty()) this->v3error(errMsg.c_str());
+        filename(parsedFilename);
+        ++textp;
+        while (*textp && std::isspace(*textp)) ++textp;
 
-    // Grab filename
-    const char* const fn = textp;
-    while (*textp && !(std::isspace(*textp) || *textp == '"')) ++textp;
-    if (textp != fn) {
-        string strfn = fn;
-        strfn = strfn.substr(0, textp - fn);
-        filename(strfn);
-    } else {
-        fail = true;
-    }
+        // Grab level
+        if (!std::isdigit(*textp)) break;  // Fail
+        const int level = std::atoi(textp);
+        if (level < 0 || level >= 3) break;  // Fail
+        /// TODO: store lineno/filename only when the `line directive is valid
+        /// lineno(lineNo);
+        /// filename(filenameNew);
+        enterExitRef = level;
+        return;
+    } while (false);
 
-    // Grab level
-    while (*textp && (std::isspace(*textp) || *textp == '"')) ++textp;
-    if (std::isdigit(*textp)) {
-        enterExitRef = std::atoi(textp);
-        if (enterExitRef >= 3) fail = true;
-    } else {
-        enterExitRef = 0;
-        fail = true;
-    }
-
-    if (fail && v3Global.opt.pedantic()) {
-        v3error("`line was not properly formed with '`line number \"filename\" level'\n");
-    }
-
-    // printf ("PPLINE %d '%s'\n", s_lineno, s_filename.c_str());
+    // Fail
+    // TODO: show correct place of the code
+    v3error("`line was not properly formed with '`line number \"filename\" level'\n");
+    enterExitRef = 0;
 }
 
 void FileLine::forwardToken(const char* textp, size_t size, bool trackLines) {
@@ -293,12 +292,7 @@ FileLine* FileLine::copyOrSameFileLine() {
 
 string FileLine::filebasename() const VL_MT_SAFE { return V3Os::filenameNonDir(filename()); }
 
-string FileLine::filebasenameNoExt() const {
-    string name = filebasename();
-    string::size_type pos;
-    if ((pos = name.find('.')) != string::npos) name = name.substr(0, pos);
-    return name;
-}
+string FileLine::filebasenameNoExt() const { return V3Os::filenameNonDirExt(filename()); }
 
 string FileLine::firstColumnLetters() const VL_MT_SAFE {
     const char a = ((firstColumn() / 26) % 26) + 'a';
diff --git a/src/V3Options.cpp b/src/V3Options.cpp
index 42e33a040..9b816f63d 100644
--- a/src/V3Options.cpp
+++ b/src/V3Options.cpp
@@ -81,19 +81,21 @@ public:
 
     // ACCESSOR METHODS
     void addIncDirUser(const string& incdir) {
-        const auto itFoundPair = m_incDirUserSet.insert(incdir);
+        const string& dir = V3Os::filenameCleanup(incdir);
+        const auto itFoundPair = m_incDirUserSet.insert(dir);
         if (itFoundPair.second) {
             // cppcheck-suppress stlFindInsert  // cppcheck 1.90 bug
-            m_incDirUsers.push_back(incdir);
-            m_incDirFallbacks.remove(incdir);  // User has priority over Fallback
-            m_incDirFallbackSet.erase(incdir);  // User has priority over Fallback
+            m_incDirUsers.push_back(dir);
+            m_incDirFallbacks.remove(dir);  // User has priority over Fallback
+            m_incDirFallbackSet.erase(dir);  // User has priority over Fallback
         }
     }
     void addIncDirFallback(const string& incdir) {
-        if (m_incDirUserSet.find(incdir)
+        const string& dir = V3Os::filenameCleanup(incdir);
+        if (m_incDirUserSet.find(dir)
             == m_incDirUserSet.end()) {  // User has priority over Fallback
-            const auto itFoundPair = m_incDirFallbackSet.insert(incdir);
-            if (itFoundPair.second) m_incDirFallbacks.push_back(incdir);
+            const auto itFoundPair = m_incDirFallbackSet.insert(dir);
+            if (itFoundPair.second) m_incDirFallbacks.push_back(dir);
         }
     }
     void addLangExt(const string& langext, const V3LangCode& lc) {
@@ -508,20 +510,16 @@ string V3Options::fileExists(const string& filename) {
         return "";  // Not found
     }
     // Check if it is a directory, ignore if so
-    string filenameOut = V3Os::filenameFromDirBase(dir, basename);
+    string filenameOut = V3Os::filenameJoin(dir, basename);
     if (!fileStatNormal(filenameOut)) return "";  // Directory
     return filenameOut;
 }
 
 string V3Options::filePathCheckOneDir(const string& modname, const string& dirname) {
     for (const string& i : m_impp->m_libExtVs) {
-        const string fn = V3Os::filenameFromDirBase(dirname, modname + i);
+        const string fn = V3Os::filenameJoin(dirname, modname + i);
         string exists = fileExists(fn);
-        if (exists != "") {
-            // Strip ./, it just looks ugly
-            if (exists.substr(0, 2) == "./") exists.erase(0, 2);
-            return exists;
-        }
+        if (exists != "") return exists;
     }
     return "";
 }
@@ -548,29 +546,30 @@ string V3Options::filePath(FileLine* fl, const string& modname, const string& la
     // Find a filename to read the specified module name,
     // using the incdir and libext's.
     // Return "" if not found.
-    if (!V3Os::filenameIsRel(modname)) {
-        // modname is an absolute path, so can find getStdPackagePath()
-        string exists = filePathCheckOneDir(modname, "");
+    const string filename = V3Os::filenameCleanup(modname);
+    if (!V3Os::filenameIsRel(filename)) {
+        // filename is an absolute path, so can find getStdPackagePath()
+        string exists = filePathCheckOneDir(filename, "");
         if (exists != "") return exists;
     }
     for (const string& dir : m_impp->m_incDirUsers) {
-        string exists = filePathCheckOneDir(modname, dir);
+        string exists = filePathCheckOneDir(filename, dir);
         if (exists != "") return exists;
     }
     for (const string& dir : m_impp->m_incDirFallbacks) {
-        string exists = filePathCheckOneDir(modname, dir);
+        string exists = filePathCheckOneDir(filename, dir);
         if (exists != "") return exists;
     }
 
     if (m_relativeIncludes) {
-        const string exists = filePathCheckOneDir(modname, lastpath);
+        const string exists = filePathCheckOneDir(filename, lastpath);
         if (exists != "") return V3Os::filenameRealPath(exists);
     }
 
     // Warn and return not found
     if (errmsg != "") {
-        fl->v3error(errmsg + modname);
-        filePathLookedMsg(fl, modname);
+        fl->v3error(errmsg + filename);
+        filePathLookedMsg(fl, filename);
     }
     return "";
 }
@@ -592,13 +591,13 @@ void V3Options::filePathLookedMsg(FileLine* fl, const string& modname) {
         std::cerr << V3Error::warnMoreStandalone() << "... Looked in:" << endl;
         for (const string& dir : m_impp->m_incDirUsers) {
             for (const string& ext : m_impp->m_libExtVs) {
-                const string fn = V3Os::filenameFromDirBase(dir, modname + ext);
+                const string fn = V3Os::filenameJoin(dir, modname + ext);
                 std::cerr << V3Error::warnMoreStandalone() << "     " << fn << endl;
             }
         }
         for (const string& dir : m_impp->m_incDirFallbacks) {
             for (const string& ext : m_impp->m_libExtVs) {
-                const string fn = V3Os::filenameFromDirBase(dir, modname + ext);
+                const string fn = V3Os::filenameJoin(dir, modname + ext);
                 std::cerr << V3Error::warnMoreStandalone() << "     " << fn << endl;
             }
         }
@@ -657,7 +656,7 @@ string V3Options::getenvMAKEFLAGS() {  //
 }
 
 string V3Options::getenvPERL() {  //
-    return V3Os::getenvStr("PERL", "perl");
+    return V3Os::filenameCleanup(V3Os::getenvStr("PERL", "perl"));
 }
 
 string V3Options::getenvSYSTEMC() {
@@ -669,7 +668,7 @@ string V3Options::getenvSYSTEMC() {
         var = defenv;
         V3Os::setenvStr("SYSTEMC", var, "Hardcoded at build time");
     }
-    return var;
+    return V3Os::filenameCleanup(var);
 }
 
 string V3Options::getenvSYSTEMC_ARCH() {
@@ -718,9 +717,9 @@ string V3Options::getenvSYSTEMC_INCLUDE() {
     }
     if (var == "") {
         const string sc = getenvSYSTEMC();
-        if (sc != "") var = sc + "/include";
+        if (sc != "") var = V3Os::filenameJoin(sc, "include");
     }
-    return var;
+    return V3Os::filenameCleanup(var);
 }
 
 string V3Options::getenvSYSTEMC_LIBDIR() {
@@ -735,9 +734,9 @@ string V3Options::getenvSYSTEMC_LIBDIR() {
     if (var == "") {
         const string sc = getenvSYSTEMC();
         const string arch = getenvSYSTEMC_ARCH();
-        if (sc != "" && arch != "") var = sc + "/lib-" + arch;
+        if (sc != "" && arch != "") var = V3Os::filenameJoin(sc, "lib-" + arch);
     }
-    return var;
+    return V3Os::filenameCleanup(var);
 }
 
 string V3Options::getenvVERILATOR_ROOT() {
@@ -750,11 +749,11 @@ string V3Options::getenvVERILATOR_ROOT() {
         V3Os::setenvStr("VERILATOR_ROOT", var, "Hardcoded at build time");
     }
     if (var == "") v3fatal("$VERILATOR_ROOT needs to be in environment\n");
-    return var;
+    return V3Os::filenameCleanup(var);
 }
 
 string V3Options::getStdPackagePath() {
-    return getenvVERILATOR_ROOT() + "/include/verilated_std.sv";
+    return V3Os::filenameJoin(getenvVERILATOR_ROOT(), "include", "verilated_std.sv");
 }
 
 string V3Options::getSupported(const string& var) {
@@ -1890,7 +1889,8 @@ void V3Options::parseOptsFile(FileLine* fl, const string& filename, bool rel) VL
 
 string V3Options::parseFileArg(const string& optdir, const string& relfilename) {
     string filename = V3Os::filenameSubstitute(relfilename);
-    if (optdir != "." && V3Os::filenameIsRel(filename)) filename = optdir + "/" + filename;
+    if (optdir != "." && V3Os::filenameIsRel(filename))
+        filename = V3Os::filenameJoin(optdir, filename);
     return filename;
 }
 
diff --git a/src/V3Os.cpp b/src/V3Os.cpp
index 01d9db383..8763725c1 100644
--- a/src/V3Os.cpp
+++ b/src/V3Os.cpp
@@ -124,15 +124,46 @@ void V3Os::setenvStr(const string& envvar, const string& value, const string& wh
 //######################################################################
 // Generic filename utilities
 
-static bool isSlash(char ch) VL_PURE { return ch == '/' || ch == '\\'; }
+#if defined(_WIN32) || defined(__MINGW32__)
+static constexpr char V3OS_SLASH = '\\';
+#else
+static constexpr char V3OS_SLASH = '/';
+#endif
 
-string V3Os::filenameFromDirBase(const string& dir, const string& basename) VL_PURE {
-    // Don't return ./{filename} because if filename was absolute, that makes it relative
-    if (dir.empty() || dir == ".") {
-        return basename;
-    } else {
-        return dir + "/" + basename;
+static bool isSlash(char ch) VL_PURE {
+#if defined(_WIN32) || defined(__MINGW32__)
+    return ch == '/' || ch == '\\';
+#else
+    return ch == '/';
+#endif
+}
+
+string V3Os::filenameCleanup(const string& filename) VL_PURE {
+    string str;
+    str.reserve(filename.length());
+    bool lastIsSlash = false;
+    for (const char ch : filename) {
+        const bool lastIsSlashOld = lastIsSlash;
+        lastIsSlash = isSlash(ch);
+        if (lastIsSlash && lastIsSlashOld) continue;
+        str += ch;
     }
+    if (str.size() > 1 && isSlash(str.back())) str.pop_back();
+    while (str.size() > 2 && str[0] == '.' && isSlash(str[1])) str.erase(0, 2);
+    return str;
+}
+
+string V3Os::filenameJoin(std::initializer_list<const std::string> paths) VL_PURE {
+    string fullpath;
+    for (const auto& item : paths) {
+        if (item.empty() || item == ".") {
+            continue;
+        } else {
+            if (!fullpath.empty()) fullpath += V3OS_SLASH;
+            fullpath += item;
+        }
+    }
+    return fullpath;
 }
 
 string V3Os::filenameDir(const string& filename) VL_PURE {
@@ -144,7 +175,7 @@ string V3Os::filenameDir(const string& filename) VL_PURE {
     if (it.base() == filename.begin()) {
         return ".";
     } else {
-        return {filename.begin(), (++it).base()};
+        return string{filename.begin(), (++it).base()};
     }
 }
 
@@ -164,6 +195,10 @@ string V3Os::filenameNonExt(const string& filename) VL_PURE {
     return base;
 }
 
+string V3Os::filenameNonDirExt(const string& filename) VL_PURE {
+    return filenameNonExt(filenameNonDir(filename));
+}
+
 string V3Os::filenameSubstitute(const string& filename) {
     string result;
     // cppcheck-has-bug-suppress unusedLabel
@@ -392,3 +427,27 @@ int V3Os::system(const string& command) {
         return exit_code;
     }
 }
+
+void V3Os::selfTest() {
+#ifdef VL_DEBUG
+    UASSERT_SELFTEST(string, filenameCleanup(""), "");
+    UASSERT_SELFTEST(string, filenameCleanup("."), ".");
+    UASSERT_SELFTEST(string, filenameCleanup(".."), "..");
+    UASSERT_SELFTEST(string, filenameCleanup("/"), "/");
+    UASSERT_SELFTEST(string, filenameCleanup("../"), "..");
+    UASSERT_SELFTEST(string, filenameCleanup("//"), "/");
+    UASSERT_SELFTEST(string, filenameCleanup("//."), "/.");
+    UASSERT_SELFTEST(string, filenameCleanup("./"), ".");
+    UASSERT_SELFTEST(string, filenameCleanup("././"), ".");
+    UASSERT_SELFTEST(string, filenameCleanup(".///"), ".");
+    UASSERT_SELFTEST(string, filenameCleanup("a"), "a");
+    UASSERT_SELFTEST(string, filenameCleanup("a/"), "a");
+    UASSERT_SELFTEST(string, filenameCleanup("a/b"), "a/b");
+    UASSERT_SELFTEST(string, filenameCleanup("././//./a/b"), "a/b");
+    UASSERT_SELFTEST(string, filenameCleanup(".//./a///"), "a");
+    UASSERT_SELFTEST(string, filenameCleanup("///a/./b///."), "/a/./b/.");
+    UASSERT_SELFTEST(string, filenameCleanup("aaa/bbb/ccc/"), "aaa/bbb/ccc");
+    UASSERT_SELFTEST(string, filenameCleanup("./aaa/bbb/ccc/"), "aaa/bbb/ccc");
+    UASSERT_SELFTEST(string, filenameCleanup("../aaa/bbb/ccc/"), "../aaa/bbb/ccc");
+#endif
+}
diff --git a/src/V3Os.h b/src/V3Os.h
index da1bcb1d0..3bf69ca17 100644
--- a/src/V3Os.h
+++ b/src/V3Os.h
@@ -35,22 +35,28 @@ public:
     static void setenvStr(const string& envvar, const string& value, const string& why);
 
     // METHODS (generic filename utilities)
-    static string filenameFromDirBase(const string& dir, const string& basename) VL_PURE;
-    ///< Return non-directory part of filename
+    ///< @return concatenated path
+    static string filenameJoin(std::initializer_list<const std::string> paths) VL_PURE;
+    template <typename... Args>
+    static string filenameJoin(Args... args) VL_PURE {
+        return filenameJoin({args...});
+    };
+    ///< @return file path without repeated separators and ./ prefix
+    static string filenameCleanup(const string& filename) VL_PURE;
+    ///< @return non-directory part of filename
     static string filenameNonDir(const string& filename) VL_PURE;
-    ///< Return non-extensioned (no .) part of filename
+    ///< @return non-extensioned (no .) part of filename
     static string filenameNonExt(const string& filename) VL_PURE;
-    ///< Return basename of filename
-    static string filenameNonDirExt(const string& filename) VL_PURE {
-        return filenameNonExt(filenameNonDir(filename));
-    }
-    ///< Return directory part of filename
+    ///< @return basename of filename
+    static string filenameNonDirExt(const string& filename) VL_PURE;
+    ///< @return directory part of filename
     static string filenameDir(const string& filename) VL_PURE;
-    /// Return filename with env vars removed
+    ///< @return filename with env vars removed
     static string filenameSubstitute(const string& filename);
-    ///< Return realpath of filename
+    ///< @return realpath of filename
     static string filenameRealPath(const string& filename) VL_PURE;
-    static bool filenameIsRel(const string& filename) VL_PURE;  ///< True if relative
+    ///< @return filename is relative
+    static bool filenameIsRel(const string& filename) VL_PURE;
 
     // METHODS (file utilities)
     static string getline(std::istream& is, char delim = '\n');
@@ -72,6 +78,7 @@ public:
     // METHODS (sub command)
     /// Run system command, returns the exit code of the child process.
     static int system(const string& command);
+    static void selfTest();
 };
 
 #endif  // Guard
diff --git a/src/V3ParseGrammar.cpp b/src/V3ParseGrammar.cpp
index 10be43782..384ec1ffa 100644
--- a/src/V3ParseGrammar.cpp
+++ b/src/V3ParseGrammar.cpp
@@ -251,63 +251,9 @@ AstVar* V3ParseGrammar::createVariable(FileLine* fileline, const string& name,
     return nodep;
 }
 
-string V3ParseGrammar::deQuote(FileLine* fileline, string text) {
-    // Fix up the quoted strings the user put in, for example "\"" becomes "
-    // Reverse is V3OutFormatter::quoteNameControls(...)
-    bool quoted = false;
-    string newtext;
-    unsigned char octal_val = 0;
-    int octal_digits = 0;
-    for (string::const_iterator cp = text.begin(); cp != text.end(); ++cp) {
-        if (quoted) {
-            if (std::isdigit(*cp)) {
-                octal_val = octal_val * 8 + (*cp - '0');
-                if (++octal_digits == 3) {
-                    octal_digits = 0;
-                    quoted = false;
-                    newtext += octal_val;
-                }
-            } else {
-                if (octal_digits) {
-                    // Spec allows 1-3 digits
-                    octal_digits = 0;
-                    quoted = false;
-                    newtext += octal_val;
-                    --cp;  // Backup to reprocess terminating character as non-escaped
-                    continue;
-                }
-                quoted = false;
-                if (*cp == 'n') {
-                    newtext += '\n';
-                } else if (*cp == 'a') {
-                    newtext += '\a';  // SystemVerilog 3.1
-                } else if (*cp == 'f') {
-                    newtext += '\f';  // SystemVerilog 3.1
-                } else if (*cp == 'r') {
-                    newtext += '\r';
-                } else if (*cp == 't') {
-                    newtext += '\t';
-                } else if (*cp == 'v') {
-                    newtext += '\v';  // SystemVerilog 3.1
-                } else if (*cp == 'x' && std::isxdigit(cp[1])
-                           && std::isxdigit(cp[2])) {  // SystemVerilog 3.1
-#define vl_decodexdigit(c) ((std::isdigit(c) ? ((c) - '0') : (std::tolower((c)) - 'a' + 10)))
-                    newtext
-                        += static_cast<char>(16 * vl_decodexdigit(cp[1]) + vl_decodexdigit(cp[2]));
-                    cp += 2;
-                } else if (std::isalnum(*cp)) {
-                    fileline->v3error("Unknown escape sequence: \\" << *cp);
-                    break;
-                } else {
-                    newtext += *cp;
-                }
-            }
-        } else if (*cp == '\\') {
-            quoted = true;
-            octal_digits = 0;
-        } else {
-            newtext += *cp;
-        }
-    }
-    return newtext;
+string V3ParseGrammar::unquoteString(FileLine* fileline, string text) {
+    string errMsg;
+    string res = VString::unquoteSVString(text, errMsg);
+    if (!errMsg.empty()) fileline->v3error(errMsg.c_str());
+    return res;
 }
diff --git a/src/V3PreProc.cpp b/src/V3PreProc.cpp
index 075d677d2..7769dd41a 100644
--- a/src/V3PreProc.cpp
+++ b/src/V3PreProc.cpp
@@ -358,7 +358,7 @@ string V3PreProcImp::removeDefines(const string& text) {
     string rtnsym = text;
     for (int loopprevent = 0; loopprevent < 100; loopprevent++) {
         string xsym = rtnsym;
-        if (xsym.substr(0, 1) == "`") xsym.replace(0, 1, "");
+        if (xsym[0] == '`') xsym.erase(0, 1);
         if (defExists(xsym)) {
             val = defValue(xsym);
             if (val != rtnsym) {
diff --git a/src/V3Sched.cpp b/src/V3Sched.cpp
index 32386e38b..b3849955d 100644
--- a/src/V3Sched.cpp
+++ b/src/V3Sched.cpp
@@ -663,7 +663,8 @@ std::pair<AstVarScope*, AstNodeStmt*> makeEvalLoop(AstNetlist* netlistp, const s
                 newcallp->dtypeSetVoid();
                 blockp->addNodesp(newcallp->makeStmt());
                 add("#endif\n");
-                add("VL_FATAL_MT(\"" + file + "\", " + line + ", \"\", ");
+                add("VL_FATAL_MT(\"" + V3OutFormatter::quoteNameControls(file) + "\", " + line
+                    + ", \"\", ");
                 add("\"" + name + " region did not converge.\");\n");
             }
 
diff --git a/src/V3String.cpp b/src/V3String.cpp
index 5ed5279e1..c23a15705 100644
--- a/src/V3String.cpp
+++ b/src/V3String.cpp
@@ -20,6 +20,7 @@
 #include "V3String.h"
 
 #include "V3Error.h"
+#include "V3FileLine.h"
 
 #ifndef V3ERROR_NO_GLOBAL_
 #include "V3Global.h"
@@ -130,6 +131,70 @@ string VString::escapeStringForPath(const string& str) {
     return result;
 }
 
+static int vl_decodexdigit(char c) {
+    return std::isdigit(c) ? c - '0' : std::tolower(c) - 'a' + 10;
+}
+
+string VString::unquoteSVString(const string& text, string& errOut) {
+    bool quoted = false;
+    string newtext;
+    newtext.reserve(text.size());
+    unsigned char octal_val = 0;
+    int octal_digits = 0;
+    for (string::const_iterator cp = text.begin(); cp != text.end(); ++cp) {
+        if (quoted) {
+            if (std::isdigit(*cp)) {
+                octal_val = octal_val * 8 + (*cp - '0');
+                if (++octal_digits == 3) {
+                    octal_digits = 0;
+                    quoted = false;
+                    newtext += octal_val;
+                }
+            } else {
+                if (octal_digits) {
+                    // Spec allows 1-3 digits
+                    octal_digits = 0;
+                    quoted = false;
+                    newtext += octal_val;
+                    --cp;  // Backup to reprocess terminating character as non-escaped
+                    continue;
+                }
+                quoted = false;
+                if (*cp == 'n') {
+                    newtext += '\n';
+                } else if (*cp == 'a') {
+                    newtext += '\a';  // SystemVerilog 3.1
+                } else if (*cp == 'f') {
+                    newtext += '\f';  // SystemVerilog 3.1
+                } else if (*cp == 'r') {
+                    newtext += '\r';
+                } else if (*cp == 't') {
+                    newtext += '\t';
+                } else if (*cp == 'v') {
+                    newtext += '\v';  // SystemVerilog 3.1
+                } else if (*cp == 'x' && std::isxdigit(cp[1])
+                           && std::isxdigit(cp[2])) {  // SystemVerilog 3.1
+                    newtext
+                        += static_cast<char>(16 * vl_decodexdigit(cp[1]) + vl_decodexdigit(cp[2]));
+                    cp += 2;
+                } else if (std::isalnum(*cp)) {
+                    errOut = "Unknown escape sequence: \\";
+                    errOut += *cp;
+                    break;
+                } else {
+                    newtext += *cp;
+                }
+            }
+        } else if (*cp == '\\') {
+            quoted = true;
+            octal_digits = 0;
+        } else {
+            newtext += *cp;
+        }
+    }
+    return newtext;
+}
+
 string VString::spaceUnprintable(const string& str) VL_PURE {
     string result;
     for (const char c : str) {
diff --git a/src/V3String.h b/src/V3String.h
index cbca5de56..33c792757 100644
--- a/src/V3String.h
+++ b/src/V3String.h
@@ -102,6 +102,9 @@ public:
     // Surround a raw string by double quote and escape if necessary
     // e.g. input abc's  becomes "\"abc\'s\""
     static string escapeStringForPath(const string& str);
+    // Convert SV quoted string input from source code to normal form.
+    // Reverse is V3OutFormatter::quoteNameControls(...)
+    static string unquoteSVString(const string& text, string& errOut);
     // Escape path in Windows
     // e.g. input `C:\Program Files\My Program\My Program.exe` becomes
     // `C:\\Program\ Files\\My\ Program\\My\ Program.exe`
diff --git a/src/Verilator.cpp b/src/Verilator.cpp
index 10b0fb06d..cb2109ea0 100644
--- a/src/Verilator.cpp
+++ b/src/Verilator.cpp
@@ -642,6 +642,7 @@ static void verilate(const string& argString) {
         {
             const V3MtDisabledLockGuard mtDisabler{v3MtDisabledLock()};
 
+            V3Os::selfTest();
             VHashSha256::selfTest();
             VSpellCheck::selfTest();
             V3Graph::selfTest();
@@ -782,7 +783,7 @@ int main(int argc, char** argv) {
         V3PreShell::boot();
 
         // Command option parsing
-        v3Global.opt.buildDepBin(VString::escapeStringForPath(argv[0]));
+        v3Global.opt.buildDepBin(V3Os::filenameCleanup(argv[0]));
         v3Global.opt.parseOpts(new FileLine{FileLine::commandLineFilename()}, argc - 1, argv + 1);
 
         // Validate settings (aka Boost.Program_options)
diff --git a/src/verilog.y b/src/verilog.y
index 2b9120969..39f2e31ff 100644
--- a/src/verilog.y
+++ b/src/verilog.y
@@ -129,7 +129,7 @@ public:
                            AstNode* attrsp) VL_MT_DISABLED;
     AstNode* createSupplyExpr(FileLine* fileline, const string& name, int value) VL_MT_DISABLED;
     AstText* createTextQuoted(FileLine* fileline, const string& text) {
-        string newtext = deQuote(fileline, text);
+        string newtext = GRAMMARP->unquoteString(fileline, text);
         return new AstText{fileline, newtext};
     }
     AstNode* createCellOrIfaceRef(FileLine* fileline, const string& name, AstPin* pinlistp,
@@ -253,7 +253,7 @@ public:
             return createArray(dtypep, rangearraysp, isPacked);
         }
     }
-    string deQuote(FileLine* fileline, string text) VL_MT_DISABLED;
+    string unquoteString(FileLine* fileline, string text) VL_MT_DISABLED;
     void checkDpiVer(FileLine* fileline, const string& str) {
         if (str != "DPI-C" && !v3Global.opt.bboxSys()) {
             fileline->v3error("Unsupported DPI type '" << str << "': Use 'DPI-C'");
@@ -5675,13 +5675,13 @@ parseRefBase<nodep>:
 
 // yaSTRING shouldn't be used directly, instead via an abstraction below
 str<strp>:                      // yaSTRING but with \{escapes} need decoded
-                yaSTRING                                { $$ = PARSEP->newString(GRAMMARP->deQuote($<fl>1, *$1)); }
+                yaSTRING                                { $$ = PARSEP->newString(GRAMMARP->unquoteString($<fl>1, *$1)); }
         ;
 
 strAsInt<nodeExprp>:
                 yaSTRING
                         { // Numeric context, so IEEE 1800-2017 11.10.3 "" is a "\000"
-                          $$ = new AstConst{$<fl>1, AstConst::VerilogStringLiteral{}, GRAMMARP->deQuote($<fl>1, *$1)}; }
+                          $$ = new AstConst{$<fl>1, AstConst::VerilogStringLiteral{}, GRAMMARP->unquoteString($<fl>1, *$1)}; }
         ;
 
 strAsIntIgnore<nodeExprp>:          // strAsInt, but never matches for when expr shouldn't parse strings
diff --git a/test_regress/t/t_pp_line.out b/test_regress/t/t_pp_line.out
new file mode 100644
index 000000000..a3e32422f
--- /dev/null
+++ b/test_regress/t/t_pp_line.out
@@ -0,0 +1,16 @@
+-Info: some file:100:1: aaaaaaaa
+                      : ... note: In instance 't'
+  100 | $info("aaaaaaaa");
+      | ^~~~~
+-Info: some file:101:1: bbbbbbbb
+                      : ... note: In instance 't'
+  101 | $info("bbbbbbbb");
+      | ^~~~~
+-Info: somefile.v:200:1: cccccccc
+                       : ... note: In instance 't'
+  200 | $info("cccccccc");
+      | ^~~~~
+-Info: /a/somefile.v:300:1: dddddddd
+                          : ... note: In instance 't'
+  300 | $info("dddddddd");
+      | ^~~~~
diff --git a/test_regress/t/t_pp_line.pl b/test_regress/t/t_pp_line.pl
new file mode 100755
index 000000000..d1ed9a923
--- /dev/null
+++ b/test_regress/t/t_pp_line.pl
@@ -0,0 +1,18 @@
+#!/usr/bin/env perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+scenarios(linter => 1);
+
+lint(
+    expect_filename => $Self->{golden_filename},
+    );
+
+ok(1);
+1;
diff --git a/test_regress/t/t_pp_line.v b/test_regress/t/t_pp_line.v
new file mode 100644
index 000000000..ac991e550
--- /dev/null
+++ b/test_regress/t/t_pp_line.v
@@ -0,0 +1,15 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2023 by Anthony Donlon.
+// SPDX-License-Identifier: CC0-1.0
+
+module t;
+`line 100 "some file" 0
+$info("aaaaaaaa");
+$info("bbbbbbbb");
+`line 200 "somefile.v" 0
+$info("cccccccc");
+`line 300 "/a/somefile.v" 0
+$info("dddddddd");
+endmodule
diff --git a/test_regress/t/t_pp_line_bad.out b/test_regress/t/t_pp_line_bad.out
index 062cbf6af..8365b61c6 100644
--- a/test_regress/t/t_pp_line_bad.out
+++ b/test_regress/t/t_pp_line_bad.out
@@ -1,13 +1,22 @@
 %Error: t/t_pp_line_bad.v:100:1: `line was not properly formed with '`line number "filename" level'
   100 | `line 100
       | ^
-%Error: somefile:100:1: `line was not properly formed with '`line number "filename" level'
-  100 | `line 100
+%Error: t/t_pp_line_bad.v:200:1: `line was not properly formed with '`line number "filename" level'
+  200 | `line 100
+      | ^
+%Error: t/t_pp_line_bad.v:300:1: `line was not properly formed with '`line number "filename" level'
+  300 | `line 100
+      | ^
+%Error: some file:400:1: `line was not properly formed with '`line number "filename" level'
+  400 | `line 100
+      | ^
+%Error: somefile:500:1: `line was not properly formed with '`line number "filename" level'
+  500 | `line 100
+      | ^
+%Error: some file:600:1: `line was not properly formed with '`line number "filename" level'
+  600 | `line 100
       | ^
-%Error: somefile:100:1: `line was not properly formed with '`line number "filename" level'
 %Error: t/t_pp_line_bad.v:7:1: Define or directive not defined: '`line'
     7 | `line
       | ^~~~~
-%Error: somefile:100:1: `line was not properly formed with '`line number "filename" level'
-        t/t_pp_line_bad.v:101:1: ... note: In file included from 't_pp_line_bad.v'
 %Error: Exiting due to
diff --git a/test_regress/t/t_pp_line_bad.pl b/test_regress/t/t_pp_line_bad.pl
index 9de6b85ee..a60503a1f 100755
--- a/test_regress/t/t_pp_line_bad.pl
+++ b/test_regress/t/t_pp_line_bad.pl
@@ -8,10 +8,9 @@ if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); di
 # Version 2.0.
 # SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
 
-scenarios(vlt => 1);
+scenarios(linter => 1);
 
 lint(
-    verilator_flags2 => ["-Wpedantic"],
     fails => 1,
     expect_filename => $Self->{golden_filename},
     );
diff --git a/test_regress/t/t_pp_line_bad.v b/test_regress/t/t_pp_line_bad.v
index e1ac808a4..0d41247a1 100644
--- a/test_regress/t/t_pp_line_bad.v
+++ b/test_regress/t/t_pp_line_bad.v
@@ -6,6 +6,8 @@
 
 `line
 `line 100
-`line 100 somefile 1
-`line 100 "somefile"
-`line 100 "somefile" 3
+`line 200 somefile
+`line 300 "somefile 1
+`line 400 "some file"
+`line 500 "somefile" 3
+`line 600 "some file" 3