diff --git a/applications/test/fileOperation1/Make/files b/applications/test/fileOperation1/Make/files
index 3f4a231f16..8f7d27ee23 100644
--- a/applications/test/fileOperation1/Make/files
+++ b/applications/test/fileOperation1/Make/files
@@ -1,3 +1,3 @@
-Test-fileOperation1.C
+Test-fileOperation1.cxx
 
 EXE = $(FOAM_USER_APPBIN)/Test-fileOperation1
diff --git a/applications/test/fileOperation1/Test-fileOperation1.C b/applications/test/fileOperation1/Test-fileOperation1.cxx
similarity index 96%
rename from applications/test/fileOperation1/Test-fileOperation1.C
rename to applications/test/fileOperation1/Test-fileOperation1.cxx
index e395ea292d..78f3d24e5e 100644
--- a/applications/test/fileOperation1/Test-fileOperation1.C
+++ b/applications/test/fileOperation1/Test-fileOperation1.cxx
@@ -27,7 +27,7 @@ Application
     Test-fileOperation1
 
 Description
-   Test string parsing and other bits for fileOperation
+    Test string parsing and other bits for fileOperation
 
 \*---------------------------------------------------------------------------*/
 
@@ -42,7 +42,8 @@ Description
 
 using namespace Foam;
 
-word toString(const fileOperation::procRangeType& group)
+template<class IntType>
+word toString(const IntRange<IntType>& group)
 {
     if (group.empty())
     {
diff --git a/applications/utilities/parallelProcessing/redistributePar/loadOrCreateMesh.C b/applications/utilities/parallelProcessing/redistributePar/loadOrCreateMesh.C
index 3e94d450da..5a6359add1 100644
--- a/applications/utilities/parallelProcessing/redistributePar/loadOrCreateMesh.C
+++ b/applications/utilities/parallelProcessing/redistributePar/loadOrCreateMesh.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2012-2017 OpenFOAM Foundation
-    Copyright (C) 2015-2024 OpenCFD Ltd.
+    Copyright (C) 2015-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -78,11 +78,9 @@ bool Foam::checkFileExistence(const fileName& fName)
         for (const fileName& dirN : dirEntries)
         {
             // Analyse directory name
-            fileName rp, rd, rl;
-            label rNum;
+            label rNum(-1);
             const label readProci =
-                fileOperation::splitProcessorPath
-                (dirN, rp, rd, rl, group, rNum);
+                fileOperation::detectProcessorPath(dirN, group, &rNum);
 
             if (proci == readProci)
             {
@@ -211,18 +209,8 @@ Foam::boolList Foam::haveMeshFile
             // Collect local block number
             label myBlockNumber = -1;
             {
-                fileName path, pDir, local;
                 procRangeType group;
-                label numProcs;
-                label proci = fileOperation::splitProcessorPath
-                (
-                    fName,
-                    path,
-                    pDir,
-                    local,
-                    group,
-                    numProcs
-                );
+                label proci = fileOperation::detectProcessorPath(fName, group);
 
                 if (proci == -1 && group.empty())
                 {
diff --git a/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C b/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C
index a9dda1fcb7..0b262f41f1 100644
--- a/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2017-2018 OpenFOAM Foundation
-    Copyright (C) 2020-2023 OpenCFD Ltd.
+    Copyright (C) 2020-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -154,7 +154,7 @@ bool Foam::fileOperations::collatedFileOperation::appendObject
 {
     // Append to processorsNN/ file
 
-    const label proci = detectProcessorPath(io.objectPath());
+    const label proci = fileOperation::detectProcessorPath(io.objectPath());
 
     if (debug)
     {
@@ -544,7 +544,7 @@ Foam::word Foam::fileOperations::collatedFileOperation::processorsDir
 {
     if (UPstream::parRun())
     {
-        const List<int>& procs(UPstream::procID(comm_));
+        const auto& procs = UPstream::procID(comm_);
 
         word procDir(processorsBaseDir+Foam::name(nProcs_));
 
@@ -565,7 +565,7 @@ Foam::word Foam::fileOperations::collatedFileOperation::processorsDir
         if (ioRanks_.size())
         {
             // Detect current processor number
-            label proci = detectProcessorPath(fName);
+            label proci = fileOperation::detectProcessorPath(fName);
 
             if (proci != -1)
             {
diff --git a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
index 2d7f0839d5..3ad19e15cf 100644
--- a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2017-2018 OpenFOAM Foundation
-    Copyright (C) 2019-2024 OpenCFD Ltd.
+    Copyright (C) 2019-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -524,12 +524,11 @@ Foam::fileOperation::lookupAndCacheProcessorsPath
         for (const fileName& dirN : dirEntries)
         {
             // Analyse directory name
-            fileName rp, rd, rl;
-            label rNum;
+            label rNum(-1);
             const label readProci =
-                splitProcessorPath(dirN, rp, rd, rl, group, rNum);
+                fileOperation::detectProcessorPath(dirN, group, &rNum);
 
-            nProcs = max(nProcs, readProci+1);
+            nProcs = Foam::max(nProcs, readProci+1);
 
             Tuple2<pathType, int> pathTypeIdx(pathType::NOTFOUND, 0);
 
@@ -554,7 +553,7 @@ Foam::fileOperation::lookupAndCacheProcessorsPath
                 }
 
                 // "processorsNN" or "processorsNN_start-end"
-                nProcs = max(nProcs, rNum);
+                nProcs = Foam::max(nProcs, rNum);
 
                 if (group.empty())
                 {
@@ -581,7 +580,7 @@ Foam::fileOperation::lookupAndCacheProcessorsPath
 
             if (pathTypeIdx.first() != pathType::NOTFOUND)
             {
-                procDirs.append(dirIndex(dirN, pathTypeIdx));
+                procDirs.emplace_back(dirN, pathTypeIdx);
             }
         }
 
@@ -621,7 +620,7 @@ Foam::fileOperation::lookupAndCacheProcessorsPath
                 int flavour(pathType::PROCUNCOLLATED);
                 for (const dirIndex& pDir : procDirs)
                 {
-                    flavour = max(flavour, int(pDir.second().first()));
+                    flavour = Foam::max(flavour, int(pDir.second().first()));
                 }
 
                 reduce(nProcs, maxOp<label>());  // worldComm
@@ -640,13 +639,10 @@ Foam::fileOperation::lookupAndCacheProcessorsPath
                     {
                         pathTypeIdx.second() = proci;
 
-                        procDirs.append
+                        procDirs.emplace_back
                         (
-                            dirIndex
-                            (
-                                processorsBaseDir + Foam::name(nProcs),
-                                pathTypeIdx
-                            )
+                            processorsBaseDir + Foam::name(nProcs),
+                            pathTypeIdx
                         );
                     }
                     else
@@ -655,13 +651,10 @@ Foam::fileOperation::lookupAndCacheProcessorsPath
                         // - poor fallback for pathType::PROCOBJECT
                         // - out-of-range pathType::PROCBASEOBJECT
 
-                        procDirs.append
+                        procDirs.emplace_back
                         (
-                            dirIndex
-                            (
-                                "processor" + Foam::name(proci),
-                                pathTypeIdx
-                            )
+                            "processor" + Foam::name(proci),
+                            pathTypeIdx
                         );
                     }
 
@@ -1342,12 +1335,12 @@ Foam::label Foam::fileOperation::nProcs
             const label readProci =
                 splitProcessorPath(dirN, rp, rd, rl, group, rNum);
 
-            maxProc = max(maxProc, readProci);
+            maxProc = Foam::max(maxProc, readProci);
 
             if (rNum > 0)       // processorsDDD where DDD>0
             {
                 // Use processors number
-                maxProc = max(maxProc, rNum-1);
+                maxProc = Foam::max(maxProc, rNum-1);
                 // Mark in cache. TBD separate handling for groups?
                 foundDirs.set(labelRange(0, rNum));
 
@@ -1632,12 +1625,39 @@ Foam::label Foam::fileOperation::splitProcessorPath
 }
 
 
+Foam::label Foam::fileOperation::detectProcessorPath
+(
+    const fileName& objPath,
+    procRangeType& group,
+    label* numProcs
+)
+{
+    fileName path, procDir, local;
+    label nProcs;
+
+    label proci = fileOperation::splitProcessorPath
+    (
+        objPath,
+        path,
+        procDir,
+        local,
+        group,
+        nProcs
+    );
+
+    if (numProcs)
+    {
+        *numProcs = nProcs;
+    }
+
+    return proci;
+}
+
+
 Foam::label Foam::fileOperation::detectProcessorPath(const fileName& fName)
 {
-    fileName path, pDir, local;
     procRangeType group;
-    label nProcs;
-    return splitProcessorPath(fName, path, pDir, local, group, nProcs);
+    return fileOperation::detectProcessorPath(fName, group);
 }
 
 
diff --git a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
index 0850d3d87c..f593a7c57b 100644
--- a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2017 OpenFOAM Foundation
-    Copyright (C) 2020-2024 OpenCFD Ltd.
+    Copyright (C) 2020-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -138,9 +138,8 @@ public:
         typedef Tuple2<fileName, Tuple2<pathType, int>> dirIndex;
         typedef List<dirIndex> dirIndexList;
 
-        //- For addressing a range of processors,
-        //- identical to UPstream::rangeType
-        typedef IntRange<int> procRangeType;
+        //- For addressing a range of processors (an int range)
+        typedef UPstream::rangeType procRangeType;
 
 
 private:
@@ -933,16 +932,32 @@ public:
             static label splitProcessorPath
             (
                 const fileName& objectPath,
+                //! [out] the leading part of the path
                 fileName& path,
+                //! [out] the processor directory name
                 fileName& procDir,
+                //! [out] the local path
                 fileName& local,
+                //! [out] any detected collated grouping
                 procRangeType& group,
+                //! [out] detected number of processors, -1 if none detected
                 label& nProcs
             );
 
             //- Detect processor number from '/aa/bb/processorDDD/cc'
             static label detectProcessorPath(const fileName& objPath);
 
+            //- Detect processor number from 'path/processorDDD/abc'
+            //- or 'path/processorsNN/abc', 'path/processorsNN_0-10/abc'
+            static label detectProcessorPath
+            (
+                const fileName& objPath,
+                //! [out] any detected collated grouping
+                procRangeType& group,
+                //! [out] detected number of collated processors, -1 if none
+                label* numProcs = nullptr
+            );
+
 
     // Rank selection/sub-selection
 
diff --git a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
index dd15a6eab5..623891be2a 100644
--- a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
@@ -1984,17 +1984,15 @@ Foam::fileOperations::masterUncollatedFileOperation::readStream
         // Note: this should really be part of filePath() which should return
         // both file and index in file.
 
-        fileName path, procDir, local;
         procRangeType group;
-        label nProcs;
-        splitProcessorPath(fName, path, procDir, local, group, nProcs);
+        fileOperation::detectProcessorPath(fName, group);
 
 
         if (!UPstream::parRun())
         {
             // Analyse the objectpath to find out the processor we're trying
             // to access
-            label proci = detectProcessorPath(io.objectPath());
+            label proci = fileOperation::detectProcessorPath(io.objectPath());
 
             if (proci == -1)
             {
@@ -2009,7 +2007,7 @@ Foam::fileOperations::masterUncollatedFileOperation::readStream
             // The local rank (offset)
             if (!group.empty())
             {
-                proci = proci - group.start();
+                proci -= group.start();
             }
 
             if (debug)
@@ -2053,7 +2051,7 @@ Foam::fileOperations::masterUncollatedFileOperation::readStream
             // Get size of file to determine communications type
             bool bigSize = false;
 
-            if (Pstream::master(UPstream::worldComm))
+            if (UPstream::master(UPstream::worldComm))
             {
                 // TBD: handle multiple masters?
                 bigSize =
@@ -2064,7 +2062,7 @@ Foam::fileOperations::masterUncollatedFileOperation::readStream
             }
             // Reduce (not broadcast)
             // - if we have multiple master files (FUTURE)
-            Pstream::reduceOr(bigSize, UPstream::worldComm);
+            UPstream::reduceOr(bigSize, UPstream::worldComm);
 
             const UPstream::commsTypes myCommsType
             (
@@ -2610,12 +2608,10 @@ void Foam::fileOperations::masterUncollatedFileOperation::sync()
         if (Pstream::parRun() && !Pstream::master(UPstream::worldComm))
         {
             // Replace processor0 ending with processorDDD
-            fileName path;
-            fileName pDir;
-            fileName local;
+            fileName path, pDir, local;
             procRangeType group;
             label numProcs;
-            const label proci = splitProcessorPath
+            const label proci = fileOperation::splitProcessorPath
             (
                 dir,
                 path,
diff --git a/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.C b/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.C
index 824c875d19..c4879d889c 100644
--- a/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2017 OpenFOAM Foundation
-    Copyright (C) 2020-2024 OpenCFD Ltd.
+    Copyright (C) 2020-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -661,7 +661,7 @@ Foam::fileOperations::uncollatedFileOperation::readStream
     {
         // Analyse the objectpath to find out the processor we're trying
         // to access
-        label proci = detectProcessorPath(io.objectPath());
+        label proci = fileOperation::detectProcessorPath(io.objectPath());
 
         if (proci == -1)
         {
@@ -675,15 +675,13 @@ Foam::fileOperations::uncollatedFileOperation::readStream
         // Analyse the fileName for any processor subset. Note: this
         // should really be part of filePath() which should return
         // both file and index in file.
-        fileName path, procDir, local;
         procRangeType group;
-        label nProcs;
-        splitProcessorPath(fName, path, procDir, local, group, nProcs);
+        fileOperation::detectProcessorPath(fName, group);
 
         // The local rank (offset)
         if (!group.empty())
         {
-            proci = proci - group.start();
+            proci -= group.start();
         }
 
         // Read data and return as stream