Support named filehandles in filehandle duplication

src/main/java/org/perlonjava/operators/IOOperator.java

@@ -1852,21 +1852,44 @@ private static RuntimeIO findFileHandleByDescriptor(int fd) {
     public static RuntimeIO openFileHandleDup(String fileName, String mode) {
         boolean isParsimonious = mode.endsWith("="); // &= modes reuse file descriptor
 
+        RuntimeIO sourceHandle = null;
+
         // Check if it's a numeric file descriptor
         if (fileName.matches("^\\d+$")) {
             int fd = Integer.parseInt(fileName);
-            RuntimeIO sourceHandle = findFileHandleByDescriptor(fd);
-            if (sourceHandle != null && sourceHandle.ioHandle != null) {
-                if (isParsimonious) {
-                    return sourceHandle;
-                } else {
-                    return duplicateFileHandle(sourceHandle);
-                }
-            } else {
+            sourceHandle = findFileHandleByDescriptor(fd);
+            if (sourceHandle == null || sourceHandle.ioHandle == null) {
                 throw new PerlCompilerException("Bad file descriptor: " + fd);
             }
         } else {
-            throw new PerlCompilerException("Unsupported filehandle duplication: " + fileName);
+            // Handle named filehandles like STDERR, STDOUT, STDIN
+            switch (fileName.toUpperCase()) {
+                case "STDIN":
+                    sourceHandle = RuntimeIO.stdin;
+                    break;
+                case "STDOUT":
+                    sourceHandle = RuntimeIO.stdout;
+                    break;
+                case "STDERR":
+                    sourceHandle = RuntimeIO.stderr;
+                    break;
+                default:
+                    // Try to look up as a global filehandle
+                    String normalizedName = fileName.contains("::") ? fileName : "main::" + fileName;
+                    RuntimeGlob glob = GlobalVariable.getGlobalIO(normalizedName);
+                    if (glob != null) {
+                        sourceHandle = glob.getRuntimeIO();
+                    }
+                    if (sourceHandle == null || sourceHandle.ioHandle == null) {
+                        throw new PerlCompilerException("Unsupported filehandle duplication: " + fileName);
+                    }
+            }
+        }
+
+        if (isParsimonious) {
+            return sourceHandle;
+        } else {
+            return duplicateFileHandle(sourceHandle);
         }
     }
 

src/test/resources/unit/filehandle_dup.t

@@ -0,0 +1,69 @@
+use strict;
+use warnings;
+use Test::More tests => 4;
+
+# Test filehandle duplication with named filehandles (STDERR, STDOUT, STDIN)
+# This is a regression test for the "Unsupported filehandle duplication: STDERR" error
+
+subtest 'duplicate STDERR by name' => sub {
+    plan tests => 2;
+
+    # Save STDERR to a new filehandle
+    open my $saveerr, ">&STDERR" or die "Cannot dup STDERR: $!";
+    ok(defined $saveerr, 'Duplicated STDERR to lexical filehandle');
+
+    # Write to the duplicated handle
+    print $saveerr "";  # Just test that we can write without error
+    ok(1, 'Can write to duplicated STDERR handle');
+
+    close $saveerr;
+};
+
+subtest 'duplicate STDOUT by name' => sub {
+    plan tests => 2;
+
+    # Save STDOUT to a new filehandle
+    open my $saveout, ">&STDOUT" or die "Cannot dup STDOUT: $!";
+    ok(defined $saveout, 'Duplicated STDOUT to lexical filehandle');
+
+    # Write to the duplicated handle
+    print $saveout "";  # Just test that we can write without error
+    ok(1, 'Can write to duplicated STDOUT handle');
+
+    close $saveout;
+};
+
+subtest 'duplicate by file descriptor number' => sub {
+    plan tests => 2;
+
+    # Duplicate STDERR using file descriptor 2
+    open my $saveerr, ">&2" or die "Cannot dup fd 2: $!";
+    ok(defined $saveerr, 'Duplicated fd 2 (STDERR) to lexical filehandle');
+
+    # Duplicate STDOUT using file descriptor 1
+    open my $saveout, ">&1" or die "Cannot dup fd 1: $!";
+    ok(defined $saveout, 'Duplicated fd 1 (STDOUT) to lexical filehandle');
+
+    close $saveerr;
+    close $saveout;
+};
+
+subtest 'redirect and restore STDERR' => sub {
+    plan tests => 2;
+
+    # This pattern is commonly used to temporarily suppress STDERR
+    my $dummy = \*SAVEERR;  # avoid "used only once" warning
+
+    # Save STDERR
+    open SAVEERR, ">&STDERR" or die "Cannot save STDERR: $!";
+    ok(1, 'Saved STDERR to bareword filehandle');
+
+    # Restore STDERR
+    close STDERR;
+    open STDERR, ">&SAVEERR" or die "Cannot restore STDERR: $!";
+    ok(1, 'Restored STDERR from saved handle');
+
+    close SAVEERR;
+};
+
+1;