Unity-Technologies/UnityCsReference · error · IOException

Failed to Copy File / Directory from '{0}' to '{1}': destina

Error message

Failed to Copy File / Directory from '{0}' to '{1}': destination path already exists.

What it means

CopyFileOrDirectory refuses to overwrite: if the destination already exists (checked via the native PathExists), it throws System.IO.IOException with the source/dest formatted in, before invoking the native copy. This is a deliberate fail-loud policy — the native copy does not merge or replace.

Source

Thrown at Editor/Mono/FileUtil.bindings.cs:41

            if (path == string.Empty) throw new ArgumentException("path", "The path cannot be empty.");

            return DeleteFileOrDirectoryInternal(path);
        }

        [FreeFunction("DeleteFileOrDirectory")]
        private static extern bool DeleteFileOrDirectoryInternal(string path);

        [FreeFunction("IsPathCreated")]
        private static extern bool PathExists(string path);

        // Copies a file or directory.
        public static void CopyFileOrDirectory(string source, string dest)
        {
            CheckForValidSourceAndDestinationArgumentsAndRaiseAnExceptionWhenNullOrEmpty(source, dest);

            if (PathExists(dest))
            {
                throw new System.IO.IOException(string.Format(
                    "Failed to Copy File / Directory from '{0}' to '{1}': destination path already exists.", source, dest));
            }

            if (!CopyFileOrDirectoryInternal(source, dest))
            {
                throw new System.IO.IOException(string.Format(
                    "Failed to Copy File / Directory from '{0}' to '{1}'.", source, dest));
            }
        }

        [FreeFunction("CopyFileOrDirectory")]
        private static extern bool CopyFileOrDirectoryInternal(string source, string dest);

        // Copies the file or directory following symbolic links.
        public static void CopyFileOrDirectoryFollowSymlinks(string source, string dest)
        {
            CheckForValidSourceAndDestinationArgumentsAndRaiseAnExceptionWhenNullOrEmpty(source, dest);

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Delete or move the destination first if overwrite is intended: if (FileUtil.PathExists(dst)) FileUtil.DeleteFileOrDirectory(dst); then copy.
2. Use CopyFileOrDirectory only into a freshly created unique directory so the destination cannot pre-exist.
3. Switch to a copy primitive that allows overwrite (e.g. System.IO.File.Copy with overwrite:true) when you do not need the directory-recursion behaviour.

Example fix

// before
FileUtil.CopyFileOrDirectory(src, dst); // throws if dst exists
// after
if (FileUtil.PathExists(dst)) FileUtil.DeleteFileOrDirectory(dst);
FileUtil.CopyFileOrDirectory(src, dst);

if (FileUtil.PathExists(dst)) FileUtil.DeleteFileOrDirectory(dst);
FileUtil.CopyFileOrDirectory(src, dst);

static bool DestinationIsClear(string dst) => !FileUtil.PathExists(dst);

When it happens

Trigger: Calling CopyFileOrDirectory(src, dst) where dst already points to an existing file or directory. Re-running an import/copy step that did not clean up its prior output. Incremental build code that copies into a persistent target.

Common situations: Re-importing assets into a destination folder left over from a previous run. Build scripts copying template files into Library/ or a streaming-assets target that persists. CI re-runs that do not wipe the output directory first.

Related errors

• Failed to Copy File / Directory from '{0}' to '{1}'.
• Failed to Move File / Directory from '{0}' to '{1}'.
• Failed to delete directory '{0}'.
• FileUtil.OpenRead: Failed to acquire UDS content for '{path}
• Value cannot be null.

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/7734dac24c5f3370. Report an issue: GitHub.