What are common pitfalls or gotchas with opening files (open, three-arg open)?

When working with file operations in Perl, particularly with the `open` function, there are several common pitfalls or gotchas that developers might encounter. Understanding these can save you from unexpected behavior and bugs in your code.

• File Permissions: Always check that your script has the necessary permissions to read from or write to a file. If you attempt to open a file without the proper permissions, your script will fail.
• Using Three-Argument Open: It's a good practice to use the three-argument version of `open`, which allows you to specify the mode and filehandle more clearly, thus avoiding some common mistakes.
• Error Handling: Always include error handling when opening files. This can prevent your script from failing silently. Use `die` or `warn` to handle errors appropriately.
• Filehandles Not Closed: Forgetting to close filehandles can lead to memory leaks and other unexpected behaviors. Always ensure filehandles are closed after operations are complete.
• Buffering Issues: Be aware of how Perl handles buffering when reading from or writing to files. Sometimes you may need to flush the buffer to see the effects of your writes immediately.

By being aware of these issues, you can avoid common mistakes and write more reliable Perl scripts when handling file operations.