01-2-File-extensions-Wildcards.md

🧾 File Extensions and Wildcards

• When working with batch scripts in Windows, two often-overlooked but fundamental tools are:

  • 📄 File Extensions — which determine how files are interpreted and handled

  • ✳ Wildcards — which let you select multiple files dynamically

  Together, they let you create powerful scripts that are flexible, dynamic, and scalable — perfect for file processing, cleanup routines, and automated workflows.

  📂 Understanding File Extensions in Batch

  In Windows, file extensions (e.g., .txt, .log, .exe) define how the OS treats the file. In batch scripting:

  • You often filter files by extension using FOR, IF EXIST, DEL, COPY, etc.
  • Extensions are not case-sensitive
  • To reference just the extension or filename, use variable modifiers

  ✅ Common File Extensions in Batch Contexts

  Extension	Use Case
  .bat	Batch script
  .cmd	Modern batch script (like .bat)
  .txt	Logs, data, or configuration
  .log	Logs from apps or services
  .exe	Executables
  .zip	Archives or backups

---

✳️ Wildcards in Batch Scripts

• Wildcards let you match multiple files using patterns.

  ✅ Supported Wildcards

  Wildcard	Meaning
  *	Zero or more characters
  ?	Exactly one character

  ---

  🔹 Examples

  DIR *.txt          :: All files ending in .txt
  DIR data?.csv      :: data1.csv, dataA.csv, but NOT data10.csv
  DEL report*.log    :: report1.log, report_final.log

  ---

  🛠️ Using Wildcards with Commands

  🧹 Deleting Multiple Files

  DEL /Q *.tmp

  Deletes all .tmp files in the directory without confirmation.

  ---

  📝 Copying Files by Extension

  COPY *.txt D:\Backup\

  Copies all .txt files to the backup directory.

  ---

  🌀 Processing Files in a Loop

  FOR %%F IN (*.log) DO (
      ECHO Processing: %%F
  )

  This loop processes all .log files in the current folder.

  You can also apply filters:

  FOR %%F IN (report_202?.log) DO (
      ECHO Match: %%F
  )

  ---

  🔍 File Matching: FOR /R for Subdirectories

  FOR /R %%F IN (*.txt) DO (
      ECHO Found: %%F
  )

  • Recursively finds all .txt files in current and subfolders.

---

🧠 Variable Modifiers for File Extensions

• Inside a FOR loop, you can extract file parts:

  Modifier	Meaning
  %%~nF	Name only (no extension)
  %%~xF	Extension only (with dot)
  %%~dpF	Drive + path
  %%~nxF	Name + extension

  FOR %%F IN (*.log) DO (
      ECHO Name: %%~nF, Extension: %%~xF
  )

---

🧪 Real-World Use Cases

1. 📦 Batch Rename .txt → .bak

   FOR %%F IN (*.txt) DO (
       REN "%%F" "%%~nF.bak"
   )

2. 📁 Move Only .zip Files to Archive

   MOVE *.zip D:\Archives\

3. 📄 Count .log Files in a Folder

   SET COUNT=0
   FOR %%F IN (*.log) DO SET /A COUNT+=1
   ECHO Log file count: %COUNT%

4. 🧹 Clean Up Old Backups

   DEL /S /Q backup_*.zip

   Deletes all ZIP files starting with backup_ in current and subfolders.

5. 💡 Bonus: Conditional File Extension Checks

   You can conditionally act on file extensions:

   FOR %%F IN (*) DO (
       IF /I "%%~xF"==".log" (
           ECHO Found log file: %%F
       )
   )

   Use /I for case-insensitive comparison.

---

⚠️ Limitations and Gotchas

Issue	Workaround
Cannot use wildcards with REN destination	Use FOR loop with modifiers
Wildcards in IF EXIST require care	Avoid quotes: IF EXIST *.txt (not IF EXIST "*.txt")
No regex support	Use PowerShell or hybrid script for complex filters

🧠 Summary

Task	Batch Pattern
Match all .txt files	*.txt
Match any one-letter name	?.txt
Process by extension	FOR %%F IN (*.ext)
Get name only	%%~nF
Get extension only	%%~xF