How to extract extension of input file parameter using Windows batch script

Given this batch script - how do I isolate filename and extension, like in the output given:

@echo off
REM usage split.bat <filename>
set input_file="%1"
echo input file name is <filename> and extension is <extension>

c:\split.bat testfile.txt
input filename is testfile and extension is txt

That is - what's the correct syntax for <filename> and <extension> in this code?

Solution 1:

How do I isolate filename and extension from %1?

Use the following batch file (split.bat):

@echo off 
setlocal
REM usage split.bat <filename>
set _filename=%~n1
set _extension=%~x1
echo input file name is ^<%_filename%^> and extension is ^<%_extension%^>
endlocal  

Notes:

• %~n1 - Expand %1 to a file Name without file extension.

• %~x1 - Expand %1 to a file eXtension only.

• < and > are special characters (redirection) and must be escaped using ^.

Example usage:

> split testfile.txt
input file name is <testfile> and extension is <.txt>

Further Reading

• An A-Z Index of the Windows CMD command line - An excellent reference for all things Windows cmd line related.
• parameters - A command line argument (or parameter) is any value passed into a batch script.
• redirection - Redirection operators.
• syntax - Escape Characters, Delimiters and Quotes.