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Asked: 2021-11-10T11:35:41+00:00 In:

User Prompt To Set Drive Letter

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hi,

i’m trying to semi-automate a batch file of mine for file backups. i’m using an ‘if’ statement to determine (by comparing to %~d0) if the batch is being run from the backup drive (so use %~d0) or the C: drive (so prompt user for drive letter).

my script seems to work fine from the backup drive, but is ‘funny’ if run from the C: drive.

‘funny’ means that i have to input the drive letter three times before the letter is actually ‘set’.

i have added an echo of the resulting drive letter variable, and in each of the first three trys, this is what i get:

1) your drive letter is:
2) your drive letter is: :
3) your drive letter is: i:
+) your drive letter is: i:

the other quirk is that, if i comment out the if statement, and have JUST the user prompt, the variable is set fine.

here is the script:

 

::determine if program is run from local or other drive
IF %~d0==C^: (
	ECHO.
	ECHO ============================
	ECHO START
	ECHO.
	ECHO Please attach the backup drive.
	ECHO.
	:: set drive letter manually
	SET /P L="Type the drive letter, then press ENTER: "
	:: the caret character is used before special symbols
	SET D=%L%^:
	ECHO Your drive letter is: %D%
	PAUSE
	CLS
) ELSE (
	::set drive letter of batch file automatically
	SET D=%~d0
)

this is my first ever batch script, but this quirk has got me stumped. has anyone experienced this before? can anyone see where i’ve gone wrong?

thanks in advance,
agnieszka.

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    2 Answers

    1. I don’t think you need special handling of colon. But use delayed expansion to make IF blocks work.
      ================================

      @echo off & setLocal EnableDELAYedeXpansion
      IF %~d0==C: (
      SET /P L=”Type the drive letter, then press ENTER: ”
      SET L=!L!:
      ECHO Your drive letter is: !L!
      ) ELSE (
      SET D=%~d0
      )

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    2. Whenever you’ve got a series of commands inside brackets (i.e. in your case it’s the IF-block) then those commands are loaded into the interpreter all at once, and all %variable% expansions are performed before the commands are executed. So in your SET D=%L%^: the %L% gets expanded to the value of L at the start of the IF block, and does not see the changed value after the preceding SET/P command.
      To fix this, you need to use delayed expansion. At the start of your batch file, put

      SETLOCAL EnableDelayedExpansion
      and use !L! instead of %L% (and of course !D! instead of %D%). Type SET /? for more details.

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