On: Shhh: The Undocumented DOS Commands (1999)

[pan69]

I have been revisiting the DOS eco-system lately and I have run into a problem. I can't remember how to ECHO a variable set in AUTOEXEC.BAT. E.g, to ECHO the BLASTER variable, I've tried ECHO BLASTER, ECHO $BLASTER, ECHO $BLASTER$, ECHO %BLASTER, etc.. But nothing. Somehow a Google search didn't turn up anything. I'm starting to wonder if it was it even possible to do this and that my memory is incorrect?

Cool list by the way. Bookmarked!

[skissane → pan69]

ECHO %BLASTER%

You almost had it, you just need two percents.

It is the same syntax as Windows cmd.exe currently uses

[pan69 → skissane]

OK, so I tried this, but ECHO %PATH% just outputs %PATH%. I'm running DOS 6.22 on a 286. Same thing happens for any other variable defined in AUTOEXEC...

[morsch → pan69]

"In DOS I believe that %var% expansion only works in batch files, not at the command line directly."[1] That worked for me in an emulator.[2]

[1] https://stackoverflow.com/questions/28021862/echo-variable-s...

[2] https://jamesfriend.com.au/pce-js/ibmpc-games/

[pan69 → morsch]

Confirmed. It doesn't work directly from the prompt, only within a batch file. I think might work on a DOS 7 prompt (Win95 >) though, not sure, I don't have a Windows machine hooked up atm. Maybe that's where my memory is from...

Thanks!

[brirec → pan69]

SET BLASTER

No “=” — `SET BLASTER=` will erase the variable, and of course `SET BLASTER=f00` will set it to “f00”. N.b., `SET FOO` will display all variables beginning with “FOO” and remember that DOS/Windows vars aren’t case sensitive.

[jimmyswimmy → pan69]

It was % to indicate environment variables.

echo %PATH%

Should work, as long as that variable is in scope, which it should be on an old MSDOS platform with a single thread.

[TeMPOraL → jimmyswimmy]

Environmental variables have scopes?

[pan69 → TeMPOraL]

Its probably that variables defined in AUTOEXEC are "global" scope, i.e. can be referenced in any other batch file, but variables defined within a batch file other than AUTOEXEC only exist within the scope (context) of that batch file. But, I haven't tested this...

[4cao → TeMPOraL]

I think in DOS they were all global in scope. SETLOCAL appeared with Windows NT (cmd.exe), not sure which version (I didn't use the early ones).