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windowsbatch-file
Harry Johnston
Harry Johnston

Reputation: 36328

Are environment variables expanded when searching PATH?

This question expands on the comments on this deleted answer. I claimed that an unexpanded variable reference in the PATH would not be expanded when searching for an executable, but Ken said he didn't see the same behaviour that I did.

Note that the ordinary situation is subtly but critically different: subject to certain conditions, environment variables are automatically expanded when the PATH environment variable is built from the information in the registry. I'm talking about the case where, for one reason or another, this hasn't happened, so the actual environment block of the cmd.exe process contains a PATH which still has environment variable references in it.

Here is the code I built to test this behaviour:

md test1
echo echo hello! > test1\test1.cmd

set TESTPATH=%cd%\test1

set percent=%%

set PATH=c:\windows\system32;c:\windows;c:\windows\system32\Wbem;%percent%TESTPATH%percent%

set PATH

set TESTPATH

test1

cmd /c test1

start test1.cmd

and this is the result on my machine:

C:\working\testpath>test

C:\working\testpath>md test1

C:\working\testpath>echo echo hello!  1>test1\test1.cmd

C:\working\testpath>set TESTPATH=C:\working\testpath\test1

C:\working\testpath>set percent=%

C:\working\testpath>set PATH=c:\windows\system32;c:\windows;c:\windows\system32\
Wbem;%TESTPATH%

C:\working\testpath>set PATH
Path=c:\windows\system32;c:\windows;c:\windows\system32\Wbem;%TESTPATH%
PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC;.py;.pyw

C:\working\testpath>set TESTPATH
TESTPATH=C:\working\testpath\test1

C:\working\testpath>test1
'test1' is not recognized as an internal or external command,
operable program or batch file.

C:\working\testpath>cmd /c test1
'test1' is not recognized as an internal or external command,
operable program or batch file.

C:\working\testpath>start test1.cmd
The system cannot find the file test1.cmd.

What is the expected behaviour? Does it vary depending on the version of Windows and/or other factors?

Upvotes: 1

Views: 492

Answers (1)

Aacini
Aacini

Reputation: 67216

There are two entirely different points of view in this question:

  • Q: How to expand the values of variables embedded in another one? This point is not specific to PATH variable, but works on anyone.

A: Enclose the names of the variables in exclamation marks and enable delayed expansion when you want to expand such values:

@echo off
setlocal EnableDelayedExpansion

set TESTPATH=%cd%\test1
set "PATH=c:\windows\system32;c:\windows;c:\windows\system32\Wbem;^!TESTPATH^!"
set PATH
echo PATH=%PATH%
  • Q: Does cmd.exe such delayed expansion when it use PATH to locate an executable file?

A: No. cmd.exe uses the values in PATH variable as they appear, with no further processing. Any special character that may appear in PATH, like percents or exclamation-marks, are taking literally.

Upvotes: 1

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