Problems reading simple numeric values from files in Windows batch files - windows

Question

My colleague and I have been pulling our hair out all day over this.
We have a simple Windows batch file. We want it to read from a text file whose file path we are generating programmatically, take the single numeric value in this file, and compare it to a local variable. But we're getting completely inexplicable behavior.
The file contains a single scalar number, such as the number 2. Here's the code:
ThisAppFlagFileName=foo.txt
if not exist "%HOMEPATH%\ourcompanyname\%ThisAppFlagFileName%" (
ECHO do something here
) else (
SET /P InstalledVersion=<"%HOMEPATH%\ourcompanyname\%ThisAppFlagFileName%"
ECHO We think the file contains: %InstalledVersion%
IF %InstalledVersion% GEQ %ThisVersionInstallDataNum% (
ECHO Version %ThisVersion% of the %ThisAppVisibleName% has already been installed for this user; exiting.
GOTO TheEnd
)
)
:TheEnd
Echo END
We keep getting an error reading 2 was unexpected at this time. So we inserted some trace message and, just in case the else was problematic, stuck to two different if statements:
ThisAppFlagFileName=foo.txt
if not exist "%HOMEPATH%\ourcompanyname\%ThisAppFlagFileName%" (
ECHO do something here
)
ECHO Trace Message 1 before IF
if exist "%HOMEPATH%\ourcompanyname\%ThisAppFlagFileName%" (
ECHO Trace Message 2 after IF before CD
SET /P InstalledVersion=<%HOMEPATH%\ourcompanyname\%ThisAppFlagFileName%"
ECHO We think the file contains: %InstalledVersion%
IF %InstalledVersion2% GEQ %ThisVersionInstallDataNum% (
ECHO Version %ThisVersion% of the %ThisAppVisibleName% has already been installed for this user; exiting.
GOTO TheEnd
)
)
:TheEnd
Echo END
And we see only the first trace message (before the if statement), and not the second trace message. So our conclusion is that somehow the content of the file is being interpolated into the line if exist "%HOMEPATH%\ourcompanyname\%ThisAppFlagFileName%", but of course we don't understand why the first if not exist works but the second doesn't.
Can anyone spot the mistake, please? Environment is Windows 7 cmd.exe window, but we are hoping to deploy to both Windows 7 and Windows XP.

Answer 1

The issue here is that the entire IF expression is evaluated before the SET /P statement within it can be executed. InstalledVersion is not set yet, and so this invalid expression is evaluated:
IF GEQ 2 (
Nothing inside of the IF expression executes because it cannot be completely evaluated.
A solution is to enable delayed expansion and replace %InstalledVersion% with !InstalledVersion!, as described in this post.
You can also restructure the code so the GEQ comparison happens after the IF expression.

Answer 2

Your code have several errors. The first line:
ThisAppFlagFileName=foo.txt
missed a set command, so it is tryed to be executed as ThisAppFlagFileName command. This mean that ThisAppFlagFileName variable is NOT defined in your program, so InstalledVersion variable is never read from the file.
All references to InstalledVersion variable must use Delayed Expansion, that is, enclose they between exclamation marks instead percents and include setlocal EnableDelayedExpansion command at beginning of your program.
setlocal EnableDelayedExpansion
set ThisAppFlagFileName=foo.txt
if not exist "%HOMEPATH%\ourcompanyname\%ThisAppFlagFileName%" (
ECHO do something here
) else (
SET /P InstalledVersion=<"%HOMEPATH%\ourcompanyname\%ThisAppFlagFileName%"
ECHO We think the file contains: !InstalledVersion!
IF !InstalledVersion! GEQ %ThisVersionInstallDataNum% (
ECHO Version %ThisVersion% of the %ThisAppVisibleName% has already been installed for this user; exiting.
GOTO TheEnd
)
)
:TheEnd
Echo END
You must be aware that all variables that are modified inside parentheses must also be enclosed in exclamation marks instead percent signs. Search for "delayed expansion" for details.