Handling of variables in for-loop of a Windows batch file - batch-file

I've been investigating this a lot with threads on StackOverflow and the like, but although I feel I'm close to the solution, this problem is giving me headaches.
What I'm trying to do: When a specific external hard drive is connected (distinguished via VolumeSerialNumber over WMIC), the drive letter is found out, and mirroring is done via robocopy. The script is executed via double-click. This is what I have so far:
FOR /F "skip=1" %%i in ('wmic logicaldisk where VolumeSerialNumber^="XXXXXXXX" get deviceid 2^>nul') DO (
SET y=%%i
IF [%y%]==[] GOTO hdmissing
SET "backuphd=%%i"
GOTO endfor
)
:endfor
robocopy "C:\Users\Herbert\Documents" "%backuphd%\Backup\Documents" /MIR
ECHO Backup done
ECHO end
:hdmissing
ECHO Couldn't find external drive
:end
PAUSE
This way, the external HD is never detected (%y% is always an empty string). However, if I execute the script twice in the same console session, everything works as expected. But I want it to work at the first execution.
This is what I've tried so far:
Put SET y=dummy at the beginning of the script. The HD is always found, triggering a backup to C: if the HD is not actually connected (apparently SET y=%%i doesn't alter y?)
Change %y% to !y! - The HD is always found, again

Generation 3,576 of the delayed expansion problem, compounded by a contaminated environment.
There's no setlocal apparent, so y remains set in the environment after the first run - hence the 'later run characteristics different from first run' phenomenon.
Within a block statement (a parenthesised series of statements), the entire block is parsed and then executed. Any %var% within the block will be replaced by that variable's value at the time the block is parsed - before the block is executed - the same thing applies to a FOR ... DO (block).
Hence, IF (something) else (somethingelse) will be executed using the values of %variables% at the time the IF is encountered.
Two common ways to overcome this are 1) to use setlocal enabledelayedexpansion and use !var! in place of %var% to access the changed value of var or 2) to call a subroutine to perform further processing using the changed values.
The key in your case appears to be no setlocal enabledelayeexpansion and !y! - because !y! is just that - a literal string !y! unless delayedexpansion is invoked by the setlocal command.
(having said that,
IF [%%i]==[] GOTO hdmissing
would work just as well, as would
SET "y=%%i"
IF not defined y GOTO hdmissing
because if [not] defined var operates on the run-time value of var. "quoting the set arguments" ensures that any stray trailing spaces on the line are not included in the value assigned
)

As Magoo already pointed out, !y! doesn't work, since I forgot to enable Delayed Expansion. However, enabling it requires you to escape certain characters, which seemed quite irritating and tedious to me. It could be possible to just enclose the command in the FOR-loop with double quotes, as done in the two edits of this question, but I found out after solving it differently.
What I did was moving the block
IF [%y%]==[] GOTO hdmissing
SET "backuphd=%%i"
after :endfor. This way, it's outside of the for loop and %y% gets expanded accordingly.
Mind that this solution works only because I need just one item, and because of the programming flow.
Other useful approaches might be found in this question.
However, if you want to do the same thing: easier (though not as robust) solutions without WMIC might include
Putting a file with a specific name on the hard drive and checking for it with IF EXIST before backing up, hoping the user will not delete it, and the HD is connected to the same drive letter.
Putting the batch script on the drive itself and work with relative path names (optional: put a shortcut on the Desktop and hope again the drive is always under the same letter)

Related

cmd batch variable behavior is unintuitive

I'm using windows 10, running batch files through the command prompt window.
I can make things work, but I don't know why it works or why I can't do certain things:
set "file_list=a1 a2"
for %%a in (%file_list%) do (
echo %%a.py
)
This little piece of code works. I can build on it, BUT
Q1: I want to change the variable %%a to %%filename... but that doesn't work! I wondered if maybe filename were reserved, so I tried %%fname .
In this case I get the error:
%fname was unexpected at this time.
I can do a set fromm the command line and use a descriptive variable name, but it doesn't seem to work when looping. (I did it with the %file_list% variable above!) So how come I can only use a single character for a loop variable? Is there some way around that?
Q1a. This makes me think that the loop index variable is a different kind of variable that the ones in set commands. Is that correct? If so, is there a link that clearly and concisely explains the difference?
Q2. I notice the loop index variable is %%a, instead of a or %a or %a% . I never would have guessed this. The web sites I've looked at have just said, do this. But I can't see any explanation of why, except that the first percent is an escape. Okay. That doesn't really explain anything. It just means "this is how you do it." The error message when I use one percent sign is interesting.
set "file_list=a1 a2"
for %a in (%file_list%) do (
echo %a.py
)
"file_list) was unexpected at this time."
So I can vaguely see that maybe something isn't being escaped correctly. Why does that % in the %a need to be escaped, so it becomes %%a ?
A for meta-variable must consist of % (in Command Prompt) or %% (in a batch file) and a single character (case-sensitive letter), like %a or %%a. You cannot define %filename or %%filename.
Loop variables only exist within the respective for loop. Do not confuse such loop variables with normal environment variables, like %TEMP%, for example, which are available globally.
There are these things marked by %-signs:
%-escaping (only applicable for batch files), so %% denotes one literal %-sign;
command line arguments/parameters (only applicable for batch files, obviously), like %1;
immediately expanded environment variables*, like %TEMP%;
for meta-variables, like %a (in Command Prompt) or %%a (in batch files), which are specific to the for command, so they do not exist outside of the related loop context;
%-escaping (1.) happens before expanding for meta-variables (4.), hence actually the for command receives a loop variable like %a.
Then environment variables (3.) are treated differently in Command Prompt and in batch files: the former keeps undefined variables literally, the latter removes them.
The detailed parsing rules can be found in this post, which have been implemented by Microsoft (or IBM?) that way in order to be able to distinguish between the different %-things, so at the end it was their decision, therefore you have to ask them for the exact reason…
*) There is also something like delayed environment variable expansion, but this uses !-signs to mark the variables, like !TEMP!, and this is something that happens after all the %-sign expressions have been parsed.

How to output multiple lines from a FINDSTR to a variable

It's no surprise that the official documentation doesn't really help in the matter of understanding how does the command process the result of a command instead of a filelist neither why is it even called 'FOR'. Yes I already know Stack Overflow is full of similar question but apparently, since batch scripts are influenced by so many
"breaking" factors that, even as a non-batch experienced programmer, it is difficult not to get lost in the thousands exceptions and do-nots which may affect the result.
My objective, aside from learning from the best answer possible, is to formulate a generic enough question to represent the matter which is probably the most common task including the FINDSTR command:
THE QUESTION:
How do I get the output of a FINDSTR in a way that allows me to compute every result line one at the time
possibly INSIDE the loop?
The most 'generic' (batch bs-proof if you know what I mean) example I can make is the following:
Let's say this is secret_file.txt
some not interesting line
A very interesting line = "secret1";
some not interesting line
A very interesting line = "secret2";
some not interesting line
A very interesting line = "secret3";
some not interesting line
Now with the findstr command I can output every "secret" line like this:
findstr /R /C:"secret.\"" secret_file.txt
A very interesting line = "secret1";
A very interesting line = "secret2";
A very interesting line = "secret3";
But this result is just useless without further parsing right? I could have used ctrl-F over any text reader/editor
for this matter, anyway, let's say I now want to output every line ONE AT THE TIME so that I can compute it, for
example, saving every secret to a variable then using that variable somehow
(it doesn't really matter how, we can just echo it to keep things simple).
Now, everybody agrees on the fact that for this kind of task, a FOR loop is needed.
Quoting https://ss64.com/nt/for.html on the syntax, my script.bat should looks like this:
#echo off
FOR /F %%A IN ('findstr /R /C:"secret.\"" secret_file.txt') DO ECHO Batch script language is completely fine, good job Microsoft!
This just doesn't even give any output, can someone explain me why? My hypothesis was that the output from the findstr command
is in a non-compatible format with the FOR command, not like I could check or something since the source is closed and the
documentation doesn't even bother defining the word String.
I'm ready to provide any details and even edit the question to be more visible to the wanna be Microsoft-forsaken batch scripters out there.
Using "tokens=*" to strip off leading spaces this batch uses a counter to create a (pseudo) array secret[]
:: Q:\Test\2018\12\04\SO_53614102.cmd
#Echo off
set Cnt=0
FOR /F "tokens=*" %%A IN (
'findstr /R /C:"secret.\"" secret_file.txt'
) DO (
set /a Cnt+=1
call Set Secret[%%Cnt%%]=%%A
)
Set Secret[
Sample output:
> SO_53614102.cmd
Secret[1]=A very intersting line = "secret1";
Secret[2]=A very intersting line = "secret2";
Secret[3]=A very intersting line = "secret3";
As variables in a (code block) are expanded at parse time,
delayed expansion is requiered (here through a call and doubled %%)

Do batch scripts treat variables differently in blocks?

I'm running a batch file which updates some variables, notably %PATH%. My environment has a known bug where on of the directories in %PATH% is quoted, i.e.
PATH=c:\windows;...;"c:\program files\foo"\bin;c:\program files\...
I have a script which appends to PATH. When I do it inside an IF block, I get an error, e.g:
IF "1"=="1" (
SET "PATH=%PATH%;c:\foo"
)
Gives the error
\Microsoft was unexpected at this time.
Where \Microsoft is obviously a fragment from one of the directories in %PATH%.
I don't get the error if the SET is not within a conditional block. Why is this?
Edit: It seems that this has more to do with the fact that PATH also contains parenthesis. Here's a better example of the issue:
C:\temp>SET "FOO=C:\Program Files (x86)\;foo"
C:\temp>ECHO %FOO%
C:\Program Files (x86)\;foo
C:\temp>IF "1"=="1" ( ECHO %FOO% )
\ was unexpected at this time.
C:\temp>IF "1"=="1" ECHO %FOO%
C:\Program Files (x86)\;foo
So my question is really, why does it break if it's in the paren-delimited block?
JosefZ properly identified the problem with ) in the path, but his suggested solution of removing all quotes is not safe.
Any path within the PATH variable may include ;, !, &, ) and/or ^, all of which can cause various issues when using normal %PATH% expansion.
There may be some paths with & or ) etc. quoted, as well as some unquoted paths with problem characters, so both %PATH% and "%PATH%" can fail.
The only guaranteed safe way to expand PATH is via delayed expansion, but you want the new value to survive the ENDLOCAL. What to do? . . .
. . . FOR /F and delayed expansion toggling to the rescue :-)
if "1"=="1" (
setlocal enableDelayedExpansion
for /f "eol=: delims=" %%P in ("!path!") do (
endlocal
set "path=%%P;c:\foo"
)
)
Simplistic implementation of PATH extension via code like set path=%path%;c:\foo,
or set "path=%path%;c:\foo" is rampant, but it is not safe. By and large, people do not realize the subtle complexities involved with PATH management.
If you are ever trying to modify the PATH variable in a batch script that can be released into the wild, then you should always use a safe method like the one I have shown above.
The problem becomes even more complex if you want to conditionally append a path to PATH if and only if path is not already there. See How to check if directory exists in %PATH%? for a list of potential issues, as well as a fairly robust solution.
SET "PATH=%PATH:"=%;c:\foo"
should fix the problem, since the quoes are irrelevant
Caution: This may not be true if a path-entry contains ";". In that case, you should rename the directory to something sensible.
You are right that this has more to do with the fact that PATH also contains parentheses. Next example shows the issue unambiguously:
==> ( set "varName=var"value(s) with"space(s) and"right parentheses"" )
with"space(s) and"right was unexpected at this time.
==> ( set varName=var"value(s) with"space(s) and"right parentheses" )
and"right parentheses" was unexpected at this time.
==>
Read answers to How does the Windows Command Interpreter (CMD.EXE) parse scripts? for explanation.
I can see the only solution: correct (adjust) your path variable once for always by removing all " double quotes as follows (check user variable path as well if present). Restart required.
Just remove the outer quotes in your setting of the path variable. They're not required, by any means. Certainly not in this instance, where you have quotes being used internally within those quotes. The quotes should be inside your path variable, not outside the whole thing.
SET PATH=%PATH%;c:\foo
To further how it should be done, here's some additional examples to clarify...
SET PATH=%PATH%;C:\foo
SET PATH=%PATH%;"C:\Some Folder With Spaces In It"
SET PATH=%PATH%;"C:\Program Files\Foobar Inc Software"
But never...
SET "PATH=%PATH%;SomePath"

Variable in variable batch

Alright, I need help here. I have done this before where you have variable1 (let's say it's eat1=apple), variable2 (this is eat2=orange), and variable3 (appaleorange=apple and orange). I need it to do this:
echo Apple:%eat1%
echo Orange:%eat2%
echo Apple & Orange:%eat1%%eat2%
Now, you can see my problem. That above script wouldn't show the word and, only appleorange. That isn't my script and the reason I need this is because I have multiple variables with numbers in them. I have done this before and I forgot how... I know you can do a call and then multiple %'s.
In this case I want fterm variable to be fterm (not sure how to have it in there and not be a variable) and stermnum as a number that will be changed often on other parts of the script.
My code:
set stermnum=1
call set exsternum=%%fterm%%stermnum%%%
echo Selected term:%stermnum% ^(%exsternum%^)
Does anyone know what to do?
Thanks and sorry it was long :P
~Edit:I found it out... If it helps anyone I did:
call set exsternum=%%fterm%stermnum%%
Sorry for posting this even though I figured it out so fast
The OP appended a solution to the question, but it does not relate to the original question scenario, and it still has a bug.
Here is the OP's solution in terms of the original scenario:
set "eat1=apple"
set "eat2=orange"
set "appleorange=apple and orange"
call echo %%%eat1%%eat2%%%
For the actual code, I believe the OP wants to access an array of variables named fterm1, fterm2, fterm3, etc. And the number suffix is in a variable named stermnum.
call set exsternum=%%fterm%stermnum%%%
If fterm is itself a variable containing the base name of the array, then the solution becomes:
call set exsternum=%%%fterm%%stermnum%%%
But CALL is inefficient - Probably not noticeable with a single CALL, but it becomes painfully slow if executed thousands of times in a loop.
There is a much faster solution using delayed expansion. Delayed expansion must be enabled prior to being used.
Original scenario:
setlocal enableDelayedExpansion
set "eat1=apple"
set "eat2=orange"
set "appleorange=apple and orange"
echo !%eat1%%eat2%!
Actual code, interpretation 1:
setlocal enableDelayedExpansion
REM additonal code ...
set exsternum=!fterm%stermnum%!
Actual code, interpretation 2:
setlocal enableDelayedExpansion
REM additonal code ...
set exsternum=!%fterm%%stermnum%!

How to get a the directory path from a variable in a cmd batch file

Within my batch file I have a variable that contains a file path:
SET VAR1=C:\Folder1\Folder2\File.txt
I would like to extract on the directory structure and retreive:
C:\Folder1\Folder2\
I have read threads like this where I need to use %~dp0 where 0 I believe is passed as a parameter. I have tried %~dpVAR1 but that doesn't work. How can I get the output I'm looking for, but with a variable containing the file path?
Also, to make matters difficult, I have to perform all of this within an IF condition which means that once the variable is declared, I will need to refer to it with ! instead of % (I have declared setlocal enableextensions enabledelayedexpansion at the beginning of my script to allow for this).
Any help is much appreciated!
Thanks!
Andrew
You are attempting to use parameter expansion syntax on an environment variable - that cannot work. But it is relatively easy to do what you want.
Using a CALL (relatively slow):
(...
call :getPath "!var!" var
...
)
exit /b
:getPath
set "%2=%~dp1"
exit /b
Using FOR, assuming the variable does not contain any wildcards (fast)
(...
for %%F in ("!var!") do set "var=%%~dpF"
...
)
Using FOR, if the variable may contain wildcards (also fast)
(...
for /f "delims=" %%F in ("!var!") do set "var=%%~dpF"
...
)
Note 1: If the variable does not contain the full path, then all the solutions will attempt to resolve the name into an absolute path and will return the full absolute path. For example, if var contains foobar\test.txt, then the solutions will include the full path to the current directory, even if the file is not found. Something like c:\pathToCurrentDirectory\foobar\.
Note 2: All solutions above will remove all quotes from the path.
Note 3: A path could include the ! character, which will cause problems when expanding %~dp1 or %%~dpF because you have delayed expansion enabled. The delayed expansion will corrupt both ^ and ! if the value contains !. There is a solution that involves protecting both ! and ^. Here is a demonstration applied to the last solution above. The protection requires normal expansion, and since you are within a code block, it requires at least one CALL. It could be done without a subroutine, but it is easier with a subroutine. The subroutine assumes the variable is named var.
(...
call :getPath
...
)
exit /b
:getPath
set "var=!var:"=!"
set "var=!var:^=^^^^!"
set "var=%var:!=^^^!%" !
for /f "delims=" %%F in ("!var!") do set "var=%%~dpF" !
exit /b
I do believe (once again) many questions are on the same topic (string constraints, or splitting strings).
Instead of giving you the whole code, I'm going to give you a template and explain why %~dpVAR! didn't work.
Firstly, why %~dpVAR! did't work.
Before I get into modifiers, let's discuss parameters. You may know that batch files can parse parameters to each other. These parameters can be called by using a single percent sign (%) in front of the numbers 0-9. As far as I'm aware (someone might have made a way for more to be parsed), only 9 parameters can be parsed. You may think that is wrong (there's 10 parameters right?). Parameters 1-9 are parsed to the batch file (or function within one), %0 is the file path of the batch file (or function name). If you look, %~dp0 shares some (not really) resemblance to %0. This will be discussed below.
Secondly, the term %~dp0 has modifiers in it. Modifiers are things that modify variables (only in the case of parameters and those declared in for loops, you know the ones with double percent signs like %%i) and parameters. The modifier d expands the parameter to a drive letter only while p expands the parameter to a path only. You may think that these would contradict themselves, but parameters can be combined to create extremely wacky formats.
So, as you can see, you attempt at replacing 0 with your variable name failed because it's not specified for those sort of things.
Now, on to the template.
You can constrain variables (and put them into other variables) like this:
set variable=!variable:~offset,amount!
Don't worry if that seems confusing, I'm about to explain the components.
Firstly, notice that there is no /a switch. This is because this is not a mathematical function (don't really know why I added this). So, before I explain it, here's an example of what it would do to a variable name numbers that has the value of 0123456789.
set numbers=!numbers:~5,1!
By using that line of code, numbers would now equal 5. This is because it is recreating the variable with a smaller version of the original value (gee this is hard to explain). As you can see, there is a 5 where offset was on the template above. This is because it is skipping the first 5 characters and setting the variable as the next amount, or 1 character (I really hope you're getting this).
So basically, it sets a variable as a shorter value of a different (or the same) variable determined by the offset and the amount of characters to contain in it.
I really hope this helps because I probably wouldn't understand a word of this.
Can someone redirect this poor guy to a link explaining this better (I tried, ok!)?
Complete example of extracting paths from variable:
#echo off
set /p Fullpath="Specify full path: "
call :getPath %Fullpath% filename folder
echo %filename%
echo %folder%
pause
exit /b
:getPath
set "%2=%~nx1"
set "%3=%~dp1"
exit /b
Would this work:
SET VAR1=C:\Folder1\Folder2\File.txt
echo %var1%
Where Echo is the name of your exe.
%CD% may work as well: Echo %CD%

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