CODEWITHSUNDEEP
windowsfor-loopbatch-filecmdescaping
user2863294
user2863294

Reputation: 472

Batch File: Prevent literal interpretation in a for /f loop

Currently I have a loop that runs through a list of items and copies them to a directory (archive). However, one of the items in the list (which has a global variable in the path-name) is being interpreted 'literally' (as text instead of code). I know usually you can just escape the line via (^^) to have it interpreted as code instead of text, but evidently I'm doing something wrong here, because it's not working...

The item in the my.list (with the escape in it) that is having issues is:

location\foo^^%date:~0,3%*.zip

The code I'm using is...

for /f "delims=" %%a in (my.list) do (
    echo "%%a"
)

Echo's

"location\foo^^%date:~0,3%*.zip"

Instead of

location\fooMON*.zip

Any help would be greatly appreciated.

Upvotes: 1

Views: 1128

Answers (1)

dbenham
dbenham

Reputation: 130819

You are confused as to when you need to escape a character.

Some characters have special meaning ("code" as you describe it). Often times you can escape the character such that it is interpretted as a literal (text) instead of "code".

The most frequent method to escape a character within Windows CMD.EXE is to prefix it with a single ^ character. Sometimes a string is parsed twice, which can require an escape sequence of ^^^, (or perhaps ^^ when dealing with ! when delayed expansion is enabled). More rounds of parsing require ever more ^ characters. It can quickly become confusing, and requires practice to get the hang of it.

But your situation is completely different - It cannot be solved by escaping. You have "code" within your FOR variable, and you want it to be interpreted as such. But instead, it is being interpreted as text. In order to understand why, you must understand the order in which various stages of batch parsing occur. You could refer to How does the Windows Command Interpreter (CMD.EXE) parse scripts?, but it is pretty advanced stuff that takes time to digest.

Here is a crude synopsis showing when various types of expansion occur. (Note - these step numbers do not match up exactly with the phase numbers of the linked answer)

1) Parameter expansion - %1
2) Normal variable expansion - %var%
3) FOR variable expansion - %%A
4) Delayed variable expansion - !var!
5) CALL expansion - repeat steps 1) and 2) if CALL involved

You want your %date:~0,3% string to undergo normal (percent) expansion. Your FOR loop reads the line of text verbatim, without any expansion. The first time the parser sees your "code" is at step 3) when the %%a FOR variable is expanded. You can see that this is already too late to get %date:~0,3% to expand the way you want.

You have two choices to solve your problem. But beware - each of these solutions potentially add new issues that may need to be solved.

I am assuming the ^^ is your naive attempt to force expansion of the embedded "code". The ^^ should be removed from your list file.

Option 1: Add an extra round of normal expansion by using CALL

for /f "delims=" %%a in (my.list) do call echo "%%a"

But now you have a potential problem that you might have a % literal in your list that you do not want to be expanded. Percents within batch scripts cannot be escaped with ^. Instead you escape a percent by doubling it as %%. So if you have percent literals in your list, they must be doubled.

Note that the original code that was posted with the question was significantly more complicated. It included an IF statement that referenced %%a. You cannot CALL an IF or FOR command. The solution is to CALL a subroutine, passing the value, and include the complex logic in the subroutine.

for /f "delims=" %%a in (my.list) do call :processValue "%%a" >>Logs\xfer.log
exit /b

:processValue
echo Attempting to archive %1...
if exist "c:\%~1" (
  echo f | xcopy "c:\%%a" "c:\Lucas\archive\%~1" /E /C /H /R /Y
  if %errorlevel%==0 (
    echo ...%1 added to archive for transfer
    echo.
  ) else (
    echo ERROR: %1 not added to archive
    echo.
  )
) else (
  echo ERROR: %1 Not found on client computer
  echo.
)

Option 2: Use delayed expansion

Enable delayed expansion, and change your list to use !date:~0,3! instead of %date:~0,3%. Delayed expansion occurs after FOR variable expansion, so it will be expanded properly.

setlocal enableDelayedExpansion
for /f "delims=" %%a in (my.list) do echo "%%a"

But now you have a potential problem that you might have a ! literal in your list that you do not want to be expanded. You can preserve ! literals by escaping them as ^!.

Upvotes: 5

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