问题
I'm really wondering why my string replacement procedure works when parsing text files containing any special characters including exclamation marks. I expected that delayed variable expansion would switch off special meaning of ampersand, percent sign etc. but will fail instead for exclamation marks...
Code:
@echo on & setlocal ENABLEEXTENSIONS
set "InFile=%~1"
set "OutFile=%~2"
set "Replace=%~3"
CALL :ParseCue "%%InFile%%" "%%OutFile%%" "%%Replace%%"
endlocal &GOTO:EOF
:ParseCue
@echo on & setlocal ENABLEEXTENSIONS DISABLEDELAYEDEXPANSION
set "FileToParse=%~1"
set "OutputFile=%~2"
set "NewExtension=%~3"
for /F "usebackq tokens=* delims=" %%a in ("%FileToParse%") DO (
set "line=%%a"
@echo on & setlocal ENABLEEXTENSIONS ENABLEDELAYEDEXPANSION
set "line=!line:.wav=%NewExtension%!"
echo(!line!>>"%OutputFile%"
endlocal
)
endlocal &GOTO:EOF
InputFile.txt:
This a test for parsing lines with special characters
Rock & Roll.wav
Rock & Roll!.wav
Special | < > ~ \ ²³ { [ ] } ! " ´ ' ` üäö @ ; : € $ % & / ( ) = ? chars.wav
Command line syntax:
D:\Users\Public\Batch\YAET>parse.bat "InputFile.txt" "OutputFile.txt" ".flac"
OutputFile.txt:
This a test for parsing lines with special characters
Rock & Roll.flac
Rock & Roll!.flac
Special | < > ~ \ ²³ { [ ] } ! " ´ ' ` üäö @ ; : € $ % & / ( ) = ? chars.flac
EDIT / Supplement:
After 1 1/2 years I had to use this code snippet again. See two additional examples handling poison chars. First one with temporary enabled delayed expansion again (see Ansgars answer), second one using CALL. Both will parse path and name of non-empty files in and below current directory, but without trailing drive letter and path to current dir.
Example #1 (Enclosing double quotes in set "File=!File..." and echo "!FILE!">>... are not required):
@echo off & setlocal ENABLEEXTENSIONS DISABLEDELAYEDEXPANSION
del NonEmptyFiles.txt >NUL 2>&1
echo Searching non-empty files in and below current directory ...
for /f "tokens=*" %%I in ('dir /s /b /a:-D') do (
if not %%~zI==0 (
set "File=%%I"
setlocal ENABLEDELAYEDEXPANSION
set "File=!File:%cd%\=!"
echo "!File!">> NonEmptyFiles.txt
endlocal
)
)
echo Done. See NonEmptyFiles.txt.
endlocal &goto:EOF
Example #2 (slower, enclosing double quotes required):
@echo off & setlocal ENABLEEXTENSIONS DISABLEDELAYEDEXPANSION
del NonEmptyFiles.txt >NUL 2>&1
echo Searching non-empty files in and below current directory ...
for /f "tokens=*" %%i in ('dir /s /b /a:-D') do (
if not %%~zi==0 (
set "File=%%i"
call set "File=%%File:%cd%\=%%"
call echo "%%File%%">> NonEmptyFiles.txt
)
)
echo Done. See NonEmptyFiles.txt.
endlocal &goto:EOF
Files and folders for testing:
D:\Martin\Any & Path>dir /s /b /a:-D
D:\Martin\Any & Path\Hello! World!.txt
D:\Martin\Any & Path\Rock & Roll\!File! !!File!!.txt
D:\Martin\Any & Path\Rock & Roll\%File% %%File%% %%I.txt
D:\Martin\Any & Path\Rock & Roll\Poison! !§$%&()=`´'_;,.-#+´^ßöäüÖÄÜ°^^#.txt
D:\Martin\Any & Path\Rock & Roll\SizeZero.txt
Output:
D:\Martin\Any & Path>stringinforloop.bat
Searching non-empty files in and below current directory ...
See NonEmptyFiles.txt. Done.
D:\Martin\Any & Path>type NonEmptyFiles.txt
"Hello! World!.txt"
"Rock & Roll\!File! !!File!!.txt"
"Rock & Roll\%File% %%File%% %%I.txt"
"Rock & Roll\Poison! !§$%&()=`´'_;,.-#+´^ßöäüÖÄÜ°^^#.txt"
Enjoy batching! Martin
回答1:
That's because you enable delayed expansion after set "line=%%a":
set "line=%%a"
@echo on & setlocal ENABLEEXTENSIONS ENABLEDELAYEDEXPANSION
set "line=!line:.wav=%NewExtension%!"
If you enable delayed expansion before assigning %%a:
@echo on & setlocal ENABLEEXTENSIONS ENABLEDELAYEDEXPANSION
set "line=%%a"
set "line=!line:.wav=%NewExtension%!"
you'll get
Special | < > ~ \ ²³ { [ ] } € $ % & / ( ) = ? chars.flac
instead of
Special | < > ~ \ ²³ { [ ] } ! " ´ ' ` üäö @ ; : € $ % & / ( ) = ? chars.flac
Edit: Delayed expansion controls when variables in a statement are expanded. The critical statement in your script is the line
set "line=%%a"
which assigns the value of the loop variable %%a to the variable line. With delayed expansion disabled the literal value of %%a is assigned, because the script interpreter cannot expand %%a at parse time. However, when you enable delayed expansion, bang-variables are expanded at execution time, so the interpreter looks at the value of %%a and expands any !whatever! in it before the result is assigned to the variable line.
Perhaps it'll become clearer with an example. If you add a line
%foo% !foo!
to the input file and define the variable in the script:
@echo on & setlocal ENABLEEXTENSIONS
set "foo=bar"
set "InFile=%~1"
...
When you enable delayed expansion after set "line=%%a" neither %foo% nor !foo! are expanded before %%a is assigned to the variable line (the interpreter doesn't see the value of %%a before execution time), so you get this output:
%foo% !foo!
When you enable delayed expansion before set "line=%%a" the interpreter will expand bang-variables before assigning the result to the variable line, so you get this output:
%foo% bar
%foo% would only be expanded at parse time, at which point the interpreter cannot see the actual value of %%a, so %foo% remains a literal %foo% here.
Further assignments like set "line=!line:.wav=%NewExtension%!" don't affect bangs or percent signs inside a variable, because expansion isn't transitive, i.e. it translates !line! to %foo% bar (or %foo% !foo!) and then stops.
You can force the expansion of (percent-)variables inside variables with the call command, though. A command call set "line=!line!" first expands to call set "line=%foo% bar" in the current context, and then call evaluates set "line=%foo% bar" in a new context where %foo% is expanded to bar as well, so the variable line is assigned the value bar bar.
Just as a side note: your code is way too complicated. You'd get the exact same results with this:
set "FileToParse=%~1"
set "OutputFile=%~2"
set "NewExtension=%~3"
for /F "usebackq tokens=* delims=" %%a in ("%FileToParse%") DO (
set "line=%%a"
@setlocal ENABLEDELAYEDEXPANSION
set "line=!line:.wav=%NewExtension%!"
echo(!line!>>"%OutputFile%"
endlocal
)
来源：https://stackoverflow.com/questions/15321730/cmd-and-exclamation-marks-part-ii