China DOS Union

Some netizens asked me for a piece of code to detect which sub - directories under a certain folder are empty. I originally thought it would be very simple to solve it with dir, but when I tested it, I found that things were not that simple. During this period, I changed several ideas, and it actually took me two hours to solve the problem. The following is my problem - solving process:

At first, I thought I could first use dir /ad /b /s to get the paths of all sub - directories, and then judge whether the sub - directory is empty by getting whether the output of "dir /a sub - directory" is empty. The code is as follows:

@echo off

setlocal enabledelayedexpansion

for /f "delims=" %%i in ('dir /ad /b /s') do (

    for /f %%j in ('dir /a /b "%%i"') do if "%%j"=="" echo "%%i" has no files

)

pause

However, no matter how I changed the environment for testing, I could never detect the empty directory. I couldn't figure out why, so I gave up the idea of detecting empty values to detect empty directories.

I changed to the following code to view test.txt and found that the result of dir for the empty directory took 9 lines (including blank lines).

@echo off

cd.>test.txt

setlocal enabledelayedexpansion

for /f "delims=" %%i in ('dir /a /b /s') do >>test.txt dir /a "%%i"

start test.txt

Then I thought of using the method of detecting the number of lines in the dir result to detect whether the folder is empty, and got the following code:

@echo off

set num=0

setlocal enabledelayedexpansion

for /f "delims=" %%i in ('dir /ad /b /s') do (

    for /f %%j in ('dir /a "%%i"') do set /a num+=1

    if!num! lss 8 echo "%%i" has no files

    set num=0

)

pause

So far, the problem has been solved.

Later, after discussing in the group, I found that the above code can also be optimized, and there are several other schemes for detecting whether the folder directory is empty, such as the rd scheme, the copy scheme. For the sake of time, the principle will not be explained too much for the time being.

[ Last edited by namejm on 2007 - 1 - 6 at 12:22 AM ]

TO namejm, the code segment 1 is detected, and the possible reasons are as follows:
for /f %%j in ('dir /a /b "%%i"') do if "%%j"=="" echo "No files under %%i"
The above statement cannot execute normally when %%i is an empty value, because 'dir /a /b "%%i"' is empty, that is, there is no %%j at all, so the desired result cannot be achieved.

When %%i is empty, it is similar to the following code.
Test statement:
for /f %i in () do if "%i"=="" (echo ok ) else echo no
When the above code is executed, nothing is displayed. Is it unexpected?

Using findstr can avoid this situation:

@echo off

setlocal enabledelayedexpansion

for /f "delims=" %%i in ('dir /ad /b /s') do (

    dir /a /b "%%i"|findstr .>nul||echo %%i

)

pause

[ Last edited by youxi01 on 2006-12-5 at 01:45 PM ]

Using findstr to detect is indeed a method. However, compared with the code in the top post, it is slightly less efficient. The problem lies in the use of the pipe symbol. In addition, the statement to enable variable delay with 2F can be removed.

Based on the statement in building 2, a more concise and efficient code is obtained:

@echo off

set flag=

for /f %%i in ('dir /a /b "Target folder"') do set flag=1

if defined flag (echo The folder is not empty) else echo This is an empty folder

pause

Thanks to the reminder from the downstairs, an error was modified.

[ Last edited by namejm on 2007-1-6 at 12:17 AM ]

There is a vulnerability in the code of floor 4. If the judgment of "target folder" does not exist is wrong. If there is only a file under "target folder", the judgment is wrong.

Hehe, there is indeed a flaw. I was too quick when writing the code and added an extra parameter d.

As for the situation where an error occurs because the "target folder" does not exist, it should not be classified as a flaw because it is to detect the target folder. The default prerequisite is that this target folder exists, which belongs to implicit declaration rather than explicit declaration. Hehe, I used a term, which is like showing off in front of Guan Gong.

Today when I was looking through old posts, I found that I once wrote a more concise code for this problem (please click here to view), I actually forgot it myself, heh, unexpected gain. After modifying a few characters, I will post it again:

@echo off

dir /a /b "target folder"|findstr .>nul&& echo has files || echo no files

pause

Some files have no file extensions...

In the findstr command, the dot is not an ordinary character but a special symbol in regular expressions, meaning any character, which has the same function as? or * in the dir command: wildcard. Files without extensions can also be processed correctly.

一般很少用findstr，还以为那个“.”是后缀的那个:P