批处理bat命令读取当前文件夹下每个文件的第一行

思路：读取当前文件夹下文件名单并保存到txt，设置flag标识行数，两层循环读取文件内容

@echo off & setlocal enabledelayedexpansion //关闭所有命令回显，启动变量延迟（用!!括起变量）

dir */b >filenamesThisDir.txt //保存当前目录下文件名到txt，覆盖原内容

set lineFlag=0
set OUTPUT_FILE=outputcsv.csv

if exist %OUTPUT_FILE% del %OUTPUT_FILE%

for /f "usebackq delims=*" %%i in ("filenamesThisDir.txt") do ( //注意双引号单引号的使用，参考/?
    set /a lineFlag+=1 // ‘/a'支持计算
    if !lineFlag! GEQ 0 ( //greater equal
        set lineContent=%%i
        echo lineContent= !lineContent!

        set lineflag2=0
        for /f "usebackq delims=*" %%j in ("!lineContent!") do (
            set /a lineflag2+=1
            if !lineflag2! ==1 (
                set lineC2=%%j
                echo lineC2 = !lineC2!
                echo !lineC2! >>%OUTPUT_FILE% //将读取内容保存到目标文件，接续在文件尾
            )
        )

    )
)

参考：
https://bbs.csdn.net/topics/392078603
https://blog.csdn.net/greenery/article/details/17146431
https://blog.csdn.net/i_likechard/article/details/79984294
https://blog.csdn.net/wsq119/article/details/116303559
http://www.bathome.net/thread-41717-1-1.html
https://baike.baidu.com/item/BAT/365230#6-8
https://blog.csdn.net/gqg_guan/article/details/123200677
https://blog.csdn.net/chuangxin/article/details/104100725
https://blog.csdn.net/HYK_DJ5201314/article/details/127985459
https://www.zhihu.com/question/587211918
https://zhuanlan.zhihu.com/p/54572985
https://www.cnblogs.com/xpwi/p/9628613.html
https://www.cnblogs.com/wengzhijie/p/11428155.html
https://www.cnblogs.com/zwk-It-goodmorning/p/14204844.html