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DOS批处理 & 脚本技术（批处理室） » [Discussion] Question about character extraction

Floor1　lzbow	Posted 2010-04-28 15:22
初级用户　Posts 13　Credits 23
Please look at this @echo off echo set123456789>123.txt set b=123456789 echo %b:~0,5% >>123.txt echo %b:~-5% >>123.txt echo %b:~2,5% >>123.txt echo %b:~-5,3% >>123.txt echo %b:~-5,-4% >>123.txt echo %b:~-5,-3% >>123.txt Why is it that echo %b:~0,5% >>123.txt echo %b:~-5% >>123.txt echo %b:~2,5% >>123.txt echo %b:~-5,3% >>123.txt directly display what they extract, but echo %b:~-5,-4% >>123.txt echo %b:~-5,-3% >>123.txt display what remains after their extraction?

Floor2　Hanyeguxing	Posted 2010-04-28 17:44
银牌会员　Posts 897　Credits 1,039　From 在地狱中仰望天堂
set123456789 12345 56789 34567 567 5 56 The result is like this? That's perfectly normal. I can't see what the problem is.

Floor3　Hanyeguxing	Posted 2010-04-29 17:35
银牌会员　Posts 897　Credits 1,039　From 在地狱中仰望天堂
About "string extraction": %a:~]% 　　The square brackets indicate optional parts, % is the variable identifier, a is the variable name and cannot be omitted, the colon is used to separate the variable name and the description part, and the symbol ～ can simply be understood as "offset". m is the offset (default is 0, meaning extraction starts from the 1st character), and n is the extraction length (default is all). %a:~0,n% takes the leftmost n characters %a:~-m% takes the rightmost m characters %a:~m,n% takes n characters starting from position m+1 %a:~m,-n% starts from position m+1, up to the (n+1)th character from the end %a:~m % takes everything to the right starting from position m+1.