DOS truncated string ~

@ Echo off

Set STR = 123456789

The first character of ECHO is: % STR :~ 0, 1%
The echo header contains two characters: % STR :~ 0, 2%
The first five characters of ECHO are: % STR :~ 0, 5%
The echo string after removing the last character is: % STR :~ 0,-1%.
The string after removing the last 3 Characters in ECHO is: % STR :~ 0,-3%.
Echo 4th characters: % STR :~ 3, 1%
The echo 4th and later 3 characters are: % STR :~ 3,4%
The last echo character is: % STR :~ -1%
The last echo character is: % STR :~ -1,1%
The last echo character is: % STR :~ -1,2%
Echo countdown 4th characters: % STR :~ -4,1%
The last 4th and subsequent characters of ECHO are: % STR :~ -4%
The last 4th echo characters and the following 1 character are: % STR :~ -4,2%
The last 4th echo characters and the following two characters are: % STR :~ -4,3%

Pause

In order to illustrate this problem, I will take the batch processing characters here for further explanation, hoping to inspire new users.

As follows:


Echo % var :~ N, K %


Here we will explain each parameter: "% Var", that is, the string from which we want to intercept characters ."~ "Take words
Mark (I understand this), "N" is understood as a pointer, and "K" is understood as an offset address.
: The pointer and offset address are both from scratch)

We still use the namejm moderator's example to describe:
@ Echo off
Set STR = 123456789

Rem defines a STR string as 123456789
The first character of ECHO is: % STR :~ 0, 1%
The REM pointer is 0 and the offset address is 1, that is, starting from 0th bits and taking 1 bits

The echo header contains two characters: % STR :~ 0, 2%

The REM pointer is 0 and the offset address is 2, that is, starting from 0th bits and taking 2 bits

The first five characters of ECHO are: % STR :~ 0, 5%

Rem

The pointer is 0, and the offset address is 5, that is, starting from 0th bits and taking 5 bits

The echo string after removing the last character is: % STR :~ 0,-1%.

When "K" is a negative value, we can understand as follows: from the beginning of the pointer, take all the characters after it, and then subtract

Next, "ABS (k) bit"... so this sentence can be interpreted as follows: Get all its characters from the first byte

Is: 123456789 and then subtract the ABS (k) bit from the back, so the final result is: 12345678

The string after removing the last 3 Characters in ECHO is: % STR :~ 0,-3%.

Rem
This sentence is the same as above.

The last echo character is: % STR :~ -1%

Rem
Both the "N," and "K" parameters are default values. The default value is "N," which can be understood as: Get all the values starting from the ABS (k) bit.

The last 4th and subsequent characters of ECHO are: % STR :~ -4%

Rem
Same as above

The last echo character is: % STR :~ -1,1%

Rem
When N is a negative value, it indicates that the characters are truncated from the back and k characters are taken (at this time, N should start from 1)

The last echo character is: % STR :~ -1,2%

Rem
Same as above

Echo countdown 4th characters: % STR :~ -4,1%

Rem
Same as above

The last 4th echo characters and the following 1 character are: % STR :~ -4,2%

Rem
Same as above

The last 4th echo characters and the following two characters are: % STR :~ -4,3%

Rem interpretation is the same as above.

pause