can I use a variable to extract a substring in batch?

Question

I need to extract the characters of a string one by one in a loop. Ideally, I would've done something like this, but as you might have guessed, it doesn't work.

@echo off
setlocal EnableDelayedExpansion
set /a len=5
set var=abcde
for /l %%n in (1,1,%len%) do (
    set /a num=%%n - 1
    echo %var:~!num!,1%
)

it works seamlessly if I replace !num! with a plain number, but with the variable, behaves as if the percent signs aren't there and echoes:

var:~0,1
var:~1,1
var:~2,1
var:~3,1
var:~4,1

https://stackoverflow.com/questions/10166386/arrays-linked-lists-and-other-data-structures-in-cmd-exe-batch-script/10167990#10167990 — Aacini, Jul 12 '20 at 10:48

Gerhard · Accepted Answer · 2020-07-11T19:21:47.730

3

To directly fix your issue replace:

echo %var:~!num!,1%

with:

call echo %%var:~!num!,1%%`

But you can do it without set /a num=%%n - 1 because you are already counting using for /L but note we are counting from 0.

Also note, we start couting from 0.
@echo off
setlocal EnableDelayedExpansion
set /a len=4
set "var=abcde"
for /l %%n in (0,1,%len%) do (
    echo(!var:~%%n,1!
)

edited Jul 11 '20 at 19:21

answered Jul 11 '20 at 17:07

Gerhard

22,678
7
27
43

your example code works perfectly fine for echoing, but I'd like to write it to a variable. echoing it was mainly for troubleshooting. My bad, I should've said that in the question. – Stian Mykland Jul 12 '20 at 14:09
I got it to work with a little bit of tweaking. Thanks for the help – Stian Mykland Jul 12 '20 at 14:26
Well, show you want to write it and I can show you how. – Gerhard Jul 12 '20 at 14:37

can I use a variable to extract a substring in batch?

1 Answers1