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Hello friends

set k=1 & set j=20 && for /l %1 in (%k%,1,%j%) do @echo %1

Output:
0 ---> zero

why is zero above command output?

Please guide me in this regard .

In a batch try this:


Read that last post too.

Because of how batch expands variables, the %k% and %j% are not set when the for loop is executed.

When a for /L loop tries to use an variable that has no value, it treats it like 0 instead, so your code is getting translated to which outputs 0 and then stops.

Put the for loop on a separate line; && is used when you only want the right side to run if the left side runs successfully, and a simple set statement will not fail.

Also, %1 through %9 are traditionally used for parameters that get passed in to scripts; you can use them for for loop variables, but it's better to use letters instead.

I am going to assume you are trying to do this with one line from the cmd prompt.

There is no need to enter your commands in one line!

You either enter it with your known values already in place, (as in the first window)…

…or enter it on three lines, (as in the lower window) Takes no more key presses!

Or you could do in 2 lines:

This would work if the DOS window had been started with delayed environment variable expansion enabled.
See CMD /? for details which include

CMD /? wrote:

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Delayed environment variable expansion is NOT enabled by default.  
You can enable or disable delayed environment variable expansion for a
particular invocation of CMD.EXE with the /V:ON or /V:OFF switch.

One practical way of doing this is to create a shortcut to the DOS Prompt on your Desktop and change the Target: line in Shortcut Properties to
John A.

thefeduke wrote:This would work if the DOS window had been started with delayed environment variable expansion enabled.
...
John A.

This will do the trick:

hacker wrote:set k=1 & set j=20 && for /l %1 in (%k%,1,%j%) do @echo %1

Output:
0 ---> zero

why is zero above command output?

The reason is that CMD only sets the variable at the end of a line. Run this script and you will see how that occurs.

ShadowThief wrote:When a for /L loop tries to use an variable that has no value, it treats it like 0 instead, so your code is getting translated to

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for /l %1 in (0,1,0) do @echo %1

which outputs 0 and then stops.

Well, this is not entirely exact... This result is the combination of two factors:

- In a FOR /L command, if anyone of the "start,step,end" values is NOT a number, then it is taken as a zero value. For example: "for /L %i in (NOTNUM,1,10) do ..." would loop with values from 0 to 10 because the part "NOTNUM" is NOT a number (independently if a variable named NOTNUM may exist).

- In the command line, if a variable enclosed in percents-signs does NOT exist, then its name and the percent-signs are NOT changed. This way, in this particular example: "for /l %1 in (%k%,1,%j%) do @echo %1" the "%k%" and "%j%" parts are NOT replaced, so the values of "start" and "end" are "%k%" and "%j%" respectively, that are taken as zero because they are NOT numbers. If this FOR would be executed in a Batch file, then the "%k%" and "%j%" parts would be just removed and the FOR would not be executed at all.

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I think the simplest way to execute this FOR from the command-line is this way:


... but this method only works the first time, when both "k" and "j" variables does not exists. This means that it would be necessary to delete "k" and "j" variables in order to execute the FOR again with different values.

Antonio

I agree with Aacini.
You could add a ^ to delay the expansion, so that the for loop always uses actual k,j values.
But then the variables ^k and ^j needs to be undefined, or defined as %k% or %j%.
(If prefer not using such variable names - but you cannot be sure if using foreign code.)


penpen

I changed this reply as I missed reading ShadowThief's comments well enough.

Aacini wrote:I think the simplest way to execute this FOR from the command-line is this way:

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set k=1 & set j=20 & cmd /C for /l %i in (%k%,1,%j%) do @echo %i

... but this method only works the first time, when both "k" and "j" variables does not exists. This means that it would be necessary to delete "k" and "j" variables in order to execute the FOR again with different values.

Antonio

In my testing it works every time Antonio, but I expect you meant that changing the variables causes a little hiccup.

It does work when changing the variables in my test too, but it has to be run twice and on the second time it returns the correct changed values.