[bunny-Giles]

Hi,

I am a beginner with batch scripting and would be grateful for some advice...

Is it possible to use a for loop within a for loop in a batch script? - I need to loop through 1000 files and for each file repeat a 3 second cycle up to 300 times

To that end, how do I break out of the second for loop early?

Also, can you explain how delayed expansion works - i've seen it in scripts, but don't get what it does...would I need it here?

Any help will be gratefully received.
Thanks

[jahwi]

You can use a for loop within a for loop. This is called a nested loop. You can type this:

Code

FOR /?

In an open command prompt window to get the full list of switches and uses.
Also, you should get a standard batch programming PDF to get you started.
As for exiting the loop early, That ranges between implausible and impossible.

When you're online, go here: Tutorial to learn batch scripting from this forum.

Welcome to batch.

[ɩᴄᴀʀᴜȿ ᴌוᴠᴇѕ™]

Code

for . . . (. . .) do (
    for . . . (. . .) do (
        if . . . equ . . .  (
            do something
        )
    )
)

[b00st3d]

This is something I put together a while ago to demonstrate what delayed expansion does.

Code

@echo off
setlocal enabledelayedexpansion
set x=1
echo +=========================================+
echo ^| No delayedexpansion ^|^| delayedexpansion ^|
echo ^|=========================================^|


REM Batch parses a for loop as soon as it reaches the loop by default
REM this results in the variables that are in the loop not being updated x in this case
REM Although the end result is the same if you need to interact with x during the loop
REM then you will need to enable delayed expansion.

REM delayedexpansion causes batch to parse the value of the variable every time it comes across
REM the variable.  In a loop this means the variable can be change it's value through the loop.
REM run this script to see the example below.


for /l %%a in (1,1,8) DO echo ^|      x = %x%          ^|^|       x = !x!      ^|& set /a x=x+1
echo ^|=========================================^|
echo ^|      x = %x%          ^|^|       x = !x!      ^|
echo +=========================================+
pause >nul

[annikk.exe]

Hi,

I am a beginner with batch scripting and would be grateful for some advice...

Welcome! ::purr::
You have found a good place here. Lots of friendly people/cats to play and learn with. :>

Is it possible to use a for loop within a for loop in a batch script?

Yes it is! Although, there are a couple of different methods...

- I need to loop through 1000 files and for each file repeat a 3 second cycle up to 300 times

Are all of the files in the same folder?
If that's the case, you can get the list of 1000 files using dir /b /a:-d
(Dirbad is actually the name of a pirate, true story..)

The /b bit means "use basic formatting"
The /a:-d part is for selecting "attributes" of the files we want, in this case, we want only files that are NOT directories (hence "-d" instead of "d")

Try typing dir /b /a:-d at a command prompt so you can see what this command does. :>

Then you need to loop over the files...
So I would suggest to use a for /f loop to iterate over each entry in the dir /b /a:-d output.
Since we don't want the loop to split the line up into tokens, we should also specify that there are no delimiters.

Code

for /f "delims=" %%a in ('dir /b /a:-d') do (
  echo Oki now I am processing %%a
)

Are you following along so far? :> This is the outer part of the loop. We can cover the inner part too, but let you know if you have any questions about this so far.. :>

To that end, how do I break out of the second for loop early?

Spoiler alert... we use a GOTO statement. :P

Also, can you explain how delayed expansion works - i've seen it in scripts, but don't get what it does...would I need it here?

You might need it here, depending on how you choose to do your loops.

Okay... here goes my Delayed Expansion explanation.
In batch, normally we refer to variables like %variable%
If we enable Delayed Expansion, we can also refer to that same thing as !variable!

The exclamation marks are a different set of symbols, which also denote a variable.

Example:

Code

@echo off
setlocal EnableDelayedExpansion

set "var=Cats are best"

echo %var%
echo !var!
pause

Code

Cats are best
Cats are best
Press any key to continue . . .

Okay, so hopefully this gets you comfortable with the idea that !variable! == %variable%

Now, the question is, what does this let you do?
Well, the difference comes with the way the variables are evaluated.

The crux is that percentages are evaluated when the interpreter reaches that line
whereas exclamations are evaluated when the interpreter reaches the variable

So for example, when we run a line of code like this:

Code

echo %var%
echo !var!

First batch evaluates any percentage-variables to their actual values, and the line becomes this:

Code

echo Cats are best
echo !var!

So that is why it's called "Delayed Expansion"
Because exclamation variables are not evaluated when the line is reached.. their evaluation is "delayed" until the last possible moment. :>


Delayed Expansion is very useful for creating array-like behaviour, or for iterating over characters in a string, and for a number of other advanced things.

Any help will be gratefully received.
Thanks

And likewise, we will fall all over ourselves to help you out, when you show the slightest interest in learning.. :> ::purr::

[Zystem Fryar]

Learn to use :Labels,
learn to Call them,
learn to end sections with goto :EOF
and learn to break out of them when you need to with the same...

[bunny-Giles]

Thank you for all your responses:
Particular thanks to annikk.exe for the detailed break down; b00st3d for the helpful demonstration and jahwi for pointing me to the tutorial.

[ɩᴄᴀʀᴜȿ ᴌוᴠᴇѕ™]

https://hackforums.net/showthread.php?tid=3645708

[Zystem Fryar]

https://hackforums.net/showthread.php?tid=3645708

Good one :)
Nearly got all my tricks in there :)

[ɩᴄᴀʀᴜȿ ᴌוᴠᴇѕ™]

Good one :)
Nearly got all my tricks in there :)

Could you clarify on "your" tricks?

[Zystem Fryar]

Could you clarify on "your" tricks?

Well, within batch, Some specifics with how I handle Tokens, and their expansion. and assigning them to variables before a call statement (to avoid shifts in the Label)

example:

Code

FOR /F "tokens=1-14 delims=;" %%a IN ("CtrlLine_.lst")  DO  set vr1_a=%%a &&  set vr1_b=%%b &&  set vr1_c=%%c &&  set vr1_d=%%d &&  set  vr1_e=%%e &&  set vr1_f=%%f &&  set vr1_g=%%g &&  set vr1_h=%%h &&  set vr1_i=%%i &&  set vr1_j=%%j &&  set vr1_k=%%k &&  set vr1_l=%%l &&  set vr1_m=%%m &&  set vr1_n=%%n && call :Label ....

or in some cases

Code

FOR /F "tokens=1-14 delims=;" %%a IN ("CtrlLine_.lst")  DO  (
  set vr1_a=%%a
  set vr1_b=%%b
  set vr1_c=%%c
  set vr1_d=%%d
  set vr1_e=%%e
  set vr1_f=%%f
  set vr1_g=%%g
  set vr1_h=%%h
  set vr1_i=%%i
  set vr1_j=%%j
  set vr1_k=%%k
  set vr1_l=%%l
  set vr1_m=%%m
  set vr1_n=%%n
  call :Label ....
)

[ɩᴄᴀʀᴜȿ ᴌוᴠᴇѕ™]

Well, within batch, Some specifics with how I handle Tokens, and their expansion. and assigning them to variables before a call statement (to avoid shifts in the Label)

example:

Code

FOR /F "tokens=1-14 delims=;" %%a IN ("CtrlLine_.lst")  DO  set vr1_a=%%a &&  set vr1_b=%%b &&  set vr1_c=%%c &&  set vr1_d=%%d &&  set  vr1_e=%%e &&  set vr1_f=%%f &&  set vr1_g=%%g &&  set vr1_h=%%h &&  set vr1_i=%%i &&  set vr1_j=%%j &&  set vr1_k=%%k &&  set vr1_l=%%l &&  set vr1_m=%%m &&  set vr1_n=%%n && call :Label ....

or in some cases

Code

FOR /F "tokens=1-14 delims=;" %%a IN ("CtrlLine_.lst")  DO  (
  set vr1_a=%%a
  set vr1_b=%%b
  set vr1_c=%%c
  set vr1_d=%%d
  set vr1_e=%%e
  set vr1_f=%%f
  set vr1_g=%%g
  set vr1_h=%%h
  set vr1_i=%%i
  set vr1_j=%%j
  set vr1_k=%%k
  set vr1_l=%%l
  set vr1_m=%%m
  set vr1_n=%%n
  call :Label ....
)

Along with the improper use of '&&', it still doesn't explain the difference between how these are YOUR tricks, and just the syntax of the language.

[jahwi]

Along with the improper use of '&&', it still doesn't explain the difference between how these are YOUR tricks, and just the syntax of the language.

...more stuff about Icarus going after Zystem...

Remember that the OP is a FOR-loop beginner. Stop posting code snippets that the OP does not understand. @Icarus good one tho.