how to replace one line in text file without removing empty lines in batch

i am trying to code a simple script in batch that can find and replace a line

so far, I've found a snippet that works perfectly fine for my purpose the only problem is that it removes empty lines and i can't figure out why!!

I've tried to add another if statement in this for loop but I fail also I found that there is a bat called JREPL, i tried to run few simple commands from the docs and i failed again XD

here is the snippet:

:Variables
set InputFile=t.txt
set OutputFile=t-new.txt
set _strFind= old "data"
set _strInsert= new "data";

:Replace
>"%OutputFile%" (
  for /f "usebackq delims=" %%A in ("%InputFile%") do (
    if "%%A" equ "%_strFind%" (echo %_strInsert%) else (echo %%A)
  )
)

i was expecting that this snippet won't remove my empty lines and i can't figure out why

Solution

I am posting this without testing, as I do not have the environment to test as we speak. But to explain your issue, cmd will ommit empty lines as it is built that way. It is the same as setting a variable to nothing and expecting it to return a result, so we simply assign values to each line by sort of simulating a detection of line breaks (Don't know exactly how to explain that one) but nevertheless, we will add some additional characters to the lines to ensure we get line breaks, the just get rid of them once we have them, So here goes:

@echo off
setlocal enabledelayedexpansion

set inputfile=t.txt
set outputfile=t-new.txt
set _strfind=old "data"
set _strinsert=new "data";
for /f "tokens=*" %%a in ('type "%inputfile%" ^| find /v /n "" ^& break ^> "%inputfile%"') do (
    set "str=%%a"
    set "str=!str:*]=!"
    if "!str!"=="%_strfind%" set "str=%_strinsert%"
    >>%outputfile% echo(!str!
)

That should send to output file.. You can however make the output file the same as the input as it would then be the same as replacing the text inline in the original file. Once I am able to test, I will fix the answer if there are any issues with it.

As a side note, be careful of where you have additional whitespace in your variables you set. For instance:

set a = b

has 2 issues, the variable, containing a space after a will be created with the space. So it will be seen as:

%a %

The aftermath of this is that the value of the variable will start with a leading space, so when you expected b as the value, it in fact became b

Then lastly, it is alsways a good idea to enclose your variables with double quotes, simply again to eliminate whitespace, because:

 set a=b

Even though you cannot see it with your naked eyes, contains a space at the end, so doing a direct match like:

if "b"=="b"

Will result in a false statement as in fact we have:

if "b"=="b "

So the correct statement would be to set variables as:

set "a=b"
if "%a%"=="b"

which will be a perfect match.

Note I posted this from my phone, so any spelling, grammar and code issues I will resolved as I go though my answer.