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DOS batch managing blank lines (CRLF) using for

Posted on 2015-02-04
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Last Modified: 2015-02-04
I am trying to create a copy of a text file by changing a single specific line that matches a pattern.  I wrote the batch script below which works fine except it creates the output without the blank lines (CRLF) in the original. I tried to explicitly echo blank lines with code like if "x!line!"=="x" echo.>>output.txt to no avail.

for /f "tokens=* delims=" %%s in ('type input.txt ^| find /v "" ') do (
	set line=%%s
	
	if "!line:~0,21!"=="specific_pattern"	(
		echo this_new_line_instead>> output.txt
	) else (
		echo !line!>> output.txt
	)

)

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How to preserve the blank lines in the original file?
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Question by:TAI-
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3 Comments
 
LVL 85

Accepted Solution

by:
oBdA earned 500 total points
ID: 40588303
for /f just skips over empty lines, and never enters the loop body.
You can do a workaround by telling find.exe to add the line number, and then strip the line number right off again:
@echo off
setlocal enabledelayedexpansion
set InFile=input.txt
set OutFile=output.txt
for /f "tokens=1* delims=]" %%s in ('type "%InFile%" ^| find.exe /n /v "" ') do (
	set line=%%t
	if "!line:~0,21!"=="specific_pattern"	(
		>>"%OutFile%" echo.this_new_line_instead
	) else (
		>>"%OutFile%" echo.!line!
	)
)

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Expert Comment

by:DrAtomic
ID: 40588327
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Author Closing Comment

by:TAI-
ID: 40588703
Works perfect.

While searching how to do this I actually saw examples of using the /n parameter for find. But as luck would have it they were examples where the line numbers were actually used so it never occured to me to just strip them.
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