Extract Part of a text file in BAT - batch-file

Question

I am capturing a m3U file on a daily basis but wish to parse part of it to another file with the few channels I need.
For example I have renamed my m3U to Test.txt file which say has the following fictional structure:
#EXTINF:0,ABC
#live link 1
#EXTINF:0,XYZ
#live link 2
#EXTINF:0,UVW
#live link 3
I would just like to capture say the line staring from "#EXTINF:0,XYZ" and say the line beneath it to end up with a Output.txt as follows:
#EXTINF:0,XYZ
#live link 2
I know that one needs to use the For loop but I am a bit of a noob on this area.

Answer 1

Put this code into the file filter.cmd.
#echo off
set INPUT=%1&set MATCH=%2& set MATCHED=0
for /f "delims=" %%a in (%INPUT%) do call :line "%%~a"
goto :eof
:line
set EXT=&TITLE=&
for /f "tokens=1 delims=:" %%a in ("%~1") do set EXT=%%~a
for /f "tokens=1,2,* delims=:," %%a in ("%~1") do set TITLE=%%~c
if "%EXT%" == "#EXTM3U" echo %~1
if "%EXT%" == "#EXTINF" (
set MATCHED=0
echo %TITLE%| findstr /l %MATCH% >nul && set MATCHED=1
)
if %MATCHED%==1 echo %~1
Use example:
filter.cmd input_file.m3u XYZ > output_file.m3u
Here is some explanation:
Every input line is split using for /f with tokens and delims.
MATCHED is set if the line begins with #EXTINF and the rest contains the string to match (second argument).
if MATCHED is set, the lines are output until next #EXTINF.

Answer 2

I would do it like this, supposing the .m3u file does not contain trailing white-spaces in the lines preceded by #EXTINF, like your sample data does:
#echo off
setlocal EnableExtensions DisableDelayedExpansion
rem // Define constants here:
set "FILE=%~1"
set "HEADER=#EXTM3U"
set "PREFIX=#EXTINF"
set "MATCH=%~2"
set "FLAG="
for /F usebackq^ delims^=^ eol^= %%L in ("%FILE%") do (
if defined FLAG (
echo(%%L
set "FLAG="
)
for /F "delims=:" %%P in ("%%L") do (
if "%%P"=="%HEADER%" (
echo(%%L
) else if "%%P"=="%PREFIX%" (
set "LINE=%%L"
setlocal EnableDelayedExpansion
if /I "!LINE:*,=!"=="!MATCH!" (
echo(!LINE!
endlocal
set "FLAG=#"
) else endlocal
)
)
)
endlocal
exit /B
Call the script like this, supposing it is saved as extract-entry.bat:
extract-entry.bat "input_file.m3u" "XYZ" > "output_file.m3u"
The script walks through the given .m3u file line by line. It returns the current line unedited and resets variable FLAG, if variable FLAG is set, which is not the case at the beginning.
Then it looks for #EXTINF. If found (e. g., #EXTINF:0,XYZ), the string after the comma (XYZ) is compared against the given search string. If matched, the current line is output and FLAG variable is set now in order to get the following line too.
The header line #EXTM3U is always output.
Toggling delayed expansion makes this script robust against all characters that have special meaning to the command interpreter without losing them.