[FFmpeg-trac] #11571(undetermined:new): Unexpected shell variable overwrite with `read` and `ffmpeg`

[FFmpeg]

#11571: Unexpected shell variable overwrite with `read` and `ffmpeg`
-------------------------------------+-------------------------------------
             Reporter:  Jimmy Leung  |                    Owner:  (none)
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:
                                     |  undetermined
              Version:  7.1          |               Resolution:
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
Comment (by Jimmy Leung):

 Replying to [comment:3 MasterQuestionable]:
 > ͏    Would !`ffmpeg -i "$var"` reproduce?
 > ͏    Caveat the shell's field splitting on unquoted variables.

 To make the loop actually work, I will need to supply output file
 argument.

 So that's what I could do, changing the original `ffmpeg` command into the
 below one.

 {{{
 - ffmpeg -hide_banner -loglevel error -c copy "$folder/${_index}.mp4" -i
 $vid_item
 + ffmpeg "$folder/${_index}.mp4" -i $vid_item
 }}}

 Without stripping away banner and log, I can reproduce a long piece of
 error message obtained at the 2nd iteration of the loop (indicated by the
 label `vid at 1:`).

 {{{
 vid at 1: ttps://github.com/tsoding/musializer/assets/165283/8b9f9653-9b3d-
 4c04-9569-338fa19af071
 ffmpeg version 7.1.1 Copyright (c) 2000-2025 the FFmpeg developers
   built with Apple clang version 16.0.0 (clang-1600.0.26.6)
   configuration: --prefix=/opt/homebrew/Cellar/ffmpeg/7.1.1_1 --enable-
 shared --enable-pthreads --enable-version3 --cc=clang --host-cflags=
 --host-ldflags='-Wl,-ld_classic' --enable-ffplay --enable-gnutls --enable-
 gpl --enable-libaom --enable-libaribb24 --enable-libbluray --enable-
 libdav1d --enable-libharfbuzz --enable-libjxl --enable-libmp3lame
 --enable-libopus --enable-librav1e --enable-librist --enable-librubberband
 --enable-libsnappy --enable-libsrt --enable-libssh --enable-libsvtav1
 --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-
 libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-
 libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma
 --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-
 libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-
 libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-
 libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox
 --enable-audiotoolbox --enable-neon
   libavutil      59. 39.100 / 59. 39.100
   libavcodec     61. 19.101 / 61. 19.101
   libavformat    61.  7.100 / 61.  7.100
   libavdevice    61.  3.100 / 61.  3.100
   libavfilter    10.  4.100 / 10.  4.100
   libswscale      8.  3.100 /  8.  3.100
   libswresample   5.  3.100 /  5.  3.100
   libpostproc    58.  3.100 / 58.  3.100
 [in#0 @ 0x138632ca0] Error opening input: Protocol not found
 [in#0 @ 0x138632ca0] Did you mean
 file:ttps://github.com/tsoding/musializer/assets/165283/8b9f9653-9b3d-
 4c04-9569-338fa19af071?
 Error opening input file
 ttps://github.com/tsoding/musializer/assets/165283/8b9f9653-9b3d-
 4c04-9569-338fa19af071.
 Error opening input files: Protocol not found
 }}}

 Somehow the first few characters go missing.

 Tested it few more times. Seems it only happens to `ffmpeg`, but not
 `ffprobe` nor `grep` nor other shell utilities.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/11571#comment:5>
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