Questions[cat](ubuntu)

The simplest way to display file contents is using the cat command:

cat file.txt

I can get the same result using input redirection:

cat < file.txt

Then, what is the difference between them?

From a given a file, I have a requirement to create a copy that is padded with zeros to a specific size.

If you create a file with the following.

echo test >testfile

The output of the following command is inconsistent.

cat testfile /dev/zero | dd bs=256k count=1 status=none | od -c

This is the output that I would expect.

0000000   t   e   s   t  \n  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
0000020  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
*
1000000

But you also randomly get either of the following.

0000000   t   e   s   t  \n
0000005

0000000   t   e   s   t  \n  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
0000020  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
*
0400000  \0  \0  \0  \0  \0
0400005

Why does this command have inconsistent behavior?

Even if dd is cutting the pipe off at the end of the first file, The 128k result is strange. I get the same inconsistent results under 16.04, 18.04 and 19.04 systems.

I have several videos in a folder;

~/Downloads/movie1.mkv
~/Downloads/movie2.mkv
~/Downloads/movie3.mkv

I would like to extract the bitrate for each file, and output the data into a single text file, or output list which I can copy and paste into a text file.

I have installed ffmpeg.
So, for example, the output of ffmpeg -i movie1.mkv is;

Metadata:
    encoder         : libebml v1.2.0 + libmatroska v1.1.0
    creation_time   : 2011-04-09T18:18:05.000000Z
  Duration: 00:04:27.71, start: 0.000000, bitrate: 10698 kb/s
    Stream #0:0(eng): Video: h264 (High), yuv420p(progressive), 1920x1038, SAR 1:1 DAR 320:173, 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)
    Metadata:
      title           : movie1
    Stream #0:1(eng): Audio: dts (DTS), 48000 Hz, 5.1(side), fltp, 1536 kb/s (default)
    Metadata:
      title           : DTS-ES 5.1 @ 1509 Kbps
    Stream #0:2(eng): Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s
    Metadata:
      title           : Commentary
    Stream #0:3(eng): Subtitle: subrip
    Stream #0:4(eng): Subtitle: subrip

The "bitrate: 10698 kb/s" is the crucial part I am after here.
Let's pretend all three movies have the same bitrate.

I would like to extract the bitrate information from all three videos, and have them output as;

movie1.mkv 10698
movie2.mkv 10698
movie3.mkv 10698

How would I go about extracting and outputing this information in bulk?

I've been trying a combination of finding by file name, ffmpeg, and then | to grep. e.g ; find . -name "*.mkv" -exec ffmpeg -i "${1%.mkv}" | grep "bitrate:"

Current attempts;

1. The command

   ffmpeg -i movie1.mkv 2>&1 | grep bitrate | sed 's/bitrate: \(.*\), kb/\1/g'
   

   returns

   Duration: 00:04:27.71, start: 0.000000, bitrate: 10698 kb/s

2. The command

   find . -name "*.mkv" -exec ffprobe -v error -show_entries format=bit_rate -of default=noprint_wrappers=1:nokey=1 "${~/Downloads/1%.mkv}"  ';`'
   

   returns

   ~/Downloads/1%.mkv: No such file or directory ~/Downloads/1%.mkv: No such file or directory ~/Downloads/1%.mkv: No such file or directory

I feel that I'm close here, and that there's just something wrong with the find and recalling the output of find into ffprobe.

i am trying to read an odt file from terminal. When i type cat myfile.odt it shows me an image like this

As the question says, I need to edit my /proc/acpi/wakeup file, but when I open it with any text editor, it shows blank file. cat command, on the other hand, displays correct file contents in terminal. When I navigate to that file in file manager, it says it's size is 0 bytes. I'm using Xubuntu 15.04. I'm thoroughly confused.