CODEWITHSUNDEEP
windowsffmpeggnuplotstdin
DDS
DDS

Reputation: 2478

Gnuplot how to set a variable to standard-input if not passed

I have a gnuplot script (plot.script) that is invoked like

C:> ffmpeg -i '.\my_awesome_audio_file.wav' -filter_complex aformat=channel_layouts=mono -acodec pcm_s16le -ar 4000 -f data - | gnuplot -e "fileout='plot';fileformat='png';wid=500;" .\plot.script

Now I'd want to default filein variable to stdin if it is not passed as argument. This because I want to be able to call this script as a 1-liner command with ffmpeg data generation and also as step-by-step procedure

My idea was to use

if(!exists('filein')){
filein = '-';
}

but this throws warning: Skipping data file with no valid points

if i print the variable datafile I got - (I expected something like stdin).

this is the plot.script script:


if(!exists('filein')){
    filein = '-';
    }

if (!exists("hei")){
    hei = 4444;
    }
if (!exists("wid")){
    wid = 5555;
    }
if(!exists("fileformat")){
     fileformat = 'png';
     }
if(!exists("fileout")){
     fileout = 'risultato';
   }
   
fileout = fileout . '.' . fileformat;
   
if(!exists("dataformat")){
    dataformat = '%int16';
    }
if(fileformat eq 'png'){
  set terminal png transparent size larghezza,altezza;
  
  }else{
  set terminal fileformat size wid,hei;
  }
  set output fileout;
  unset key;
  unset tics;
  unset border;
  set lmargin 0;
  set rmargin 0;
  set tmargin 0;
  set bmargin 0;


print filein;
plot filein binary filetype=bin format=dataformat endian=little array=1:0 with lines linecolor "0x009900";

But I also want to call this command-by-command: generate the data-file:

c:> ffmpeg -i '.\my_awesome_audio_file.wav' -filter_complex aformat=channel_layouts=mono -acodec pcm_s16le -ar 4000 -f data audio.dat

plot the data:

c:> gnuplot -e "filein='audio.dat';fileout='plot';fileformat='png';wid=500;" .\plot.script

Upvotes: 0

Views: 238

Answers (1)

Ethan
Ethan

Reputation: 15118

There are probably a lot of ways you might deal with this, but my suggestion is to have gnuplot plot from a pipe opened by the shell command that calls it. It is then up to the shell to fill that pipe either via cat from an existing file or by directing a stream to it. Here is the relevant section from the documentation (see help pipes)

 On systems with an fdopen() function, data can be read from an arbitrary file
 descriptor attached to either a file or pipe.  To read from file descriptor
 `n` use `'<&n'`.  This allows you to easily pipe in several data files in a
 single call from a POSIX shell:

       $ gnuplot -p -e "plot '<&3', '<&4'" 3<data-3 4<data-4
       $ ./gnuplot 5< <(myprogram -with -options)
       gnuplot> plot '<&5'

Upvotes: 0

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