[FFmpeg-devel] [PATCH] Make the ffmpeg "Overwrite ? [y/N]" question work with more than one file to overwrite

[Stefano Sabatini]

On date Saturday 2009-03-14 10:59:56 +0100, Stefano Sabatini encoded:
> On date Friday 2009-03-13 18:32:40 -0700, Baptiste Coudurier encoded:
> > On 3/13/2009 6:30 PM, Michael Niedermayer wrote:
> > > On Sat, Mar 14, 2009 at 01:14:13AM +0100, Stefano Sabatini wrote:
> > >> On date Wednesday 2009-03-11 01:42:10 +0100, Michael Niedermayer encoded:
> > >>> On Tue, Mar 10, 2009 at 09:36:00PM +0100, Stefano Sabatini wrote:
> > >>>> Hi all,
> > >>>>
> > >>>> I recently stepped into this:
> > >>>> stefano at geppetto ~/s/ffmpeg> ffmpeg -i in123.mpeg out0.avi out1.ogg -y -map 0:2 -map 0:1
> > >>>> [...]
> > >>>> Input #0, mpeg, from 'in123.mpeg':
> > >>>>   Duration: 00:03:40.05, start: 0.500000, bitrate: 81 kb/s
> > >>>>     Stream #0.0[0x1c0]: Audio: mp2, 48000 Hz, stereo, s16, 64 kb/s
> > >>>>     Stream #0.1[0x1c1]: Audio: mp2, 48000 Hz, stereo, s16, 64 kb/s
> > >>>>     Stream #0.2[0x1c2]: Audio: mp2, 48000 Hz, stereo, s16, 64 kb/s
> > >>>> File 'out0.avi' already exists. Overwrite ? [y/N] y   
> > >>>> File 'out1.ogg' already exists. Overwrite ? [y/N]
> > >>>> Not overwriting - exiting
> > >>>>
> > >>>> After the first question is replied, the stdin buffer still contains
> > >>>> the '\n' buffered, then ffmpeg read from it with getchar(), get a
> > >>>> '\n', which is different from 'Y' and abort immediately.
> > >>>>
> > >>>> Patch fixes it.
> > >>>>
> > >>>> Regards.
> > >>>> -- 
> > >>>> FFmpeg = Fast and Faboulous Most Picky Energized Gorilla
> > >>>> Index: ffmpeg.c
> > >>>> ===================================================================
> > >>>> --- ffmpeg.c	(revision 17926)
> > >>>> +++ ffmpeg.c	(working copy)
> > >>>> @@ -3362,12 +3362,13 @@
> > >>>>               filename[1] == ':' ||
> > >>>>               av_strstart(filename, "file:", NULL))) {
> > >>>>              if (url_exist(filename)) {
> > >>>> -                int c;
> > >>>> +                char c, line[256];
> > >>>>  
> > >>>>                  if (!using_stdin) {
> > >>>>                      fprintf(stderr,"File '%s' already exists. Overwrite ? [y/N] ", filename);
> > >>>>                      fflush(stderr);
> > >>>> -                    c = getchar();
> > >>>> +                    fgets(line, sizeof(line), stdin);
> > >>>> +                    sscanf(line, "%c", &c);
> > >>> what weird mess is this ?
> > >>> getchar();getchar()
> > >> underkill, what if the user prints more than one character?
> > > 
> > > if the user enters more than 2 chars to a question asking for one
> > > then interpreting this as 'y' is maybe not such a good idea.
> 
> This is the behaviour of many programs which reads yes/no repyies from
> stdin, in particular I refer to the coreutils.
> 
> But we can easily change this, and force the user to provide any
> case-insensitive substring of "yes" for example.
> 
> > > also, from a user POV, just having to press y and no enter would be nice
> 
> That's potentially dangerous, IMO is safer to let the user *explicitely*
> press enter to confirm.
> 
> > > 
> > 
> > Weee termcap :>
> > Don't forget mingw though.
> 
> Anyway if we decide that this is a good idea, we can extend read_yes()
> to support that.
> 
> Regards.
> -- 
> FFmpeg = Frightening & Fiendish Mastodontic Pitiful Enigmatic Gymnast

> Index: cmdutils.h
> ===================================================================
> --- cmdutils.h	(revision 17951)
> +++ cmdutils.h	(working copy)
> @@ -152,4 +152,10 @@
>   */
>  void show_formats(void);
>  
> +/**
> + * Returns a positive value if reads a line starting with [yY] from
> + * standard input, 0 otherwise.
> + */
> +int read_yes(void);
> +
>  #endif /* FFMPEG_CMDUTILS_H */
> Index: cmdutils.c
> ===================================================================
> --- cmdutils.c	(revision 17951)
> +++ cmdutils.c	(working copy)
> @@ -472,3 +472,16 @@
>  "decoder corresponds to the h263 and h263p encoders, for file formats it is even\n"
>  "worse.\n");
>  }
> +
> +int read_yes(void)
> +{
> +    int yes;
> +
> +    /* Test against "^[yY]" */
> +    int c = getchar();
> +    yes = (c == 'y' || c == 'Y');
> +    while (c != '\n' && c != EOF)
> +        c = getchar();
> +
> +    return yes;
> +}

> Index: ffmpeg.c
> ===================================================================
> --- ffmpeg.c	(revision 17951)
> +++ ffmpeg.c	(working copy)
> @@ -3389,13 +3389,10 @@
>               filename[1] == ':' ||
>               av_strstart(filename, "file:", NULL))) {
>              if (url_exist(filename)) {
> -                int c;
> -
>                  if (!using_stdin) {
>                      fprintf(stderr,"File '%s' already exists. Overwrite ? [y/N] ", filename);
>                      fflush(stderr);
> -                    c = getchar();
> -                    if (toupper(c) != 'Y') {
> +                    if (!read_yes()) {
>                          fprintf(stderr, "Not overwriting - exiting\n");
>                          av_exit(1);
>                      }

Ping?

The function read_yes() I think is potentially useful in other
contexts, anyway if you prefer since it's used just one time I can 
add the two lines:
    while (c != '\n' && c != EOF)
        c = getchar();

directly to the current code in ffmpeg.c

Regards.
-- 
FFmpeg = Furious and Frightening Magical Philosofic Exxagerate Guru