Re: DRAFT: PROPOSAL: Add option 'piped-list' to read file list from stdin

[José Bollo]

On Tue, 26 Apr 2022 08:32:30 -0600
arnold@skeeve.com wrote:

> Just use xargs .... :-)

hum? how? In one case it is just the same as using $() from the shell
(but less direct). In the other case, you use -n 1 and it add one
more fork. So IMHO in both cases there is no advantages to use xargs.

> Arnold
> 
> José Bollo <jobol@nonadev.net> wrote:
> 
> > This is just an idea. Why is it not possible to get the list of
> > file from stdin? Why is it not already in grep? It seems so obvious
> > and useful that is was maybe withdrawn before (for some good
> > reason).
> >
> > I was doing a script with
> >
> >    file . [condition] -exec grep -q EXPR {} ; -print
> >
> > but it could also be written
> >
> >    file . [condition] | grep -pl EXPR
> >
> > if the proposal is accepted.
> >
> > With the two BIG advantages are:
> >   - there is only 2 processes, not 1 + the count of files
> >   - there is no need to check limit on size of arguments of a
> > command
> >
> > Here below the patch (not tested, just an idea here). More advanced 
> > usage could read from a file instead of stdin but it is of less 
> > importance IMHO.
> >
> > Best regards
> > José Bollo
> >
> > diff --git a/src/grep.c b/src/grep.c
> > index 4109ae4..98ffd84 100644
> > --- a/src/grep.c
> > +++ b/src/grep.c
> > @@ -555,6 +555,7 @@ static struct option const long_options[] =
> >     {"version", no_argument, NULL, 'V'},
> >     {"with-filename", no_argument, NULL, 'H'},
> >     {"word-regexp", no_argument, NULL, 'w'},
> > +  {"piped-list", no_argument, NULL, 'p'},
> >     {0, 0, 0, 0}
> >   };
> >
> > @@ -1089,6 +1090,7 @@ static intmax_t max_count;    /* Max
> > number of selected lines from an input file.  */
> >   static bool line_buffered;        /* Use line buffering.  */
> >   static char *label = NULL;      /* Fake filename for stdin */
> > +static bool piped_list;         /* Read file list from stdin */
> >
> >
> >   /* Internal variables to keep track of byte count, context, etc.
> > */ @@ -2000,6 +2002,7 @@ Pattern selection and interpretation:\n"), 
> > getprogname ());
> >         printf (_("\
> >   \n\
> >   Miscellaneous:\n\
> > +  -p, --piped-list          get file list from stdin\n\
> >     -s, --no-messages         suppress error messages\n\
> >     -v, --invert-match        select non-matching lines\n\
> >     -V, --version             display version information and
> > exit\n\ @@ -2698,6 +2701,10 @@ main (int argc, char **argv)
> >           only_matching = true;
> >           break;
> >
> > +      case 'p':
> > +   piped_list = true;
> > +        break;
> > +
> >         case 'q':
> >           exit_on_match = true;
> >           exit_failure = 0;
> > @@ -2986,27 +2993,49 @@ main (int argc, char **argv)
> >     if (fts_options & FTS_LOGICAL && devices ==
> >   READ_COMMAND_LINE_DEVICES) devices = READ_DEVICES;
> >
> > -  char *const *files;
> > -  if (0 < num_operands)
> > -    {
> > -      files = argv + optind;
> > -    }
> > -  else if (directories == RECURSE_DIRECTORIES && 0 <
> > last_recursive)
> > +  bool status = true;
> > +  if (piped_list)
> >       {
> > -      static char *const cwd_only[] = { (char *) ".", NULL };
> > -      files = cwd_only;
> > -      omit_dot_slash = true;
> > +      size_t size = 0;
> > +      char *file = NULL;
> > +      ssize_t rsize;
> > +      out_file = true;
> > +      while ((rsize = readline(&file, &size, stdin)) > 0)
> > +        {
> > +     if(file[rsize - 1] == '\n')
> > +       {
> > +         file[--rsize] = 0;
> > +       }
> > +          if (rsize > 0)
> > +       {
> > +         status &= grep_command_line_arg (file);
> > +       }
> > +   }
> > +      free(file);
> >       }
> >     else
> >       {
> > -      static char *const stdin_only[] = { (char *) "-", NULL };
> > -      files = stdin_only;
> > -    }
> > +      char *const *files;
> > +      if (0 < num_operands)
> > +        {
> > +          files = argv + optind;
> > +        }
> > +      else if (directories == RECURSE_DIRECTORIES && 0 <
> >   last_recursive)
> > +        {
> > +          static char *const cwd_only[] = { (char *) ".", NULL };
> > +          files = cwd_only;
> > +          omit_dot_slash = true;
> > +        }
> > +      else
> > +        {
> > +          static char *const stdin_only[] = { (char *) "-", NULL };
> > +          files = stdin_only;
> > +        }
> >
> > -  bool status = true;
> > -  do
> > -    status &= grep_command_line_arg (*files++);
> > -  while (*files != NULL);
> > +      do
> > +        status &= grep_command_line_arg (*files++);
> > +      while (*files != NULL);
> > +    }
> >
> >     return errseen ? EXIT_TROUBLE : status;
> >   }
> >
> >
> >