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

[arnold]

Just 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 useful that is was maybe withdrawn before (for some good reason).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;
>   }
>
>
>