Question

Q:

I've spent a decade stuffing the find, grep, awk, and sed syntax into the tips of my fingers. Steadfast and faithful, I like the shell; I feel a communion with the ancients in the necropsy of a diff. But how do I open a file from the command line? Of course I understand that I can invoke an application by name, but I concede that the Tracker's preferred app intelligence is greater than my $PATH. I want the Tracker to open the file for me. How?

-- Mabel Stanley, Penzance, England

Answer 1

A:

Wander not, Mabel. The short answer: Type

/system/Tracker filename

at the command line prompt and your file will open. But, you object, that's a lot to type and hard-coded pathnames make you queasy? And when your tiny alabaster fingers slip while typing ".alias" such that you open the non-existent ".alais" instead, the Tracker doesn't object to your wrong tree up-barking, but bounds slobberingly to the front gate with no slippers in its mouth? And, what's more, you are an orphan? Then try spoon feeding the app roster.

The little app shown below, which we'll call "open", calls on the app roster to open the files that are passed as command line arguments. The heart of the code is the Launch() call; Launch() finds and launches the preferred app for each file. This works fine for files, but it doesn't work for directories, so we catch the directories that are passed in and open them with Tracker (i.e. a directory is opened as a Tracker folder window). The code is small; you can fit the entire thing in your mouth:

#include <Roster.h>
#include <Application.h>
#include <signal.h>

int main(int argc, char **argv)
{
  int n;
  entry_ref ref;
  BEntry entry;
  status_t err;
  char *arv[1];
  BApplication("application/x-open");

  if (argc == 1) {
    printf("Usage: open <file1> <file2> <file3> ...\n");
    return -1;
  }

  signal(SIGINT, SIG_IGN);

  for (n = 1; n < argc; n++) {
    get_ref_for_path(argv[n], &ref);
    entry.SetTo(&ref, false);

    if (entry.IsDirectory()) {
      arv[0] = strdup(argv[n]);
      err = be_roster->Launch("application/x-vnd.Be-TRAK",
        1, arv);
      free(arv[0]);
    }
    else
      err=be_roster->Launch(&ref);

    if (err != B_OK && err != B_ALREADY_RUNNING)
      printf("open: %s\n", strerror(err));
  }
  return 0;
}

The only line that needs an explanation is the signal() call:

#include <signal.h>
...
  signal(SIGINT, SIG_IGN);

This tells open to ignore Control+C. We don't actually care that the signal affects open itself, but we do care about how a Control+C from the command line affects an app that's launched with open. For the launched app inherits open's stdio descriptors and signal handlers, and thus it is that Control+C will kill the launched app if we don't tell the handler to ignore it.

When you launch open, it does its thing and then dies—you don't have to heave it into the shell background (i.e. you don't have to "$ open file &"). However, you should use FileTypes to set open to be a "Background App". This will prevent open from (briefly) appearing as an icon in the DeskBar. You should also set it to be "Multiple Launch", just in case (of something that isn't worth describing).

How is open different from invoking /system/Tracker? Error handling, mainly. If you try to open a non-existent file (or a file that doesn't want to be opened for whatever reason), open will tell you about it. And for the scopophiliac, "open" lets you see the normally-suppressed printf() messages that are generated by the launched app. Fun you betcha sam.

Issue 3-33, August 19, 1998

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