Re: Test failure in tac (coreutils-5.92) on Solaris

[Jim Meyering]

Peter Fales <address@hidden> wrote:
> On Solaris, tac is failing when reading from stdin and stdin is a terminal.
> (it works on Linux)  E.g. a command like this works:
>
>       $ echo 'a\nb' | tac
>       b
>       a
>
> But simply running tac from the command line results in getting a shell
> prompt back (no chance to type anything):
>
>       $ tac
>       $
>
>
> The problem seems to be around line 548 in tac.c
>
>       548    file_size = lseek (fd, (off_t) 0, SEEK_END);
>       549
>       550    ok = (0 <= file_size
>       551          ? tac_seekable (fd, filename)
>       552          : tac_nonseekable (fd, filename));
>
> On linux lseeking on stdin returns -1, resulting in a call to
> tac_nonseekable.  But, on Solaris, lseek returns 0.

Thanks for the detailed report.
Here's a patch:

2005-10-24  Jim Meyering  <address@hidden>

        * src/tac.c (tac_file): When determining whether a file is seekable,
        also test whether it is a tty.  Using only the lseek-based test would
        give a false positive on Solaris.  Reported by Peter Fales.

Index: src/tac.c
===================================================================
RCS file: /fetish/cu/src/tac.c,v
retrieving revision 1.125
diff -u -p -r1.125 tac.c
--- src/tac.c   9 Sep 2005 21:11:36 -0000       1.125
+++ src/tac.c   24 Oct 2005 16:01:53 -0000
@@ -547,9 +547,9 @@ tac_file (const char *filename)
 
   file_size = lseek (fd, (off_t) 0, SEEK_END);
 
-  ok = (0 <= file_size
-       ? tac_seekable (fd, filename)
-       : tac_nonseekable (fd, filename));
+  ok = (file_size < 0 || isatty (fd)
+       ? tac_nonseekable (fd, filename)
+       : tac_seekable (fd, filename));
 
   if (!is_stdin && close (fd) != 0)
     {