Re: grep . /; echo $?

[Charles Levert]

* On Monday 2005-10-24 at 15:58:30 +0100, Julian Foad wrote:
> Dan Jacobson wrote:
> >$ grep . /;echo $?
> >1
> >$ strace grep . /
> >...open("/", O_RDONLY|O_LARGEFILE) = 3
> >fstat64(3, {st_mode=S_IFDIR|0755, st_size=1024, ...}) = 0
> >read(3, 0x8071000, 32768) = -1 EISDIR (Is a directory)...
> 
> For comparison, here is how it handles other problems with reading the
> files:
> 
> >$ grep . @; echo $?
> >grep: @: No such file or directory
> >2

According to the grep(1p) POSIX "man page":

]  EXIT STATUS
]         The following exit values shall be returned:
]  
]          0     One or more lines were selected.
]          1     No lines were selected.
]         >1     An error occurred.
]  
]  CONSEQUENCES OF ERRORS
]         If the -q option is specified, the exit status
]         shall be zero if an input line is selected,
]         even if an error was detected.

This does not restrict GNU grep from being more
informative about what happened by documenting
and using many exit statuses that are greater
than 1 (e.g., open() error vs. read() error),
using either successive values (2, 3, 4, 5, ...)
or bit flags (2, 4, 8, ...).


> On the other hand, I wonder whether this behaviour was intentional.  The
> "info" help text says slightly more than the "man" page:
> 
> >`--directories=ACTION'
> >     If an input file is a directory, use ACTION to process it.  By
> >     default, ACTION is `read', which means that directories are read
> >     just as if they were ordinary files (some operating systems and
> >     filesystems disallow this, and will cause `grep' to print error
> >     messages for every directory or silently skip them).
> 
> I don't know: it all seems a bit arbitrary and inconsistent.  What's the
> point of defaulting to ACTION="read" on systems that don't support it?

Consistency (for grep) across OSes.  If OSes
are inconsistent, that is another issue; grep
should merely use its exit status to document
what actually happened at a lower level on the
OS on which it happens to be running.