Re: Cat a directory

From: Mark Terribile (materribile_at_yahoo.com)
Date: 09/22/03

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To: freebsd-questions@freebsd.org, Karlsson Mikael HKI/SOSV <mikael.karlsson@hel.fi>

    I hesitate to step into the fray; it appears that
    the phrase `more heat than light' now applies. But
    ...

    >> Says who? cat works fine on binary files. The
    >> problem you are having is that people are using
    >> cat to *display* files. "Fixing" that problem
    >> could break cat for its more standard use: ...

    (One of my favorite bugs: the key-bug: ``If the
    complex
    hyperbolic arctan2 routine didn't give the wrong
    answer
    for arguments of ( -1, -1 ), ( -1, -1 ) the operating
    system scheduler would lock up.'')

    > ... my problem is people using cat on directories.

    Is your problem that people use cat on directories,
    or that your purpose is to cater to people who, for
    want of training that you are yet to give them,
    don't know not to use cat on directories?

    > Try to run for example "cat /bin" in Linux, HP-UX,
    > Solaris and other *NIXes and I'm 90% certain that
    > they will not show the directory but an error
    > message ... But then FreeBSD spits out crap ...

    One program's crap is the file system's meat.

    My recollection, which I cannot test at the moment,
    is that on at least some of those OS's it is the OS
    itself which refuses to allow cat(1) to open the file,
    giving an EISDIR on the attempt. One could argue
    that Linux found it necessary to do so because Linux
    supports so many file system types that you couldn't
    interpret the directory contents anyway; they all have
    different internal structures; and that this indicates
    that Linux is, in this area, more advanced. It's
    certainly a plausible argument--when applied to this
    part of the OS's interface. (Aside to the BSD team:
    does the Linux personality module get this right?)

    > ... which I can't see the point of ever using
    > anywhere even when piping a tube up your ass!

    Why do we call it blue language when it is in the
    deep infrared? It really looks bad in print; let's
    please just avoid it.

    > But since newbies do this frequently it shouldn't
    > be possible to do so.

    If you're providing the accounts to them, then put
    the appropriate alias in their .profile or .login
    files, or add a path component pointing to a nubi-bin.
    When they take off the training wheels, they can
    remove the alias or the path component. Until then
    their safety is your concern.

    If someone else is providing the accounts, perhaps
    the someone else is open to suggestions, especially
    if they also have to deal with this problem?

    >>> and why is this already done to less and not cat?
    >> less is made to display files. It's the correct
    >> tool for the job.
    > And you mean that cat is built to show directories
    > ... Man I must of mised that in school ... right?

    Please, this is something about which reasonable
    people can disagree. Linus and his team obviously
    disagree with the FreeBSD team; I think they are all
    reasonable people, even though I sometimes disagree
    with one or another of them. There, you see: several
    proofs-by-example.

    [Ruben de Groot]
    >> So why don't you for example alias cat to cat -v
    >> in your system profile ...

    > So it's better for a newbie to get understandable
    > jibrish from cat when run on directories then an
    > error message stating that they are trying to run
    > cat on a directory ...

    The case CAN be made both ways. If these are CS
    majors, they probably should get used to learning
    by picking up clues from their environment; that's
    how most programs are debugged and they have to learn
    the skills. If they are admins-in-training, the case
    is even stronger. So long as the terminal doesn't
    lock up, this is a good chance for them to develop
    trained curiousity. On the other hand, if you are
    serving accounting majors or paralegals, they would
    probably be better served by the error message.
    (Race car drivers and taxicab drivers go to different
    schools, except in NYCity and Boston.)

    It's easy to write a script that runs file(1) on the
    targets and cat(1)s those when the output includes
    "[tT]ext" but puts a message on &2 (standard error)
    otherwise. Install that as an alias, or in a path
    component, and the job is done, probably in less
    time than we've spent writing these essays.

    Now think about having to do that on a non-UNIX OS.
    It might be very hard. It might even be impossible.

    > ... And while we're on the subject... why doesn't
    > ls support coloring of different file types like
    > in Linux. As it would make finding certain files
    > easier by coloring them differently depending on
    > their ending.

    Well, I think it's the file type, not the suffix, that
    determines the color, but my only concern is to shut
    the frotzenglarken color off whenever I meet a Linux
    system, since it makes it harder for me to read the
    screen rapidly. I don't deprive all users of it, I
    just free myself from it.

    You see, reasonable people can disagree. Unreasonable
    people argue, fume, fulminate and fester. And yes,
    from time to time I get unreasonable, too. Not that
    I'm proud of it. It's putting immediate satisfaction
    ahead of reaching my goals. And it looks really bad
    in print.

                                  Mark Terribile
     === The pattern matches in this code work in ===
     === ksh and bash, but not in /bin/sh . Note ===
     === the absolute pathname. ---MaT ===
    #!/usr/local/bin/ksh

    for safecat_arg in ${@} ; do
            safecat_ftype="$(file "${safecat_arg}")"
            if [[ $safecat_ftype = *text* ]] ; then
                    /bin/cat "${safecat_arg}"
            else
                    echo >&2 "${safecat_ftype}"
            fi
    done

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