UNIX challenge of the day

Why did I just run this command (as root):

# cat ~tai/jukebox-2.19b.pl >/usr/bin/jukebox.pl

instead of this one:

# cp ~tai/jukebox-2.19b.pl /usr/bin/jukebox.pl

?

I promise you, there is a good reason. :-)

--
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In article <bv4tv2-6rs.ln1@ophelia.g5n.co.uk>, usenet200509
@tobyinkster.co.uk says...
> Why did I just run this command (as root):
>
> # cat ~tai/jukebox-2.19b.pl >/usr/bin/jukebox.pl
>
> instead of this one:
>
> # cp ~tai/jukebox-2.19b.pl /usr/bin/jukebox.pl
>
> ?
>
> I promise you, there is a good reason. :-)
>
>
you haven't sobered up from last night yet?

On Sat, 17 Sep 2005 10:41:31 +0100, Toby Inkster
<usenet200509@tobyinkster.co.uk> wrote:

¶Why did I just run this command (as root):
¶
¶ # cat ~tai/jukebox-2.19b.pl >/usr/bin/jukebox.pl
¶
¶instead of this one:
¶
¶ # cp ~tai/jukebox-2.19b.pl /usr/bin/jukebox.pl
¶
¶?
¶
¶I promise you, there is a good reason. :-)
¶
¶--

Er, because the pubs are shut? because there's nothing on TV? Because
you like posting messages to the wrong Usenet group?

Am I warm?

Matt


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On Sat, 17 Sep 2005 1012 GMT, DoobieDo <dave@bytext.co.uk> wrote:

¶In article <bv4tv2-6rs.ln1@ophelia.g5n.co.uk>, usenet200509
¶@tobyinkster.co.uk says...
¶> Why did I just run this command (as root):
¶>
¶> # cat ~tai/jukebox-2.19b.pl >/usr/bin/jukebox.pl
¶>
¶> instead of this one:
¶>
¶> # cp ~tai/jukebox-2.19b.pl /usr/bin/jukebox.pl
¶>
¶> ?
¶>
¶> I promise you, there is a good reason. :-)
¶>
¶>
¶you haven't sobered up from last night yet?

LOL!

I hadn't thought of that one!

Matt


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__/ [Toby Inkster] on Saturday 17 September 2005 10:41 \__

> Why did I just run this command (as root):
>
> # cat ~tai/jukebox-2.19b.pl >/usr/bin/jukebox.pl
>
> instead of this one:
>
> # cp ~tai/jukebox-2.19b.pl /usr/bin/jukebox.pl
>
> ?
>
> I promise you, there is a good reason. :-)

Because it looks more original?

Now truly, it seems like it would achieve the same, although at an
underlying level the machine will handle it differently (not sure to what
extent either). I am trying to think along the lines of overwrite,
recursive copying or even that past story of yours about executive rm -rf
..* as root.

Roy

--
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2:10pm up 23 days 2:24, 2 users, load average: 2.52, 1.17, 0.78

Roy Schestowitz wrote:
> __/ [Toby Inkster] on Saturday 17 September 2005 10:41 \__
>
>
>>Why did I just run this command (as root):
>>
>># cat ~tai/jukebox-2.19b.pl >/usr/bin/jukebox.pl
>>
>>instead of this one:
>>
>># cp ~tai/jukebox-2.19b.pl /usr/bin/jukebox.pl
>>
>>?
>>
>>I promise you, there is a good reason. :-)
>
>
> Because it looks more original?
>
> Now truly, it seems like it would achieve the same,

No it wouldn't.

The first commandline pipes the output of cp to jukebox.pl and there *is* no
output from the cp command - so it would create an empty file. The second
commandline actually copies the file.

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In: <bv4tv2-6rs.ln1@ophelia.g5n.co.uk>, Toby Inkster <usenet200509@tobyinkster.co.uk> wrote:
>Why did I just run this command (as root):
>
> # cat ~tai/jukebox-2.19b.pl >/usr/bin/jukebox.pl
>
>instead of this one:
>
> # cp ~tai/jukebox-2.19b.pl /usr/bin/jukebox.pl
>
>?
>
>I promise you, there is a good reason. :-)

Oh goody! a unix question! :-)

I can think of a few, generally having to do with timestamps
and/or the file descriptors.

Thats supposedly how one might trim a log:

$ cat /dev/null >log

Or:

$ >log

If another process had 'jukebox.pl' open, and you copied the file,
the opened process might use a different file descriptor pointing
to a file that no longer exists.

Or:

You don't have permission to write to /usr/bin but you do
have write permission to /usr/bin/jukebox.pl ?

The '#' would indicate you have root permission, but some filesystems
have extended attributes and/or network filesystems where even root
doesn't have such access.

Or:

Is jukebox.pl a symlink?

Or:

You want to clobber the data in the original file so it can't be
recovered as easily?

Or:

jukebox.pl is a named pipe used to talk to a daemon process.


Those are the reasons off the top of my head, there are probably other
reasons, probably relating to the directory entry or an open file handle.

Now, here's my question to you, if it's not a named pipe, why transfer
data from tia's home directory to /usr/bin? instead of /usr/local/bin ?
Is 'jukebox.pl' a package from the operating system vendor?

If it is a named pipe, why have it in /usr/bin ?

Jamie
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