thanks for the info, it cleared some things up, and made others foggy, its
just something i will have to clarify on my own to myself later on :)
again, thanks for the help and info
From: Alan Porter <[EMAIL PROTECTED]>
Reply-To: Triangle Linux Users Group discussion list <[email protected]>
To: Triangle Linux Users Group discussion list <[email protected]>
Subject: Re: [TriLUG] missing packages help
Date: Sun, 17 Sep 2006 14:59:37 -0400
i was trying to to show all the files that begain with lib. i was looking
to see if i could find something similar to the libobdcinst
You were trying to show all of the PACKAGES that started with "lib". You
were not trying to show all of the FILES IN THE CURRENT DIRECTORY that
started with "lib".
It's a subtle, but very important distinction. Once you figure out what
the shell is doing with what you type, things tend to make a lot more
sense.
When there are no files that begin with "lib", the shell can do one of
two things:
(1) replace "lib*" with ""
(2) keep the "lib*"
im confused about option 1)... but thats what they made man pages for, ill
have to look into that later.
The shell replaces wildcards before it calls the command. Here's some
examples.
$ ls
(expand wildcards, no wildcards, so just do "ls")
resume.pdf
song1.mp3
song2.mp3
$ ls *.mp3
(expand wildcards, so "ls song1.mp3 song2.mp3")
song1.mp3
song2.mp3
$ shopt -s nullglob ; ls *.doc
(expand wildcards, no matches, nullglob is set, so "ls ")
resume.pdf
song1.mp3
song2.mp3
$ shopt -u nullglob ; ls *.doc
(expand wildcards, no matches, nullglob is not set, so "ls *.doc")
no such file "*.doc"
This is what I meant by "Each of these may seem intuitive under different
circumstances". In this case, it seems more intuitive to leave nullglob
unset and get an error message from "ls". "ls" had no idea what to do when
it was passed "*.doc". It was looking for a file called, literally,
"star-dot-doc".
If you'd like to see a case there it's more intuitive to have nullglob set,
try "touch *.ogg" in an empty directory. What did it do? If nullglob was
set, it would create a file called "*.ogg". Not what you thought, was it?
The "touch" command simply did the best it could with what the shell told
it to do. The shell tried to expand the wildcard, failed, and passed the
wildcard on to "touch". The only thing "touch" knew how to do was create
an empty file called "star-dot-ogg".
For people who come from the DOS world, it might seem weird for the shell
to do the filename wildcard expansion. DOS programmers typically had to do
that themselves. So each DOS program tended to handle wildcard expansion a
little differently. Ugh.
An exercise for the reader... which is more conservative when using "rm
*.pdf", setting nullglob or not? This is why I leave nullglob OFF (I set
it with a "shopt -u nullglob" in my .bashrc).
Anyway, it sounds like you're on your way with the libraries. I hope this
little lesson in bash and other unix shells has not been too much of a
diversion. And I hope it sheds some light on what might otherwise seem
like unpredictable behavior.
Alan
.
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