UNIX for Dummies Questions & Answers

Hello,
I am currently interning at a place and my job is to essentially learn UNIX. My supervisor gives me problems here and there to help guide me with my learning but for the most part I'm doing this all by self-teaching myself. Needless to say I have run into a few obstacles...for instance

-Create a *one* line command that, using tar, will collect the full /usr/local directory (you need to run this as root again) and copy the whole /usr/local structure under /opt
For example /usr/local/bin/hello will become /opt/local/bin/hello, etc.

I want this as follows:
1. /usr/local is collected by tar, but the output of this tar command is its stdout.
2. what you get from the previous stdout, you compress with gzip and send it to stdout again
3. get this output and decompress with gzip.
4. get this output and pipe to tar in a way that will extract the tree under /opt.

If anyone knows how I could go about doing this, please let me know, or at the very least point me in the right direction. What I've got so far (which could be completely wrong) is:

tar cvf - usr/local/ | gzip -c - | gunzip -c - | tar xvf -

in theory I feel like this should work (except for extracting the tree under /opt...i'm kinda stuck there) So if anyone knows or has a solution it would be greatly appreciated! and maybe help me out by explaining what is involve and maybe where I went wrong.

Thanks

You're nearly there. Just use the -C /opt/ option for the last tar, to chdir into /opt before extraction. You might also want -C /opt in the first tar, so it doesn't add the whole path(you'd get usr/local/file instead of local/file out) You might also want to add the 'p' option to both tars to more strictly preserve permissions.

What is the point of the compression, though? If you're not storing it on disk inbetween creation and extraction, there's no disk space to save, making compression nothing but a waste of CPU time.

Really though the best way is to try it. Get yourself a shell and make some folders with a little junk in them and try and tar stuff back and forth until you get it working good enough to test for real.

Haha, damn I was close...if only I looked at the man page a little closer.

And ye, I asked my supervisor why he wanted to compress then decompress right away and he admitted that it is silly and useless right now but he said we'd be expanding on it later and doing stuff with it...not sure what but we'll see...haha.

and I am most definitely fooling around with junk directories and folders i've created to mess around and test things.

---------- Post updated at 02:43 PM ---------- Previous update was at 02:40 PM ----------

k so I'm getting a few errors...
when I type:
tar cvf - usr/local/ | gzip -c - | gunzip -c - | tar xvfC - /opt/

I get:
usr/local/
usr/local/bin/
usr/local/bin/hello/
usr/local/
tar: usr/local: Cannot mkdir: No such file or directory
usr/local/bin/
tar: usr/local/bin: Cannot mkdir: No such file or directory
usr/local/bin/hello/
tar: usr/local/bin/hello: Cannot mkdir: No such file or directory
tar: Exiting with failure status due to previous errors


I'm sure I've just got the wrong syntax or something but I keep messing around with it and I keep getting errors.

Thanks

It's trying to extract it in /opt/ which won't work unless you're root. And if you're still testing don't do it as root! Stick in your home dir and test in there.

Your parameters don't look quite right.

Code:

tar cvf - usr/local/ | gzip -c - | gunzip -c - | tar -C opt/ -xvf -

By doing 'opt/' instead of '/opt/' you can test in an opt dir inside your current dir instead of stomping over /opt/ itself.

Oh I see now!
haha thanks, makes a lot more sense then what I had.

Thanks a bunch!

tar is very old, like dd and a few others, before UNIX command structure gelled, and it writes a lot of nulls because it wants your tape records to be standard length. If you do not have tape records, use cpio, which is what scp -r and rcp -r use and which has a pass option. Once, I updated a whole subtree in Hong Kong from Nj over 56K WAN using:

(cd source; find ...|cpio ...)|gzip -9 | rsh remote_host "cd target;gunzip | cpio -u ..."

exact options vary. This is very like 'scp -Crp ....' I like the -c for control strings in characters (compress better and platform independent). Be careful of all the *cp -r options, as if the target already exists and is a dir, it puts source things beneath it, but if not, it creates it, so you tend to accidentally get dir1/dir1/..., easily fixed with a move, but just remember some *cp -r commands are not repeatable.

Aight, I'm starting to see where my supervisor is going with the compressing and decompressing bit. I believe it's to compress the file then transfer through ssh and then uncompress on another machine. If I wanted to get a head start on that where should I start?
am I going to be using scp?
or is there a way for me to use "...| tar -C opt/" and replace the opt/ and refer to the directory of the local machine I am transfering the files to?