Notes - UNIX I

Wednesday, June 03, 1998
Reviewed: finger, who, date, cal

Last Updated: Monday, June 08, 1998 at 3:15 PM

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Lefthand refers to The Waite Group's UNIX Primer Plus - Sams.
Primer refers to UNIX In A Nutshell - O'Reilly & Associates.
Mastering the Shell refers to UNIX Applications Programming: Mastering the Shell - Sams.
Secrets refers to UNIX Secrets - IDG Books.

Communicating With Other Users

Command:
talk cn6

61, 325-326, 440 (Primer)
2-104 (Lefthand)

[CTRL-C] generally cancles command in progress. To end a command that is waiting on keyboard input, type [CTRL-D].

If talk isn't possible (due to configuration differences), write can be used for dialog, (though this technique is quit cumbersome and even annoying at times):

Command:
write cn6

429(Primer)
2-121 (Lefthand)
295 (Secrets)

write cn6[ENTER]

Type message here.[CTRL-D]

This message brought to you by Dr. G:
A FILE is a STREAM O' BYTES!! Live it, love it, learn it!!

Command:
mesg [y,n]

325-326, 440(Primer)
2-72 (Lefthand)

mesg n: Makes yourself not available for talk/write (receiving or sending). Can also use: mesg no.
mesg y: Makes yourself available for talk/write (receiving or sending). Can also use: mesg yes.

Command:
wall

2-119 (Lefthand)

wall[RETURN]

Type message here.[CTRL-D]

Will send message to ALL users logged in at the time.

Command:
pine

327, 329-341, 344, 358-360 (Secrets)

First, there was mail, then elm . Then there was pine, which stands for "pine is not elm". (According to its developers, PINE stands for "Program for Internet News and E-mail")

System Status

pwd - print working directory
cd /etc[RETURN] - change directory (to /etc)
cd[RETURN] - change directory to home dir

df - shows space available in the user's file system.
du - show disk utilization in the user's file system.

stty - changes the way the terminal interacts with the UNIX system.

To set the backspace key to erase, type the following:
stty erase ^H (hit backspace key to make ^H)
Until we learn later how to modify our account, this step must be taken every session on clyde.

The easiest way to make a plan: create a file named .plan that contains your plan.
Example:
cat > .plan Type your plan here. Hit [CTRL-D] to exit/save.

You can finger anyone (connected by network, Internet, etc.) if you know their name & server.

File Structure

The "inverted tree" depicting file structure as designed by Dennis Ritchey for MULTIC that was carried over to UNIX.

Real operating systems use a right slash [/], while others use a left slash [\].
root starts every file system. There can be multiple file structures on one device as well as one file structure on multiple devices.

File structure is simply a way to address locations on devices.
cd var/adm[RETURN]
(A space must be placed between cd and parameter. UNIX is "whitespace delimited" (whitespace: one or more tabs or spaces)).

Command:
ls

75-79, 437-438 (Primer)
2-67 (Lefthand)
41-42, 115-118 (Mastering the Shell)
35-36, 38, 43, 82-88, 93,
104-111, 123-124, 133, 135-136,
241, 296, 302, 455 (Secrets)

Used to list the contents of a directory.

75-79, 437-438 (Primer)
2-67 (Lefthand)
41-42, 115-118 (Mastering the Shell)

ls -l: Long format listing (includes permissions, owners, size, modification time, etc.)
ls -a: List all files, including the normally hidden . files.

ls -i: List the inode for each file.

Permissions:
3 types of permissions: r (read), w (write), x (execute)
3 levels of permission: user, group, other
Each level of permission has 3 possible types of permissions:

**drwxr-xr--**
d File/Dir	rwx User	r-x User's Group	r-- Other
d = directory	r = able to read to this file/dir w = able to write this file/dir x = able to execute this file	r = able to read to this file/dir w = permission denied x = able to execute this file	r = able to read to this file/dir w = permission denied x = permission denied

Be careful to make only truly executable files. UNIX will try to run all executable files designated as so!

The rest of the colums using ls -l are:

# of links that file has
who owns the file
size of file
date and time (or year, if more than one year old)
OR last time file was accessed
actual filename

Directories are always multiples of 512 (which is the classical size of directories).

Files are broken into blocks.

Command:
ls -la
UNIX doesn't have extensions. You can use 255 characters for a file name. A period is just another character, except when the 1st character of a filename, when it "hides" the file. These files are called "dotted" files.

This message brought to you by Dr. G:
Dotted files are exempt from file matching metacharacter expansion. Live it, love it, learn it!!

Command:
touch

75-79, 437-438 (Primer)
2-67 (Lefthand)
41-42, 115-118 (Mastering the Shell)

Can be used to create an empty file.
Can be used to update time last access of existing files.

(make is used to create large compiled things - it will compile anything younger tahn a certain date - can force make to compile a file by touching that file, causing it to fall in the "compilable" date, thus being recompiled.)

2-70, 19-2 (Lefthand)
250, 648 (Secrets)

Command:
history

2-70, 19-2 (Lefthand)
272-276, 279-280, 425, 447(Primer)

A numbered list of previous commands and provides a shorthand notation letting you repeat or modify previous commands (-per Primer, pg. 425).

Command:
mkdir

90, 200-201, 438-439 (Primer)
2-91 (Lefthand)
130, 295 (Secrets)

-r Allows file readibility.
-w Allows file write-ability (can change contents of fileand erase-ability!).
-r Allows file executability (can use file matching metacharacters into directory). [What the hell does that mean??]

Command:
rmdir

90, 200-201, 438-439 (Primer)
2-91 (Lefthand)
130, 295 (Secrets)

Remove directory. Clyde is configured to promt before removing a directory!

Command:
rmdir -r

90, 200-201, 438-439 (Primer)
2-91 (Lefthand)
130, 295 (Secrets)

Recursive removal. On Clyde, will expand directory and prompt user to enter "y" or "n" in asking if the user wishes to remove for each file/dir. Be careful! Some systems aren't configured to prompt first! Try to use rm -r as little as possible.

All file structures have two special directories:
. This means "here - this directory where I am now".
.. This means "go up one level in directory heirarchy".

../../.. Means "move up three levels in heirarchy".

Command:
cp

196, 202-206, 213, 437(Primer)
2-19 (Lefthand)
128-129 (Secrets)

Copy. (Notice this OS doesn't print "1 file copied" after making a copy of a file. It assumes you actually know what you are doing. Imagine that!)

Command:
cat Ferengi.Rules

79-81, 85-87, 436 (Primer)
2-10 (Lefthand)
42-44 (Mastering the Shell)
114-116, 122, 139 (Secrets)

Concatenates and displays file (Ferengi.Rules).

Command:
more

75-79, 437-438 (Primer)
2-7382-83, 438 (Lefthand)
114-116 (Secrets)

displays file content with --MORE-- option (allowing easier reading).
[SPACEBAR] -Scrolls down one page at a time.
[ENTER] -Scrolls down one line at a time.
q -Quit

Command:
less

759-760 (Secrets)

displays file content with --MORE-- option (allowing easier reading).
less is more -only backwards!!

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