1. Basic UNIX
OLC Training

2. Shells
A shell is how you primarily act with the operating system at the command line
Two main types of shells:
Bourne shell & C shell
Modern variants are Bourne Again Shell (bash) and trusted c shell (tcsh)
Athena uses tcsh; most everything will be in tcsh syntax. If bash is different, it will be noted

3. Commands Most UNIX commands are of the form: command -option argument
Options (occasionally called 'flags') change the behavior of a command are usually preceded with one or two dashes
Arguments are the “input” to the command
Commands can take anywhere from 0 to n arguments and options.

4. Example Command with no options or arguments athena% renew
Command with 2 arguments and no options
athena% attach consult cref
Command with one option and no arguments:
athena% znol -l

5. Shell & Environment Variables
Contain information about working environment
Change behavior of various programs
Change behavior of shell
Environment variables apply to your login session
Shell variables apply to one instance of your shell (ie: an xterm or gnome-terminal)

6. Environment Variables
Display all environment variables:
printenv
Display a single variable
printenv USER
echo $USER
Set a variable
Tcsh: setenv FOO bar
Bash: export FOO=bar

7. Shell variables Display all variables: set Display a single variable:
echo $prompt
Set a variable:
Tcsh: set foo=bar
Bash: foo=bar

8. I/O Redirection Command > filename
Redirect output of command to new file “filename”
Command >> filename
Append output of command to new file “filename”
command < filename
read input from file called “filename”
command | command2
take the output of command and make it the input of command 2

9. Examples ls > /tmp/files.txt ls Public >>/tmp/files.txt
ls | more
sort < /tmp/files.txt

10. Basic Commands Move file1 into the directory directoryname
mv file1 directoryname
Copy file1 to the directory directoryname
cp file1 directoryname
Go back/up one level
cd ..
Create the directory directoryname
mkdir directoryname
Restore the previously deleted file file1
undelete file1
Mark file1 for deletion, will be deleted in 3 days
delete file1
Move (rename) file1 to a new file called file2
mv file1 file2
Copy file1 to a new file called file2
cp file1 file2
Change current directory to directoryname
cd directoryname
Show name of current directory
pwd
List contents of current directory ls

11. Other Commands Display contents of a file cat filename.txt
Count lines in a file:
wc -l filename.txt
(-c for characters)
Display only the beginning or end of a file
head filename.txt
tail filename.txt

12. grep grep is a “searching” utility
it matches patterns (“regular expressions”)
Can do lots of complex things, but simple text search is the best
grep dog animals.txt
ls | grep thesis
grep -i causes it to be case-insensitive

13. sort Sorts the input and displays it sort -n will sort numerically
otherwise it goes 1, 10, 2, 3, 34, 4, etc.

14. Pagers A pager allows you see one “page” of information at a time
Common pagers are “more” and “less”
Basic pager commands:
space = page down
enter = line down
b = page up
y = line up
/ = search
q = quit

15. Examples
ls | more
less mydocument.txt

16. Shell Wildcards * Match anywhere from 0 to n characters ?
match one character
Examples:
ls foo* will list “foo”, “foo2”, “foobar”
ls foo? will only list “foo2”

17. Manual Pages man commandname whatis commandname
apropos <search term>
Some commands don't have man pages (ie: fs)
Try -help, --help, -?, -h
Google

18. File Permissions
ls -l shows file permissions -rw jdreed mit 684 Sep 12 09:51 /tmp/tkt_p16901
10 columns. First is – if it's a file, “d” if it's a directory
Remaining 9 are 3 groups of 3. First group for user (u), 2nd group for group (g), 3rd group for “everyone else” (o)

19. File modes r = read (or list files, if directory)
w = write (or delete/create if directory)
x = execute (or access if directory)
s = run as though you were the owner
t = sticky (on directory, regardless of permissions files can only be accessed by the owner or root)

20. chmod change the mode of a file: chmod go-rwx myfile
remove read write and execute for group and other
chmod u+w myfile
Give yourself (owner) ability to write to file
On AFS, only the user (u) permissions are used, group and other are ignored, as they are governed by AFS permissions

21. Jobs and Processes ps show processes in current shell ps -u
show all your processes
ps ax (or ps -ef)
show all processes on the machine

22. Foreground and Background
All processes are run in the foreground by default
ie: you start xcluster, you don't get your athena prompt back until it's done
Add an & to the end of the command to run in the background
To background an already running process
Ctrl-Z to suspend it
bg to background it

23. jobs
The jobs command can give you a list of suspended and running jobs
fg and bg take “%n” as an arugment, where n is the number of the job as shown by “jobs”

24. killing processes
kill can take a job number (from 'jobs') or a process id (from ps)
kill -9 can kill off more stubborn processes
Don't use it unless kill doesn't work

25. Unix Utilities df Lists free space on filesystem du
shows disk usage – ideal for finding large files in your home directory
file
attempts to identify a file's contents