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• Your local system administrator should be your first point of contact
• The EITS Helpdesk provides e-mail and phone support to UGA faculty, staff and students for general computing-related questions
• e-mail: helpdesk@listserv.uga.edu
• phone: 542-3106

• e-mail: wsg@listserv.uga.edu
• phone: 542-3106

• All the basic commands are the same. Differ mainly at the programmer's level.
• Major versions are the Berkeley Standard Distribution (BSD) and AT&T System V.
• Some Workstation Variants: SunOS & Solaris(SUN), AIX(IBM), IRIX(SGI), ULTRIX(DEC), HP-UX(HP)
• Some PC & Mac Variants: BSDI, LINUX, SCO, ESIX, XENIX, AUX

• A shell is a program that reads commands and executes them.
• The common shells are the C shell (csh), the Bourne shell (sh), and the Korn shell (ksh).
• The shells differ in scripting syntax and a few other minor ways.
• You may be able to change your login shell using the chsh command.

• If the following files exist in your home directory, they will be executed whenever you login:
  • csh: .cshrc and .login
  • sh and ksh: .profile
• Place commands or tasks into these files that you would like performed whenever you login.

csh:

alias dir 'ls -l'

sh:

dir() /bin/ls -l $*

ksh:

alias -x dir='ls -l'

• Shell variables are simply strings of characters that hold other values, for example, $HOME may stand for /home/jones.
• Shell variables are indicated to the shell by a "$" as the first character.
• To see all of your built-in shell variables, use the set command.

Examples:

$HOME

$myvar

• To see the value of a specific shell variable, use the echo command:

• $HOME your login directory
• $PATH directories that will be searched for commands
• $TERM your terminal type
• $DISPLAY your local hostname for X windows applications

• csh:

  setenv PATH /usr/bin:/bin

  setenv PATH $PATH\:$HOME/bin

• sh, ksh:

  PATH=/usr/bin:/bin

  export PATH

  PATH=$PATH\:/usr/bin:/bin

  export PATH

command -options parameters

Example:

ls -l /home/jones/dir1

? - substitute any character at that position: file?.txt (file1.txt, file2.txt, ...)
* - substitute any number of any character(s) at that position: file*.txt (file1.txt, file1a.txt, file.txt, ...)

• Shell variables in commands are expanded by the shell.
• Shell variables are indicated by a "$" as the first character (e.g. $PATH, $HOME).

  Examples:

  echo $PATH

  cd $HOME

  ls $dir1

<

Read standard input from file

>

Write standard output to new file

>>

Append standard output to file

|

Send standard output from the first command to the standard input of the next

Examples:

ls > dir.list

ls $dir1 | more

• The general form is a tree.

The top of the tree, commonly called the root, is denoted by a single forward slash (/). All files are located "below" the root directory.

• Absolute paths begin with a slash:

  more /home/jones/adir/kermit.txt

• Relative paths (no slash at the beginning) start their search in the current directory:

  more adir/kermit.txt

• Filenames with no paths are presumed to be in the current directory:

  more kermit.txt

• Show the current directory with the pwd command.
• The cd command (change directory) is used to move around the directory tree.

  Examples for the tree given above are:

  cd /

  cd /usr/jones

  cd

• There are two special relative path symbols, '.' and '..' . These indicate the current directory (.) and its parent (..).

  Examples:

  ls ../smith

  cd ..

• Create new directories with the mkdir command. It makes the named directory.
• Some UNIX systems allow creation of many levels of directory at once.

  Examples:

  mkdir project

  mkdir project/data

• Delete a directory with the rmdir command.
• The directory to be deleted must be empty of both files and other directories.
• Directories must be deleted from the bottom up.

  Examples:

  rmdir project/data

  rmdir project

• Print one or more files to the screen:

  Example:

  cat filename(s)

• Create a file:

  Example:

  cat > x.y <ENTER>
  type in
  some text
  ^d (ends the input)

• Concatenate (append) files:

  Example:

  cat a b c > d

• Rename a file:

  Example:

  mv a.dat a.old

• Move a file to a different place in the filesystem:

  Examples:

  mv a.dat ../save (directory)

  mv a.dat ../save/a7.old

• The destination file is replaced if it exists.
• The original file is removed, so use with caution.

• The cp command copies a file from one name or place to another.

  Examples:

  cp a.dat a.old

  cp a.dat ../save (directory)

  cp a.dat ../save/a.old

• The destination file is replaced if it exists.

• The rm command is used to remove or delete one or more files.
• The -i option will ask you about each file to be removed.
• There is no way to recover a file after it has been removed.

  Examples:

  rm x.y

  rm a.dat b.dat c.dat d.dat

  rm -i *.o

• The ls command lists the files in directories.

  Some of the more common options are:

  -F     Flag type of file with "/", "*", "=", "@"
  -l     List files in a long, descriptive format
  -a     Show all entries, including "dot" files
  -t     List files in reverse order of time created
  

  Examples:

  ls

  ls -Fla

  ls -Fla *.c

  ls -Fla adir (directory)

• The find command locates specified files and lets you perform a number of actions on (or to) them.
• find will search recursively down the directory tree starting at the directory specified on the command line.
• find uses words for options, not single letters.

  Some of the more common options are:

  -name fn look for the filename specified

  -print print the filenames found

  -exec cmd run the command "cmd"

  -newer fn find files newer than the file "fn"

  Examples:

  find . -name slides.txt -print

  find / -name \*.c -print

  find / -name \*.old -exec rm -i {} \;

• The file command is used to determine the type of contents of a file.
• Use this before using either cat or more to look at a file at a terminal.
• Types are: text, binary executable, commands, data, etc.
• Never bring binary executable files to a terminal and be careful with data.

  Examples:

  file x file * | more

• The more command is used to look at the contents of a file, one screenful at a time.
• more also allows you to break up output to standard output to one screen at a time.
• To continue, press the spacebar; to quit, "q"
• For help, press "h" while more-ing a file.

  Examples:

  more letter.doc

  more *.doc

  ls /usr/lib | more

• The tail command displays the end of a file.
• Specify the number of lines displayed by including a number preceded by a "-".
• The tail of a file being created by another process may be viewed continuously (this flag varies from system to system; check the tail man page).

  Examples:

  tail letter.doc

  tail -100 letter.doc | more

• diff reports differences between files.
• Output lines are flagged with "<" for the first file and ">" for the second file.

  Example:

  diff file1 file2

  1c1
  < this is file1
  ---
  > this is file2
  

• Unix is a multiuser, multitasking operating system (task = process).
• On a Unix system, it is possible to run many programs and commands (processes) at the same time.
• Each user can have multiple processes running at the same time.
• The ps command is used to look at processes running on the system.
• The arguments to and output from this command depends on the flavor of Unix that you are running.
• ps by itself will show all running processes that are associated with your current terminal.

  
  

  Example of output from ps

  PID TTY TIME CMD 
  16035 pts/1 0:00 ps 
  19628 pts/1 0:00 ksh 
  

• System V systems (AIX, IRIX, Solaris, Linux):
  • ps -ef all processes, full listing
  • ps -fu user all processes associated with user, full listing
• BSD systems (SunOS, AIX, BSD/OS):
  • ps aux all processes, full listing
  • ps u all processes associated with running user, full listing

It is possible, however, to run commands and programs detached from the controlling terminal; this is known as running in the background. To run a command in the background, place an ampersand (&) at the end of the command line.

Example: Find all the files in your directories that end in .txt and list them, but don't wait for the command to complete:

find $HOME -name \*.txt -print > txt.list &

Note that the output is redirected to a file - otherwise, it would be sent to standard output and may interfere with what else you are doing.

• If the program expects input from the keyboard, this input must be redirected from a file or else the program will fail.

• Typical session:

  runme > cmd.out &
  [1] 19518
  jobs
  [1] + Running runme > cmd.out &
  [1] + 19518 Done runme > cmd.out &
  

• The number in square brackets is the jobid and is identified by a leading "%"

• jobs -- list your background jobs
• kill pid -- kill the specified process

  Example:

  kill 12345

• kill %jobid kill the background job

  Example:

  kill %1

• ^z suspend the current interactive job

• bg put a suspended job in the background
• fg %jobid bring a background job to the foreground
• nohup continue to execute the command after you log out, i.e., make the command immune to hangups:

  Example:

  nohup command &

• See the manual page for your shell (csh, ksh etc.) for additional job control commands

• There are a number of commands built into Unix to provide the ability to archive and compress files.
• A number of public domain programs are also available.

• The tar command is used to write data to tape and create multi-file archives on disk.

• Examples:

  Create file containing all files in a directory:

  tar cvf files.tar adir

  Extract these files:

  tar xvf files.tar

  List the files in the tar archive:

  tar tvf files.tar

• Use the compress command to shrink files. The compress command will add a ".Z" to the end of the compressed file:

  compress letter.doc

• To look at the contents without uncompressing, use the zcat command:

  zcat letter.doc.Z |more

• Run uncompress to restore them:

  uncompress letter.doc.Z

• Often, tar and compress are used together to create file archives for storage or distribution.
• These files will have a name of the form "something.tar.Z"
• To look at the contents of a ".tar.Z" file:

  zcat files.tar.Z | tar tvf - | more

• To untar the file:

  zcat files.tar.Z | tar xvf -

• gzip (Gnu zip) is a public domain compression program. The standard suffix added is ".gz" or ".z"

• To zip files:

  gzip file.txt

• To unzip files:

  gunzip file.txt.gz

• To look at the contents without unzipping the file:

  gunzip -c file.txt.gz

• Other commands may be available, including:
  • zip and unzip - compatible with DOS zip. File suffix is ".zip". This is a public domain program and not included with the standard Unix operating system.
  • pack and unpack - usually included with Unix. These files have the suffix ".z"