The UNIX

1
Software Tools

• The UNIX
• Shell

2
Basic Shell Syntax

• command -options arg arg
• The name of the command is first
• Options are normally single letters that turn an
  option on or off. They can be combined or given
  separately.
• ls -dil
• ls -l -d -i
• Options sometimes also take a value. The value
  can usually be either given right after the
  option or separately
• ypcat -d ug.cs.ust.hk passwd

3
Command Options

• Most commands require you to give all options
  before filename arguments. The following command
  works in Linux, but not SunOS
• cat names -n
• George W. Bush
• Bill Gates
• Bill Gates
• Bill Clinton
• George W. Bush
• cat cannot open n
• Spaces separate options. To turn something with
  spaces into a single argument, use quotes
• grep vote thing letter1
• grep cant open thing
• letter1You have the Florida vote thing
• grep vote thing letter1
• You have the Florida vote thing

4
Command Options

• Double quotes and single quotes are a bit
  different. For now, you can use them
  interchangeably.
• grep vote thing letter1
• You have the Florida vote thing
• To escape a single character (prevent it from
  being treated specially) proceed it with a
  backslash
• grep We\ll letter2
• by my office. We'll tidy up a few more things
  before
• echo
• echo
• echo \
• echo
• letter1 letter2 names secret/

5
How Does the Shell Find a Command?

• The shell searches a list of directories for an
  executable file with the same name.
• The list of directories is stored in the PATH
  variable for Bourne shells and in the path array
  for csh/tcsh
• PATH/usr/local/binPATH sh
• set path(/usr/local/bin path) csh, tcsh
• If there is a match in more than one directory,
  the shell uses the first one it finds.
• If you want to run a command that is not in one
  of these directories, you can give a pathname
  (relative or absolute) instead.
• horner/bin/csound

6
How Does the Shell Find a Command?

• A few commands are built into the shell. This
  varies from shell to shell. The echo command, for
  example, is often builtin, for efficiency.
• You can find out where the shell is getting a
  particular command using the which command in
  any shell
• which echo
• echo shell built-in command.
• which cat
• /bin/cat
• which grep
• /bin/grep
• which ls
• ls aliased to ls --colortty

Makes directories blue, executables green, and
soft links aqua
7
Alias

• The C Shell has the alias command, which allows
  you to create command shortcuts.
• alias ls "ls -F"
• alias rm "rm -i"
• alias "chmod ux "
• alias - "chmod u-x "
• alias 111 "cd horner/111"
• pwd
• /bin
• 111
• pwd
• /homes/horner/111
• On most Unix machines (except Mandriva/Mandrake
  in CSLab2), if you put the alias commands in your
  .cshrc file, you can use them every time you
  login.

8
Standard Input

• Every time you login, or run a shell, you are
  connected to the computer on a particular
  terminal.
• who
• horner pts/3 Feb 14 1023
  (csnt1.cs.ust.hk)
• horner pts/0 Feb 14 1157
  (csz096.cs.ust.hk)
• These devices (pts/0) are actually files in the
  directory /dev. So, if you are logged in on
  pts/0, this works just fine
• date gt /dev/pts/0
• Mon Feb 14 170821 HKT 2005

9
Standard Input

• In fact, you can redirect stdout to a different
  device (e.g., pts/3), if you have permission.
  (The write command works this way.)
• You can find out which terminal a particular
  shell is connected to using the tty command
• tty
• /dev/pts/0
• echo "Hi Andrew!" gt /dev/pts/3

10
Tee

• A special command called tee acts like a T-joint
  in plumbing
• who
• horner pts/3 Feb 14 1023 (csnt1.cs.ust.hk)
• horner pts/0 Feb 14 1157
  (csz096.cs.ust.hk)
• who sort tee sortedwho wc -l
• 2
• cat sortedwho
• horner pts/0 Feb 14 1157
  (csz096.cs.ust.hk)
• horner pts/3 Feb 14 1023 (csnt1.cs.ust.hk)
• In this example, the output of sort is placed
  in a file sortedwho and piped to wc -l, which
  counts the number of lines.

11
Background Jobs

• A simple command or pipeline can be put into the
  background by following it with the
  character
• sort names gt names.sort
• 1 3236
• The shell will print the process ID (PID), and a
  job number (1, in this case).
• In some shells, you will be notified when the job
  is done (you may have to hit return again)
• sort names gt names.sort
• 1 3236
• 1 Done sort names gt names.sort

12
Background Jobs

• Put a job in the background by typing CTRL-Z
• ypcat passwd sort gtpasswd.sort
• Z
• Suspended
• The job is suspended - not running - until you
  either place it in the background using bg
• bg
• 1 ypcat passwd sort gt passwd.sort
• or back to the foreground using fg
• fg
• ypcat passwd sort gtpasswd.sort

13
Jobs

• The jobs command tells you what jobs are running
• ypcat passwd sort gt passwd.sort
• Z
• Suspended
• jobs
• 1 Suspended ypcat passwd sort gt
  passwd.sort
• You can stop a job with the kill command
• ypcat passwd sort gt passwd.sort
• 1 3414 3415
• kill 1
• 1 Terminated ypcat passwd
• Exit 2 sort gt passwd.sort
• The 1 means job 1. You can also use the PID.

14
Jobs

• The ps command is the main way to find out about
  jobs
• ps
• PID TTY TIME CMD
• 1401 pts/0 001 csh
• ypcat passwd sort gt passwd.sort
• 1 3476 3477
• ps
• PID TTY TIME CMD
• 3477 pts/0 000 sort
• 1401 pts/0 001 csh
• 3476 pts/0 001 ypcat

15
Jobs

• Note that if you put something into the
  background, you better redirect stdout, or the
  output will appear on your screen anyway!
• ypcat passwd
• ma_wmkaauq2jXK0sFQ8Jg367475000Woo Man
  Kei,,EXP.2001.05.30nc99S/homes/ma_h
• ma_chyaaCS9wq.1zOxnhI354355000Chu How Yin
  Agnes,,EXP.2001.05.30nc98F/homs
• ee_tkcaa9LtI7Tipk2Ca6356515000Tsang Kong
  Chau,,EXP.2001.05.30nc99S/homesh
• eg_cckyi7XtKxxP5KaQ4355510010Cheung Chi
  Keung,,ce98_yr1/homes/eg_cck/bin/h
• cs_wksdtjvwifI2G7v22451410001Wong Kin
  Shing,,cs98_yr1/homes/cs_wks/bin/tch
• cs_lwkOWiGoJRXSjn.s2403210001Leung Wai Kei
  Ricky,,cs98_yr2/homes/cs_lwk/bh
• ph_chyacCSJUo9e2KGqKg359555000Chan Hoi
  Yan,,EXP.2001.05.30nc98F/homes/phs
• ee_wkkabdfbi3GqWjvf5U356445000Wong Ka
  Keung,,EXP.2001.05.30nc99S/homes/eh
• ph_lcyCSwGgr5IeIvqc366895000Lam Chi
  Yin,,EXP.2001.05.30nc99S/homes/ph_lcx
• C
• ypcat passwd gtfile

16
More Pattern Matching

• The notation abcd matches any single one of
  the enclosed characters.
• ls il
• it it1 ith its_at_ letter1
  letter4
• The notation a-z matches any lowercase
  letter.
• The notation 0-9 matches any digit character.
• The notation 0-59 matches any the digit
  characters 0, 1, 2, 3, 4, 5, and 9.
• ls letter
• letter1 letter4
• ls letter0-35
• letter1
• ls letter0-24
• letter1 letter4

17
More Pattern Matching

• Most shells allow you to give a list of strings
  in curly brackets, comma separated
• ls 1,.sort
• NAMES1 it1 names.sort s1_at_
• f1 letter1 passwd.sort
• secret1
• secret1 Permission denied

18
Switching Shells

• You can switch shells by just typing its name
• csl2wk01.cs.ust.hkgt ps
• PID TTY TIME CMD
• 3496 pts/0 001 csh
• csl2wk01.cs.ust.hkgt tcsh
• csl2wk01.cs.ust.hkgt ps
• PID TTY TIME CMD
• 3650 pts/0 000 tcsh
• 3496 pts/0 001 csh
• csl2wk01.cs.ust.hkgt sh
• ps
• PID TTY TIME CMD
• 3650 pts/0 000 tcsh
• 3496 pts/0 001 csh
• 3659 pts/0 000 sh
• D
• csl2wk01.cs.ust.hkgt ps
• PID TTY TIME CMD
• 3650 pts/0 000 tcsh

19
Combining Commands

• Multiple pipelines can be input on one command
  line by separating them with semicolons.
• When entering a long command, use a backslash (\)
  to continue the command on the next line.
• date sort names \
• who
• Mon Feb 14 194028 HKT 2005
• Bill Clinton
• Bill Gates
• Bill Gates
• George W. Bush
• George W. Bush
• horner pts/3 Feb 14 1023
  (csnt1.cs.ust.hk)
• horner pts/0 Feb 14 1911
  (csz096.cs.ust.hk)

20
Combining Commands

• Commands can be grouped together using
  parentheses
• There are two main reasons to group commands
• To create a single command out of a group of
  commands (especially useful before a pipe)
• (cat letter1 head -2 names) sort gtlist
• To run a set of commands in their own subshell
  (especially when trying to limit the effect of a
  cd command)
• (cd secret ls wc -l) ls wc -l
• 3
• 25
• This line has the effect of counting the files
• in secret, and then counting the files in the
• current directory.