How to run a shell program

1
Decisons in Shell Programming
2
The if construct

• The general format of the if command is
• Every command has exit status
• If the exit status is zero, then the commands
  that follow between the then and if are executed,
  otherwise they are skipped

if command then command command fi
3
exit status

• Whenever any program completes execution, it
  returns an exit status back to the system
• status is a number
• status 0 program executed successfully
• status of nonzero program executed unsuccessfully

4
The ? Variable

• The shell variable ? Is automatically set by the
  shell to the exit status of the last command
  executed

5
The ? Variable (continue.)

• touch file1
• cp file1 file2
• echo ?
• 0
• cp file3 file1
• cp cannot access file3
• who
• hyunku console Jan 24 0016 (0)
• hyunku pts/4 Jan 24 0016 (0.0)
• sbenayed pts/5 Jan 251 1201
  (216.87.102.199)
• who grep abuzneid
• echo ?
• 1
• who grep sbenayed
• sbenayed pts/5 Jan 25 2101
  (216.87.102.199)
• echo ?
• 0

6
The test command

• Format test expression
• test evaluates expression, and if the result is
  true, it returns an exit status of zero,
  otherwise the result is false
• test "name" Alice
• Operator () separates arguments which means it
  must be surrounded with white space characters
• It's a good programming practice to enclose shell
  variables that are arguments to test inside a
  pair of doubles quotes

7
The test command (continue.)
name test name Alice test argument
expected test "name" Alice
Alice
test
arguments
test name Alice without name null
8
The test command (continue.)
null Alice
arguments
test
test name Alice with name null
9
File operators in test command
10
File operators in test command (continue.)
11
String operators in test command (continue.)
12
Integer Comparison Operators in test command
(continue.)
13
The test command (continue.)
14
Example test String Operator

• test can be quite picky about its arguments
• The operator has its highest precedence than
  the z operator, so test expects an argument to
  follow
• To avoid this sort of problem
• test X "symbol'X

blanks" " test blanks echo ? 1 test
"blanks" echo ? 0
15
An Abstract format to test

• test expression ? expression
• Spaces must appear after and before

if "name Alice gt then gt echo "Hello
Alice" gt fi echo ? 0
16
Example test Integer Operator

• X1"005"
• X2" 10"
• "X1" 5
• echo ?
• 1
• "X1" -eq 5
• echo ?
• 0

17
Example test File Operator

• To test if the file exits
• -f /home/abuzneid/UNIX/aaa
• To test is the file exists and is also readable
  by the user
• -r /home/abuzneid/UNIX/aaa

18
The Logical Negation Operator !

• The unary logical operator ! can be placed in
  front of any other test expression to negate the
  result of the evaluation of that expression
• ! -r /home/abuzneid/UNIX/aaa
• returns true if /home/abuzneid/UNIX/aaa is not
  readable
• ! "X1" "X2"
• returns true if X1 is not identical to X2 and
  is equivalent to
• "X1" ! "X2"

19
The Logical AND Operator -a

• Returns true only, if the two joined expressions
  are both true
• ! -f "myfile" a r "myfile"
• Returns true if myfile is an ordinary file and
  is readable by the user
• Parentheses can be used in test expression
• \( "count" ge o \) -a \(
• "count" 1t 10 \)

20
The Logical OR Operator -o

• Returns true if either the first expression is
  true or the second expression is true
• The o operator has lower precedence than the a
  operator
• "a" eq 0 o "b" eq 2 a "c" eq 10
• gets evaluated by test as
• "a" eq 0 o ("b" eq 2 a "c" eq 10)
• Parentheses can change the order if necessary

21
The else Construct

• if commandt
• then
• command1
• command2
• else
• command3
• command4
• fi

22
The exit Command

• Exit immediately terminates execution of a shell
  program
• exit n
• n the exit status that you want to be returned
• If n is not specified, then the exit status used
  is that of the last command executed before the
  exit

23
The elseif Construct

• if command1
• then
• command
• command
• else
• if command2
• then
• command
• command
• else
• if commandn
• then
• command
• command
• else

24
The elif Construct (continue.)

• if command1
• then
• command
• command
• elif command2
• then
• command
• command
• elif commandn
• then
• command
• command
• else
• command
• command

25
The elif Construct (continue.)

• command1, command2commandn are executed in turn
  and their exit status tested
• As soon as one returns an exit status of zero,
  the commands listed after the then that follows
  are executed up to another elif, else, or fi
• If none of the command returns a zero status,
  then the commands listed after the optional else
  are executed

26
The case Command
case value in pat1) command command
command pat2) command command
command patn) command
command command esac
27
The case Command

• The word value is compared against the values
  pat1, pat2, until a match is found
• When a match is found, the commands listed after
  the matching value, up to the double semicolons,
  are executed
• The shell lets you use ,?, special characters
  with shell
• The symbol has the effect of a logical OR when
  used between two patterns
• Pat1 Pat2

28
The null Command

• The format of null command is
• Example suppose you want to check to make sure
  that the value stored in the variable var exists
  in the file /home/abuzneid/.profile, and if it
  doesn't, you want to issue an error message and
  exit from the program

29
The null Command (continue.)

• if grep "var" /home/abuzneid/.profile
• gt then
• gt hello
• gt else
• gt echo "var does not exit.
• gt exit
• gt fi

30
The Construct

• command1 command2
• Example
• sort file1 gt /tmp/file2 mv /tmp/file2 file1
• The mv command will be executed only if the sort
  is successful

If ?!0
If ?0
31
The Construct

• command1 command2
• Example
• grep "name" phonebook echo "couldnt find
  name"
• Example
• who grep "name" gt /tmp/null echo "name
• is not logged on"

If ?0
If ?!0
32
The Construct (continue.)

• if command1 command2
• then
• Command3
• fi

• command3 will be executed if command1 or command2
  returns zero

33
Shell Script on

• Checks if a user is logged in or not
• To view on click here

on Incorrect number of arguments Usage on
user on abuzneid abuzneid is logged on on
sobh sobh is not logged on
34
Shell Script greetings

• Prints greeting wherever you logged in the system
• To view greetings click here

greetings Good morning
35
Shell Script rem

• Removes someone from the phonebook
• To view rem click here

rem Incorrect number of arguments. Usage rem
name rem Abdelshakour rem 'Abdelshakour
Abuzneid' I coudn't find Abdelshakour Abuzneid in
the phone book rem Susan More than one match
please qualify further rem 'Susan Clinton'
36
Shell Script number

• Translates a digit to english
• To view number click here

number 9 nine number 88 Bad argument please
specify a single digit number Usage number
digit
37
Shell Script charis

• Classify character given as argument
• To view charis click here

charis q Please type a single character
charis 9 Please type a single character charis
7 Please type a single character sh -x charis
9 1 -ne 1 char9 echo 9 wc -c numchars
2 2 -ne 1 echo Please type a
single character Please type a single character
exit 1
38
Shell Script charis2

• Classify character given as argument--version 2
• To view charis2 click here

charis2 t lowercase letter charis2
'gt' special character charis zzz Please type a
single character
39
Shell Script greetings2

• Program to print a greeting case version
• To view greetings2 click here

date Thu Jan 25 091408 EST 2001
greetings2 Good Morning
40
Loops in Shell Programming
41
The for Command

• for var in word1 word2wordn
• do
• command
• command
• done

42
The for Command (continue.)

• There is many ways to pass files to for
• 1.
• for file in f1 f2 f3 f2
• do
• run file
• done
• 2.
• for file in f1-4
• do
• run file
• done

43
The for Command (continue.)

• 3.
• for file in
• do
• run file
• done
• 4.
• for file in 'cat filelist'
• do
• run file
• done

44
The _at_ Command

• Replaces when argument are passed to for
• To view args click here

args a b c number of arguments passed is
3 a b c args 'a b' c number of arguments passed
is 2 a b c
45
The _at_ Command (continue.)

• shell replaces the value of with 1, 2
• shell replaces the value of _at_ with "1", "2"
• The double quotes are necessary around _at_, as
  without them this variable behaves just like

46
The _at_ Command (continue.)

• args -- version 2
• To view args2 click here

args2 a b c number of arguments passed is
3 a b c args2 'a b' c number of arguments
passed is 2 a b c args number of arguments
passed is 0
47
The for without the list

• Shell will automatically sequence through all of
  the arguments typed on the command line, just as
  if you had written in "_at_"
• To view args3 click here

args3 a b c number of arguments passed is
3 a b c args3 'a b' c number of arguments
passed is 2 a b c
48
The while Command
while command1 do command command done

• command1 is executed and its exit tested
• If it's zero, then the commands enclosed between
  do and done are executed
• Then process continues until command1 returns
  nonzero status

49
Shell Program printargs

• Print command line arguments are per line
• To view printargs click here

printargs a b c a b c printargs 'a b' c a b c
50
Shell Program printargs (continue.)
printargs Documents args args2 args3 charis gr
eetings mail memos number on personal phonebook pr
intargs Rem printargs
printargs Documents args args2 args3 charis gr
eetings mail memos number on personal phonebook pr
intargs Rem printargs
51
The until Command
until command1 do command command done

• The while command continues execution as long as
  the command listed after the while returns a zero
  exit status

52
Shell Script monitor

• Waits until a specified user log on
• To view monitor click here

monitor Usage monitor user monitor
abuzneid abuzneid has logged on
53
Shell Script monitor2

• Wait until a specified user log on -- version2
• To view monitor2 click here

monitor2 abuzneid -m Usage monitor2 -m user
-m means to be informed by mail monitor2
abuzneid abuzneid has logged on monitor2 -m
abuzneid 4290
54
Breaking out of a Loop

• break make an immediate exit from a loop
• true command returns zero exit status
• false command returns nonzero exit status
• break n
• The n innermost loops are immediately exited

55
Breaking out of a Loop (continue.)

• Example

while true do cmd 'getcmd' if "cmd" quit
then break else process cmd "cmd" fi done
56
Skipping the Remaining Commands in a Loop

• continue command causes the remaining commands
  in the loop to be skipped
• continue n
• causes the commands in the innermost n loop to be
  skipped, but execution of the loops then
  continues normal

57
I/O Redirection on a Loop

• Input redirection into the loop applies to all
  commands in the loop that read their data from
  standard input
• Output redirection from the loop to a file
  applies to all commands in the loop that write to
  standard output
• Errors can be directed from the standard output
  to a file by using 2gt after the done

58
I/O Redirection on a Loop (continue.)

• Example

• for i in 1 2 3 4
• gt do
• gt echo 1
• gt done gt loopout
• cat loopout

59
Piping Data into and out of a Loop

• loop will be run as a subshell
• Example

for i in 1 2 3 4 gt do gt echo i gt done wc -l
4
60
Typing a loop on one line

• loop will be run as a subshell
• Example

for i in 1 2 3 4 gt do gt echo i gt done wc -l
4 if 1 1 then echo yes fi yes
if 1 2 then echo yes else echo no fi no
61
The getopts command

• Shell provides getopts command to process command
  line arguments
• Format getopts options variable
• getopts should be executed inside a loop
• Checks if the argument one after one

62
The getopts command (continue.)

• getopts returns a zero exit status if
• The argument begins with minus sign and followed
  by any signal letter contained inside options.
  The argument will be saved inside specified
  variable
• The letter follows the minus is not listed in the
  options. It also stores ? inside variable. It
  also writes an error message to the standard error

63
The getopts command (continue.)

• getopts returns a nonzero exit status if
• There are no more arguments left on the command
  line
• The next argument doesn't start with minus sign
• abc option
• where the command can be executed as
• command a b c
• or using stacking feature as
• command -abc

64
The getopts command (continue.)

• getopts mt option
• where option t has an argument
• At least one white space character separates the
  option from the argument, such option cannot be
  stacked
• The argument will be stored inside a special
  variable called OPTARG
• OPTIND variable is initially set to one, and is
  updated each line getopts returns to reflect the
  number of the next command line argument to be
  processed

65
Shell script monitor3

• Wait until a specified user log on version3
• To view monitor3 click here

monitor3 -m Missing user name! monitor3 -x
abuzneid monitor3 illegal option -- x Usage
monitor3 -m -t n user -m means to be
informed by mail -t means check every n
secs. monitor3 -m -t abuzneid 5614
66
Reading Data
67
read Command

• Format read variables
• Shell reads a line from standard input and
  assigns the first word read to the first variable
  listed in variables, the second word read to the
  second variable, and so on
• Example read x y
• Reads a line from standard input, storing the
  first word read in the variable x, and the
  reminder of the line in the variable y

68
Serial echo Escape characters
69
Shell script mycp

• copy a file
• To view mycp click here

ls Unix creation1.sql function1.sql
procedure1.sql ls UNIX
70
Shell script mycp (continue.)
mycp Usage mycp file1 file2 mycp
file(s) dir cp mycp /home/abuzneid cd ..
chmod x mycp mycp creation1.sql function1.sql
procedure1.sql UNIX ls UNIX creation1.sql
function1.sql procedure1.sql
71
The variable and Temporary Files

• contains the process id number of the current
  process
• You can use to create a unique file name
• echo Hellogt/tmp/hello

for i in 1 2 3 4 gt do gt echo i gt done wc -l
4
72
The Exit Status from read

• read can read any number of lines from
• terminal
• file
• read always return zero exit status unless an end
  of file condition detected on the input
• CTRL-d from the terminal
• no more data to read from the file

73
The script addi

• adds pairs of integer on standard input
• To view addi click here

addi 10 25 35 -5 -10 -15 122 3 125 cat
data 19 20 -5 -10 20 10 addi ltdatagtsums cat
sums 39 -15 30
74
The script mynl

• number lines from files given as argument or from
  standard input if none supplied
• To view mynl click here

who mynl 1 hyunku console Jan 24 0016
(0) 2 hyunku pts/4 Jan 24 0016
(0.0) 3 sbenayed pts/5 Jan 26 1005
(1Cust132.tnt64.nyc3.da.uu.net)
75
References

• UNIX SHELLS BY EXAMPLE BY ELLIE QUIGLEY
• UNIX FOR PROGRAMMERS AND USERS BY G. GLASS AND K
  ABLES
• UNIX SHELL PROGRAMMING BY S. KOCHAN AND P. WOOD