Unix Scripting…

Some General Ramblings…

2

Quoting

Single quote: '...' The shell ignores all enclosed characters

Double quote: "..." The shell ignores most enclosed characters The shell does interpret $, `, and \

Backtick or Lefttick: `...` Runs a command output treated as a

variable

Backslash: \ Special treatment for the following character.

3

Setting Variables

Setting variables var=value ENVVAR=value export ENVVAR

Note: variables don’t affect parent shells only environmental variables affect child

shells

4

Using variables

“$*” - list of all command-line parameters. Bad.“$@” – Good list of all command-line parameters.“$1”, “$2”, …, “$9” – individual command line parameters

5

Shell Loops - ifif expr ; then cmd1 ; else cmd2 ; ficmd1 and cmd2 can be complexthe else can be omitted

$ if [ x"$var" = x"yes" ]> then> echo good> figood

if [ x“$var” = x“yes” ] ; then echo good ; fi

6

Shell Loops – while, for

while expr do

cmd done

for var in a b c d e do

cmd done

7

Shell functions

Act like mini-shell scripts.Can set variables in the current shell.

function-name () {

cmd1cmd2

}

8

Using the test Command

The test command makes preliminary checks of the UNIX internal environment and other useful comparisonsPlace the test command inside the shell script or execute it directly from the command lineThe test command can be used to:

Perform relational tests with integers Test strings Determine if a file exists and what type of file it is Perform Boolean tests

9

Relational Integer Tests

The test command returns a value known as an exit status, which is a numeric value and indicates the results of the test performed: true if 0 (zero) and false if 1 (one)

10

String Tests

11

Testing Files

12

Testing Files From The Prompt…

$ touch testfile$ ls -l testfile-rw-r--r-- 1 student student 0 Oct 9 11:45 testfile$ test -x testfile$ echo $?1 (Note: 0 = true and 1 = false)$ chmod 700 testfile$ ls -l testfile-rwxr-xr-x 1 student student 0 Oct 9 11:45 testfile$ test -x testfile$ echo $?0$ $ test -f test_file$ echo $?1

13

Performing Boolean Tests

AND – returns true (0) if both expressions are true, otherwise returns false (1)

OR – returns true if either expression is true, otherwise if neither is true, returns false

! – negates the value of the expression

14

Boolean Tests (testfile1 & testfile2)

touch testfile1test –f testfile1 –a –x testfile2Echo $?touch testfile2test –f testfile1 –a –x testfile2echo $?chmod 777 testfile1echo $?test –f testfile1 –a –x testfile2rm testfile2test –f testfile1 –a –x testfile2

15

Script Exercise 1

Write a script that will echo to the screen at least three arguments that you include at the command line when you run the script

16

Script Exercise 1 Solution

#!/bin/bashecho $1 $2 $2

17

Script Exercise 2

Write a script that will create a file that is named when you execute the shell scripte.g. myshell.sh testfile

18

Script Exercise 2 Solution

#!/bin/bashtouch $1# or…echo “testing” > $1# or…> $1# or…ls > $1

19

Script Exercise 3

Write a script that will create a file using today’s date and the date format is ddmmmyy.dat

20

Script Exercise 3 Solution

#!/bin/bashtouch `date +%d%b%y`.dat# or….FILENAME=`date +%d%b%y`.datTouch $FILENAME# or etc….

21

Script Exercise 4

Write a script that will ask the user for to input a file name and then create the file and echo to the screen that the file name inputted had been created

22

Script Exercise 4 Solution

#!/bin/bashclearecho ‘enter a file name: ‘read FILENAMEtouch $FILENAMEecho “$FILENAME has been created”

23

Script Exercise 5

Now take the script from exercise 4 and write it so it will not create a file if no input is received

24

Script Exercise 5 Solution#!/bin/bashclearecho ‘Enter a file name: ‘read FILENAMEif [ ! –z $FILENAME ] ; then

touch $FILENAMEecho “$FILENAME has been created”

elseecho “You did not enter a file name.”

fi

25

Script Exercise 6

Write a script that asks for the users favorite color then if it is not “red” inform them that is the wrong answer, wait 3 seconds, clear the screen and ask the question again.

26

Script Exercise 7

Ask the user to enter multiple entries (name, age, sex and favorite color) one at a time. Then echo those answers back to the screen.

27

Script Exercise 8

Modify the script in exercise 7 to write the responses to a file named “ddmmyy.dat” one answer per line.