Advanced UNIX CIS 218 Advanced UNIX 6 . The Bourne and Bash Shells - - PowerPoint PPT Presentation

CIS 218 Advanced UNIX 1

Advanced UNIX

 Objectives

– explain how to write Bourne and Bash Shell scripts

CIS 218 – Advanced UNIX

• 6. The Bourne and

Bash Shells

CIS 218 Advanced UNIX 2

Overview

1. Making a File Executable 2. Combining Commands 3. Redirecting Output 4. Executing Scripts 5. Variables 6. Control Flow

continued

CIS 218 Advanced UNIX 3

7. Functions 8. Other Commands 9. Here Documents

• 10. Debugging
• 11. More Information

CIS 218 Advanced UNIX 4

• 1. Making a File Executable

 $ cat whoson

date echo Users currently logged on who  Wrong: $ whoson whoson: Permission denied

CIS 218 Advanced UNIX 5

Right:

 $ ls -lg whoson

• rw-r--r-- 1 ad pubs 42 Jun 17 10:55 whoson

$ chmod u+x whoson $ ls -lg whoson

• rwxr--r-- 1 ad pubs 42 Jun 17 10:55 whoson

 $ whoson

Tue Nov 7 13:21:34 ICT 2000 Users currently logged in ad consol Nov 7 08:26 jenny tty02 Nov 7 10:04

CIS 218 Advanced UNIX 6

Possible PATH Problem

 $ whoson

whoson: Command not found  Due to PATH shell variable (see later)  Quick fixes: $ ./whoson

• r

$ sh whoson

CIS 218 Advanced UNIX 7

• 2. Combining Commands

 Sequencing:

$ a ; b ; c

 same as:

$ a $ b $ c

CIS 218 Advanced UNIX 8

Process Creation (&)

 $ a & b & c

14271

(PID for a)

14272

(PID for b)

 $ a & b & c &

14290 14291 14292 $

 $ a | b | c &

14302

(PID for piped commands)

CIS 218 Advanced UNIX 9

Processes in Action

$ cat a echo -n “aaaaaaaaaaaaaaaaaaaaa” echo -n “aaaaaaaaaaaaaaaaaaaaa” sleep 2 echo -n “aaaaaaaaaaaaaaaaaaaaa” echo -n “aaaaaaaaaaaaaaaaaaaaa”  Similarly for b and c  Try the following a few times: $ a & b & c & On calvin there isn't much variation unless the machine is loaded.

CIS 218 Advanced UNIX 10

• 3. Redirecting Output

 1>

redirect standard output (stdout) 2> redirect standard error (stderr)

$ cat a b 1> out 2> err cat a b

• ut

err stdout stderr Files

CIS 218 Advanced UNIX 11

>&

 redirect one stream into another:

– 2>&1 redirect stderr into stdout

$ cat a b 1> theLot 2>&1 cat a b theLot stderr stdout

CIS 218 Advanced UNIX 12

• 4. Executing Scripts

 Make sure that a script is executed by the

Bourne Shell:

$ sh whoson

(no need for chmod)

 or:

$ cat boss

#!/bin/sh echo Definitely Bourne Shell Script continued

CIS 218 Advanced UNIX 13

 On Linux machines (e.g. calvin), the

Bourne shell has been replaced by Bash

– sh means the Bash shell

CIS 218 Advanced UNIX 14

• 5. Variables

5.1. User-defined Variables 5.2. Environment Variables 5.3. Readonly Shell Variables

CIS 218 Advanced UNIX 15

5.1. User-defined Variables

 $ person=alex

$ echo person person $ echo $person alex

 $var returns the value stored in var

– called substitution

No spaces around the =

CIS 218 Advanced UNIX 16

5.1.1. Switch off Substitution

 Swich off substitution with 'var' or \var

 $ echo '$person'

$person $ echo \$person $person

CIS 218 Advanced UNIX 17

5.1.2. Switch off Special Chars (")

 "" switches off the special meaning of characters

used in filename generation (e.g. *, ?)

 $ ls

// directory contents ad.report ad.summary

 $ memo=ad*

$ echo "$memo" ad* $ echo $memo ad.report ad.summary * means only * * means any number

• f characters

CIS 218 Advanced UNIX 18

5.1.3. Exporting Variables

 Normally a variable is local to the running

script (the process).

 It is sometimes useful if running scripts

(processes) can access another script’s variables.

 e.g. extest subtest cheese=english calls we want to use cheese in subtest

CIS 218 Advanced UNIX 19

No Exporting: extest1 & subtest

 $ cat extest1

cheese=english echo "extest1 1: $cheese" subtest echo "extest1 2: $cheese" $cat subtest echo "subtest 1: $cheese" cheese=swiss echo "subtest 2: $cheese" continued Using " is a good habit, see later

CIS 218 Advanced UNIX 20

 $ extest1

extest1 1: english subtest 1: subtest 2: swiss extest1 2: english subtest does not see extest1's cheese value extest1 is not affected by subtest's setting of cheese

CIS 218 Advanced UNIX 21

Exporting: extest2 & subtest

 $ cat extest2

export cheese cheese=english echo “extest2 1: $cheese” subtest echo “extest2 2: $cheese”

 $ extest2

extest2 1: english subtest 1: english subtest 2: swiss extest2 2: english cheese value passed in change not exported from subtest

CIS 218 Advanced UNIX 22

5.1.4. Reading

 $ cat readln

echo -n “Type: ” read ln echo “You entered: $ln”

 $ readln

Type: The Wizard of Oz You entered: The Wizard of Oz read inputs everything up to the newline

CIS 218 Advanced UNIX 23

No Quotes

 $ cat readlnnq

echo -n “Type: ” read ln echo You entered: $ln

 $ ls

ad.report summary1 $ readlnnq Type: * You entered: ad.report summary1 directory contents

CIS 218 Advanced UNIX 24

5.1.5. Executing Commands

 $ cat proc_cmd

echo -n “Enter a command: ” read command $command echo Thanks

 $ proc_cmd

Enter a command: echo Display this Display this Thanks A very simple shell

CIS 218 Advanced UNIX 25

5.1.6. Splitting Input

 $ cat split3

echo -n “Enter something: ” read word1 word2 word3 echo “Word 1 is: $word1” echo “Word 2 is: $word2” echo “Word 3 is: $word3”

 $ split3

Enter something: this is something Word1 is: this Word2 is: is Word3 is: something Text is split based on white space.

CIS 218 Advanced UNIX 26

 $ split3

Enter something: this is something else, x Word1 is: this Word2 is: is Word3 is: something else, x The last variable gets everything that is left in the input.

CIS 218 Advanced UNIX 27

5.1.7. Command Subsitution

 $ cat mydir

this_dir=‘pwd‘ echo “Using the $this_dir directory.” this_date=$(date) echo "Today's date: $this_date"

 $ mydir

Using /home/ad/teach/adv-unix/bourne directory Today's date: Tue Nov 7 13:52:46 ICT 2000 $ A Bash addition Must use ‘

CIS 218 Advanced UNIX 28

5.2. Environment Variables

 Most environment variables get their

values from the shell at login.

 The values of some of the variables can be

set by editing the .profile file in your home directory

– Bash uses .bash_profile and .bashrc

CIS 218 Advanced UNIX 29

5.2.1. Examples

 HOME

pathname of your home directory

 $ pwd

/home/ad/planning $ echo $HOME /home/ad $ cd $ pwd /home/ad continued cd uses HOME to return to your home directory

CIS 218 Advanced UNIX 30

 PATH

– directories where executable can be found – represented as a string of pathnames separated by ‘:’s

 $ echo $PATH

/usr/local/bin:/usr/bin:/bin: $ PATH=SPATH":/home/ad/bin:." $ echo $PATH /usr/local/bin:/usr/bin:/bin:/home/ad/bin:. Extend the default PATH

CIS 218 Advanced UNIX 31

Note for SysAdmins

 If you are the system administrator

(superuser, root) for your machine, do not extend your path with "."

– it opens you to potential attack by hackers – e.g. 'fake' UNIX utilities placed in the current directory

CIS 218 Advanced UNIX 32

5.2.2. Typical .profile

 $ cat .profile

TERM=vt100 PATH=$PATH":/home/ad/bin:." PS1=“ad: “ CDPATH=:$HOME export TERM PATH PS1 CDPATH stty kill ^u

 $ . .profile

export needed in the Bourne shell

CIS 218 Advanced UNIX 33

5.2.3. Typical .bash_profile

 On calvin, .bash_profile simply invokes

your .bashrc (if it exists):

umask 002 if [ -f ~/.bashrc -a PS1="\$ " ]; then . ~/.bashrc fi continued These shell commands will be explained later

CIS 218 Advanced UNIX 34

Typical .bashrc

 PS1="\u@\h$ "

# PS1="\w[\#]$ " PATH=$PATH":." alias ls='/bin/ls -F' alias dir='ls -ba' alias cls="clear" : : psgrep() { ps aux | grep $1 | grep -v grep }

These features will be explained later. No export needed

CIS 218 Advanced UNIX 35

5.2.4. set

 The current settings for the environment

variables can be listed with set:

$ set | more BASH=/bin/bash : PATH=/usr/local/bin:/usr/bin:/bin:. : PS1='\u@\h$ ' :

CIS 218 Advanced UNIX 36

5.3. Readonly Shell Variables

 These are environment variables that

cannot have their values changed.

 Most of them relate to the arguments

supplied to a script when it is called.

CIS 218 Advanced UNIX 37

5.3.1. Script Name ($0)

 $ cat abc

echo The name of this script is $0

 $ abc

The name of this script is abc

CIS 218 Advanced UNIX 38

5.3.2. Script Arguments ($1, $2,..., $9)

 $ cat display_5args

echo The first five command line echo arguments are $1 $2 $3 $4 $5

 $ display_5args jenny alex helen

The first five command line arguments are jenny alex helen If the variable has no value, then nothing is printed.

CIS 218 Advanced UNIX 39

5.3.3. All Arguments ($*)

 $ cat display_all

echo $*

 $ display_all a b c de fg hi jk mno pqr

stu w x y z a b c de fg hi jk mno pqr stu w x y z

 $@ is like $* but puts “...” around each

printed argument

CIS 218 Advanced UNIX 40

5.3.4. Number of Arguments ($#)

 $ cat num_args

echo “This script has $# arguments.”

 num_args helen alex jenny

This script has 3 arguments

CIS 218 Advanced UNIX 41

5.3.5. The shift Commnd

 shift moves argument values on the

command line one $<number> to the left.

 Overcomes limit of 9 argument variables

($1, $2, ..., $9)

continued

CIS 218 Advanced UNIX 42

 $ cat demo_shift

echo “arg1= $1 arg2= $2 arg3= $3” shift echo “arg1= $1 arg2= $2 arg3= $3” shift echo “arg1= $1 arg2= $2 arg3= $3” shift

 $ demo_shift alice helen jenny june

arg1= alice arg2= helen arg3= jenny arg1= helen arg2= jenny arg3= june arg1= jenny arg2= june arg3= jenny "moves" to the left.

CIS 218 Advanced UNIX 43

5.3.6. The set Command (Again)

 set ‘cmd‘

(must use ‘)

– evaluates cmd and assigns its values to the script command line arguments ($1, $2, ..., $9, $*) – the values in cmd output are separated by whitespace

continued

CIS 218 Advanced UNIX 44

 $ date

Fri Jun 17 23:04:09 GMT+7 1996 $ cat dateset set ‘date‘ echo $* echo echo “Argument 1: $1” echo “Argument 2: $2” echo “Argument 3: $3” echo $2 $3, $6 continued The date values are assigned to $1, $2, etc.

CIS 218 Advanced UNIX 45

 $ dataset

Fri Jun 17 23:04:13 GMT+7 1996 Argument 1: Fri Argument 2: Jun Argument 3: 17 Jun 17, 1996

CIS 218 Advanced UNIX 46

• 6. Command Flow

6.1. Branching 6.2. Test Forms 6.3. Looping 6.4. break, continue, : 6.5. trap

CIS 218 Advanced UNIX 47

6.1. Branching

 $ cat same_word

echo -n “word 1: ” read word1 echo -n “word 2: ” read word2 if test "$word1" = "$word2" then echo Match fi echo End of Program Use " to stop filename expansion continued

CIS 218 Advanced UNIX 48

 $ same_word

word1: peach word2: peach Match End of Program

CIS 218 Advanced UNIX 49

 $ cat chkargs

if [ $# = 0 ] then echo Usage: chkargs argument... 1>&2 exit 1 fi echo Program running exit 0

 $ chkargs

Usage: chkargs argument... $ chkargs abc Program running Redirect stdout to stderr

6.1.1. Second Format

CIS 218 Advanced UNIX 50

6.1.2. if-then-else

 $ cat show

if [ $# = 0 ]; then echo Usage: show [-v] filenames 1>&2 exit 1 fi if [ “$1” != “-v” ] then cat “$@” else shift more “$@” fi C programmers prefer this format Use: $ show -v f1.txt f2.txt

CIS 218 Advanced UNIX 51

6.1.3. if-then-elif

 $ cat same3

echo -n “word 1: ” read word1 echo -n “word 2: ” read word2 echo -n “word 3: ” read word3 if [ “$word1” = “$word2” -a \ “$word2” = “$word3” ] then echo “Match: words 1, 2, and 3” continued For multiway branches

• a means "and"

\ means "continued

• n next line"

CIS 218 Advanced UNIX 52

elif [ “$word1” = “$word2” ] then echo “Match: words 1 and 2” elif [ “$word1” = “$word3” ] then echo “Match: words 1 and 3” elif [ “$word2” = “$word3” ] then echo “Match: words 2 and 3” else echo “No match” fi

CIS 218 Advanced UNIX 53

6.1.4. case

 $cat command_menu

#!/bin/sh # menu interface to simple commands echo “\n COMMAND MENU\n” echo “ a. Current date and time” echo “ b. Users currently logged in” echo “ c. Name of working directory” echo “ d. Contents of working directory” echo -n “Enter a, b, c, or d: ” read answer echo continued Better style: specify the shell, and comment the code.

CIS 218 Advanced UNIX 54

case “$answer” in a) date ;; b) who ;; c) pwd ;; d) ls -C ;; *) echo “$answer not legal” ;; esac echo * is the default; always include it at the end

CIS 218 Advanced UNIX 55

 $ command_menu

COMMAND MENU

• a. Current date and time
• b. Users currently logged in
• c. Name of working directory
• d. Contents of working directory

Enter a, b, c, or d: a Fri Jun 17 14:11:57 GMT 1996

CIS 218 Advanced UNIX 56

Other case Patterns

 ?

matches a single character

 [...]

any character in the brackets. Use - to specify a range (e.g. a-z)

 |

• r (e.g. a|A)

 *

it can be used to match "any number of characters"

CIS 218 Advanced UNIX 57

 $cat timeDay

#!/bin/sh echo Is it morning? Answer yes or no read timeofday case "$timeofday" in "yes" | "y" | "Yes" | "YES" ) echo "Good Morning" ;; [nN]* ) echo "Good Afternoon" ;; *) echo "Uhh??" ;; esac

CIS 218 Advanced UNIX 58

6.2. test Forms

 Format: test expr [ expr ]  e.g. test “$word1” = “$word2” [ “$1” != “-v” ] [ “$word2” = “$word3” ] [ “$word1” = “$word2” -a \ “$word2” = “$word3” ] Used in the conditions of if's and loops.

CIS 218 Advanced UNIX 59

6.2.1. String Expressions

 string1 = string2  string1 != string2  -n string

(true if string is not ““)

 -z string

(true if string is ““)

CIS 218 Advanced UNIX 60

6.2.2. Numerical Expressions

 number1 -eq number2

(equality)

 number1 -ne number2

(inequality)

 number1 -lt number2

(<)

 number1 -le number2

(<=)

 number1 -gt number2

(>)

 number1 -ge number2

(>=)

CIS 218 Advanced UNIX 61

6.2.4. File Test Expressions

 -f file

(file exists)

 -d file

(file exists but is a directory)

 -r file

(file is readable)

 -w file

(file is writable)

 -x file

(file is executable)

CIS 218 Advanced UNIX 62

6.2.5. Combining Expressions

 ! expr

(not expr)

 expr1 -a expr2

(and)

– Bash allows && as well

 expr1 -o expr2

(or)

– Bash allows || as well

 ( expr )

CIS 218 Advanced UNIX 63

6.3. Looping (for-in)

 Format: for loop-index in argument-list do commands done

CIS 218 Advanced UNIX 64

 $ cat fruit

for fruit in apples oranges pears do echo $fruit done echo Task completed

 $ fruit

apples

• ranges

pears Task completed

CIS 218 Advanced UNIX 65

Looking for “for” in files

 First version of script: $ car file-fors1 for f in ‘ls‘ do echo $f done

CIS 218 Advanced UNIX 66

 $ cat file-fors2

for f in ‘ls‘ do grep -i “for” $f > /dev/null if [ $? == 0 ] then echo $f fi done Ignore output

CIS 218 Advanced UNIX 67

6.3.1. for

 $ cat whos

# Give user details from /etc/passwd if [ $# = 0 ] then echo Usage: whos id... 1>&2 exit 1 fi for i # read as for i in “$@” do awk -F: ’{print $1, $5}’ /etc/passwd | grep -i “$i” done awk variables with ’

CIS 218 Advanced UNIX 68

6.3.2. while

 $ cat count

number=0 while [ $number -lt 10 ] do echo -n "$number" number=‘expr $number + 1‘ done echo

 $ count

0123456789 $

CIS 218 Advanced UNIX 69

Watching for Mary to log in

 while sleep 60

do who | grep mary done  Disadvantages:

– if Mary is already logged in, then we must wait 60 secs to find out – we keep being told that Mary is logged in

CIS 218 Advanced UNIX 70

6.3.3. until

 Format:

until command

do loop body until the command evaluates to true done  Watching (v.2): until who | grep mary do sleep 60 done loop until grep returns ‘true’ (0)

CIS 218 Advanced UNIX 71

6.3.4. Extending Watching

 Generalise so can watch for anyone:

$ watchfor ad

 Watch for everyone logging in/out: $ watchwho

CIS 218 Advanced UNIX 72

watchfor

#!/bin/sh # watchfor # watch for person supplied as argument if [ $# = 0 ] then echo “Usage: watchfor person” exit 1 fi until who | grep “$1” do sleep 60 done

CIS 218 Advanced UNIX 73

watchwho

 Once a minute, run who and compare its

• utput to that from a minute ago. Report

any differences.

 Keep the who output in files in /tmp  Give the files unique names by adding the

shell variable $$.

– $$ is the PID of the user’s shell

CIS 218 Advanced UNIX 74

#!/bin/sh # watchwho: watch who logs in and out new=/tmp/wwho1.$$

• ld=/tmp/wwho2.$$

> $old # create an empty file while true do who > $new diff $old $new mv $new $old sleep 60 done | awk ’/>/ {$1 = “in: “; print} /</ {$1 = “out: “; print}’

An advanced Shell programming technique: |

CIS 218 Advanced UNIX 75

Use

 $ watchwho

in: root tty1 Nov 6 09:32 in: ad pts/3 Nov 8 08:49 (myrrh.coe.psu.ac.th) in: s4010441 pts/5 Nov 8 10:11 (192.168.0.134) in: ad pts/4 Nov 8 10:12 (myrrh.coe.psu.ac.th) in: s4010143 pts/17 Nov 7 23:57 (192.168.0.204)

• ut: ad pts/4 Nov 8 10:12 (myrrh.coe.psu.ac.th)

in: ad pts/4 Nov 8 10:16 (myrrh.coe.psu.ac.th)

• ut: ad pts/4 Nov 8 10:18 (myrrh.coe.psu.ac.th)

:

initial users

CIS 218 Advanced UNIX 76

Notes

 diff uses ‘<‘ and ‘>‘ to distinguish data

from $old and $new

 $ diff old new

< ad > mary john ad

• ld

john mary new continued

CIS 218 Advanced UNIX 77

 The output from the while loop is piped

into awk

– only one call to awk is required – the "pipe" programming style

 A calvin problem: – awk had to be called with the -W interactive

• ption so that its output was not buffered

– otherwise nothing would appear

while loop awk

CIS 218 Advanced UNIX 78

6.3.5. Checking mail

 Have a script watch your mailbox

periodically, and report whenever the mailbox changes by printing “You have

mail”.  Usage: – $ checkmail # checks every 60 secs – $ checkmail 120 # checks every 120 secs

CIS 218 Advanced UNIX 79

checkmail

#!/bin/sh # checkmail: watch mailbox for growth time=${1-60}

• ldls="‘ls -l $MAIL‘"

while true do newls="‘ls -l $MAIL‘" echo $oldls $newls

• ldls="$newls"

sleep $time done | awk ’$5 < $14 {print “You have mail”}’

uses the pipe technique

CIS 218 Advanced UNIX 80

Notes

 $MAIL is a builtin shell variable, with the

value /var/spool/mail/$USER

 t=${1-60} sets t to $1 or, if no argument is

provided, to 60

– General form: ${var-thing} returns value of var if defined; otherwise

thing continued

CIS 218 Advanced UNIX 81

 Use awk to print a message only when the

mailbox gets bigger:

– awk $5 $14 compares the size fields of the two ls -l calls output at the end of each iteration e.g. $ ls -l foo

• rw-r--r-- 1 ad ad 34512 Nov 13 1996 foo

$ ls -l foo

• rw-r--r-- 1 ad ad 34512 Nov 13 1996 foo

5th value 14th value

CIS 218 Advanced UNIX 82

6.4. break, continue, :

 break and continue are used as in C:

– break escapes from a loop

for file in fred* do if [ -d "$file" ]; then # deleted? break # finish loop fi # do something # done

continued

CIS 218 Advanced UNIX 83

 continue goes to the top of a loop:

for file in fred* do if [ -d "$file" ]; then # deleted? continue # go back to loop top fi # do something # done

continued

CIS 218 Advanced UNIX 84

 The ':' command is the same as true, but

runs a tiny bit faster

– often used to simplify control logic

if [ -f fred ]; then # is fred a file? : # do nothing else # do something # fi

CIS 218 Advanced UNIX 85

6.5. trap

 Capture user interrupts or system call failures.  Format (with ’): trap ’commands’ signal-numbers-or-name  Some signal numbers (names):

– 2 (INT) press delete or control-C – 3 (QUIT) press control-| or control-\ – 15 (TERM) kill command signal

continued

CIS 218 Advanced UNIX 86

 A complete list of available signals is

given by typing trap -l at the command line.

 To ignore a signal, set the trap command

to be empty (’’)

 To reset signal processing, set the

command to -

continued

CIS 218 Advanced UNIX 87

 $ cat inter

trap ’echo PROGRAM INTERRUPTED; exit 1’ INT while true do echo Program running. sleep 2 done

CIS 218 Advanced UNIX 88

• 7. Functions

 Bash allows shell scripts to use functions: function_name() { statements }  Functions must be defined textually before

they are used.

continued

CIS 218 Advanced UNIX 89

 Functions can return integer values  Function parameters are passed by

modifying $*, $@, $#, $1 -- $9 while the function is executing.

 Local variables are defined with the local

keyword

– the other variables in a script are global by default

CIS 218 Advanced UNIX 90

my_name

 #!/bin/sh

yes_or_no() { # a function echo "Is your name $* ?" while true do echo -n "Enter yes or no: " read x case "$x" in y | yes ) return 0;; n | no ) return 1;; * ) echo "Answer yes or no" esac done } # end of yes_or_no()

continued

CIS 218 Advanced UNIX 91

# the main part of the script echo "Original parameters are $*" if yes_or_no "$1" then echo "Hi $1, nice name" else echo "Never mind" fi exit 0

CIS 218 Advanced UNIX 92

Use

 $ my_name andrew davison

Original parameters are andrew davison Is your name andrew ? Enter yes or no: y Hi andrew, nice name $

CIS 218 Advanced UNIX 93

• 8. Useful Scripting Commands

 expr evaluates its argument as an

expression:

ans=‘expr $x + 1‘  The usually operators are available:

– + - * / (integer divison) % (modulo) – > >= < <= – = (equality) != – | (or) & (and)

continued

CIS 218 Advanced UNIX 94

 Bash supports printf, as a more flexible echo – printf "format string" parameter1 ...  Very similar to printf() in C

– main restriction is no support for floats – only integers are supported in the shell

 $ printf "%s %d\t%s\n" "hi there" 15 students

hi there 15 students $

printf

CIS 218 Advanced UNIX 95

• 9. Here Documents

 A here document allows input to be passed

into a command from within a script

– the command thinks the input is coming from a file or input stream

 A here document begins with <<LABEL, and

ends with LABEL

– LABEL can be anything

CIS 218 Advanced UNIX 96

 $ cat here1

#!/bin/sh cat <<!FUNKY! hello this is a here document !FUNKY!

 $ here1

hello this is a here document $

the here document

CIS 218 Advanced UNIX 97

• 10. Debugging

 Various options can be set when invoking a

shell script to help with debugging.

 There are two ways to set the options:

– from the command line when calling the script – from within the script by using set

continued

CIS 218 Advanced UNIX 98

Command Line Set

 sh -n script

set -n

– do not execute the script, only parse it

 sh -v script

set -v

– echoes commands after executing them

 sh -x script

set -u

– warns when an undefined variable is used

CIS 218 Advanced UNIX 99

• 11. More Information

 The Bourne Shell:

– Ch. 10, Sobell

 Bourne/Bash:

– Beginning Linux Programming Neil Matthew and Rick Stones Chapter 2