Teacher's Notes - Lab Chapter 3 - Basic Commands and Scripting

7/21/2019 Teacher's Notes - Lab Chapter 3 - Basic Commands and Scripting

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J.E.D.I.

1 Basic commands and Scripting

1.1 ObjectivesThe objective of this chapter is to teach basic knowledge of the Solaris terminal and createbasic bash scripts.

1.2 Chapter Outline● Terminal

● Help commands

● Navigating the file sstem

●

!odifing the file sstem● "edirecting o#tp#t

● Environment variables

● $asic Scripts

● %dvanced Scripting

● %dministration

1.3 The terminal

&earning an operating sstem goes beond knowledge of the graphical #ser interface. Thegraphical #ser interface is eno#gh for reg#lar #ser. The terminal allows for the e'ec#tion ofpowerf#l commands. This chapter teaches some of the basic commands of the Solaris terminalas well as gives an introd#ction to shell scripting.

(o# can open a terminal b right)clicking on the desktop and selecting *pen Terminal.

The prompt is where terminal commands are entered. +or o#r e'ample, we will represent theterminal command with a - sign. (o# do not have to tpe the - sign when o# are enteringcommands.

In a later part of this chapter, o# will be asked to switch to the root #ser. The root #ser, alsoknown as the s#per#ser, is the administrator of o#r comp#ter, with access to commandswhich have sstemwide effect. The terminal prompt for the s#per#ser changes to reflect this,

and to represent the s#per#ser, we will #se the sign. (o# do not have to tpe the signwhen entering commands.

/ommands as well as filenames in Solaris are case sensitive. "#nning the ls command, fore'ample, as &S or &s will not e'ec#te the ls command at all.

1.4 Help commandsEach terminal command in Solaris comes with help doc#mentation. (o# can access this br#nning the man command followed b the command that o# wo#ld like to ask help on. +ore'ample, to ask help on the ls command, simpl tpe.

$ man ls

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(o# can navigate thro#gh the man#al #sing the #p and down kes. To 1#it, o# can press 1.

Some commands come with their own help o#tp#t. Invoking this varies per command.

1. !avigating the "ile s#stem

1.5.1 ls command

The ls command lists files in o#r c#rrent director. If o# r#n ls now, it will show o# the filesin o#r home director.

(o# can also view selected files #sing ls. If the file is not there, then the command does notprod#ce an o#tp#t.

The ls command can be #sed with wildcards. 2sing ls with wildcards allows o# to view filesthat match a certain criteria. The following are the commonl #sed wildcards

● 3 ) represents 4 or more characters. +or e'ample, ls a3 will list all files which begin withthe letter a. ls 3.java lists down all files that end with .java, or all java files. ls 3 listsdown all files, which is also its defa#lt behavior.

● 5 ) represents a single character. +or e'ample, ls 5a5 will match all files which has an a

in the middle

%s with most commands, ls can be given additional options, specified b the min#s sign. +ore'ample, to view files in long format, which shows additional file information, o# can #se the)l option. To view all files 6incl#ding hidden files7 o# can #se the )a option. To do both, o#can tpe ls )a )l, or better, ls )al.

"#nning the ls command with the )a option lists down hidden files. Hidden files are filenamesthat begin with a period. +or e'ample, the .bashrc script is a hidden file that r#ns whenever aterminal is opened. (o# can also create hidden files simpl b #sing a period at the start ofo#r file

Some options consist of words instead of single letters. Some options ma also re1#ire someparameters, which are often specified with an e1#al statement. See the following e'ample,which lists down all files, and the additional )sort option, with the parameter si8e which viewsall files according to si8e.

$ ls -al –sort=size

There are man other options for the ls command which o# can check o#t b viewing the manpage.

1.5.2 File permissions

% short description of the o#tp#t of ls )l is necessar at this point. In partic#lar, we will disc#ssfile permissions.

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The first blank in the access control list describes what tpe of file is being listed. Having ablank there means that it is a reg#lar file. % d indicates a director, an l or s indicates a hard orsoft link to another file respectivel. +or devices, b indicates that the file represents a blockdevice while c indicates that the file points to a character device.

There are three possible permissions. +or a file to be readable, it m#st have the r permission.If a #ser wishes to change the file, then the #ser m#st have the w permission. If the file can bee'ec#ted, then the #ser e'ec#ting the file m#st have the ' permission.

The access control list is divided into three parts. The first three characters is the #serpermission list indicating if the #ser can read, write or e'ec#te the file. The ne't threecharacters is the gro#p access permission while the final three letters indicate the permissionof non)gro#p members.

/onsider the following access permission: rw'rw)r))

The first three letters determine the #ser permission. Having r there means that the file isreadable b the file creator. The w means that the file can be written 6its not read)onl7. The '

permission means that the file is e'ec#table. +or o#r e'ample, the #ser can read, write ande'ec#te the file.

2sers in 2NI; sstems can belong to #ser gro#ps, and the ne't three characters determinewhat permissions other people in the same gro#p as the file creator can do. % missingpermission 6in this case, the ' permission7 means that the other gro#p members cannotperform that operation on the file 6i.e. *ther gro#p members cannot e'ec#te this file7.

+inall, the last three characters stand for the permissions of people belonging to other gro#ps.%s can be seen, with the w and ' permissions blanked o#t, other sstem #sers can onl readthe file.

+ile permissions can be changed with the chmod command. The chmod command accepts twoparameters, the filename of the file o# want changed, and the new permissions specified#sing three octal digits.

If an octal digit is converted into binar, then the binar n#mber wo#ld consist of three digits.+or the access control list, 0 means that permission wo#ld be set, 4 means that thatpermission will not be given. /hmod needs three octal digits, the first digit for the #serpermissions, the second for the gro#p permissions, and the third for the permissions for other#sers.

+or e'ample, if we have a file called hello.t't, the permission rw'rw)r co#ld be set b chmod<=> hello.t't 6000 004 0447. ?ermission rw)r)'r)) co#ld be set b chmod =@> hello.t't 6004040 0447.

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1.5.3 cd and pwd command

%s was mentioned earlier, o# are c#rrentl in o#r home director. To find o#t what o#rc#rrent director is, o# can r#n the pwd command, which stands for present workingdirector.

$ pwd/export/home/alice

The Solaris file sstem starts from the root director, or the B director. To get to o#r homedirector from the root director, o# first have to go to the e'ports director, then to thehome director #nder that, and then finall to the director with the same name as o#r #sername.

(o# ma change o#r director with the cd command, followed b the name of the directorthat o# want to go to. Since there arenCt an directories in the home director, let #s first goto the root director 6B7 as shown b the following command.

$ cd /

If o# r#n the ls command there, o# will be shown the top level director of the lin#' filesstem. The following diagram shows a tpical file sstem for 2NI; based sstems like Solaris.

To go to, for e'ample, the etc director, again o# can r#n the cd command, followed b thedirector o# want to go to

$ cd etc

If o# r#n pwd again, it will show that indeed, o# are in the etc director. (o# can go into the

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s#bdirectories of etc if o# wish to view the files that are there.

To go #p one step, o# can tpe the following command

$ cd ..

The do#ble period is a reference to the parent director of the c#rrent director. Th#s, if o#were in the etc director, then o# wo#ld go back one step #p to the root director. The singleperiod is #sed to specif the c#rrent director 6we shall #se this later with other commands7

There are two was to specif a director. (o# can specif the relative director name as wedid with etc. (o# can specif more than one director. +or e'ample, to go from the rootdirector to the defa#lts director in the etc director, o# can sa

$ cd etc/defaults

(o# can also specif the absol#te director name. The absol#te director name is the completename of the director path starting from the root director. +or e'ample, from an director in

o#r sstem, o# can go back to o#r home director via the command$ cd /export/home/<username>

If o#r #sername is alice, then o#r command wo#ld be

$ cd /export/home/alice

In addition, simpl tping cd will place o# directl in the home director.

1.5.4 The Solaris file system

%s we have beg#n navigating the file sstem, we shall ret#rn to the root director and listdown the directories of the Solaris sstem. %ltho#gh there are man directories, and thesedirectories ma change depending on o#r installation, the following are the commondirectories and their #se

● Be'portBhome The home director of all #sers in the sstem. Some machines ma

have this as the Bhome director

● B#sr The e'ec#table files of o#r Solaris sstem

● Betc /onfig#ration files are stored here

● Bvar ariable director. This is where temporar files s#ch as logs are stored

● Bproc % special director of o#r file sstem which displas the applications c#rrentl

r#nning in o#r sstem as files

● Bmnt Directories where removable media, s#ch as flopps, /Ds, and flash disks are

mo#nted.

● Bdev devices are represented as files in Solaris and placed in this director.

1.5.5 du and df

The d# 6or disk #sage7 command lists down how m#ch space is being #sed b files in aspecified director, incl#ding s#b)directories. It is often #se with the )h command, to give a

h#man readable o#tp#t.$ du -h /etc

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5K /etc/certs

5K /etc/cron.d

5K /etc/crypto/certs

K /etc/crypto/crls

K /etc/crypto

!"K /etc/default "K /etc/de#ices

...

5! /etc

The df command stands for disk free. "#nning df displas #sage statistics for all disks in thesstem. &ike d# it is #sed with )h which gives h#man readable o#tp#t

$ df -h

%ilesystem size used a#ail capacity ounted on

/de#/ds&/c't'd's' "( ".)( *."( "'+ /

/de#ices 'K 'K 'K '+ /de#ices

ctfs 'K 'K 'K '+ /system/contract

proc 'K 'K 'K '+ /procmntta, 'K 'K 'K '+ /etc/mntta,

swap .( . .( + /etc/s#c/#olatile

o,fs 'K 'K 'K '+ /system/o,ect

fd 'K 'K 'K '+ /de#/fd

swap .( 'K .( '+ /tmp

swap .( )K .( + /#ar/run

/de#/ds&/c't'd's0 *( ).( ( "+ /export/home

1.5.6 The find command

To look for a file, o# can #se the file command. The find command starts looking for afilename 6specified b the )name option7 from the given director, rec#rsivel looking thro#gh

all the s#bdirectories. (o# can even #se wildcards with this command.+or e'ample, we look for all files in the Betc director that start with the word profile

$ find /etc -name profile1

%gain, there are man other options with the find command which o# can read #p on #singthe man command.

1.$ %odi"#ing the "ile s#stemNote that at this stage o# can onl make changes to o#r home director. *nl the root #sercan perform changes to other directories in the sstem.

1.6.1 File copying

(o# can cop files with the cp command. The cp command has two arg#ments, the so#rce fileand the destination file. Note that these filenames can contain directories as well as wildcards.

+or e'ample, if o# want to cop the passwd file in the Betc director to o#r c#rrent director,o# can sa

$ cp /etc/passwd .

If o# want to cop all files in the Betc director to o#r home director, o# can sa

$ cp /etc/1 /export/home/<username>

If the destination is a filename and not a director, then the cp command copies the file and

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renames it. +or e'ample, if o# have a te't file named a.t't and o# want to make a cop of itinto a file named b.t't, o# can sa

$ cp a.txt ,.txt

(o# ma cop entire directories b #sing the )r option, which stands for rec#rsive coping."ec#rsive coping incl#des even s#bdirectories of the specified so#rce director. +or e'ample,if o# want to cop all of the contents of Betc to o#r home director, then o# can sa

$ cp -r /etc /export/home/<username>

*nce the coping has finished, o# can take a look at o#r home director and see a new etcdirector there.

To move files, o# can #se the mv command. The mv command has similar options andf#nctionalit as the cp command, e'cept that it deletes the so#rce after the file6s7 ordirectories have been moved.

+or e'ample, we move o#r a.t't to c.t't

$ m# a.txt c.txt

Deleting files j#st accepts a single parameter, the file that o# want to delete. +or e'ample, ifwe want to delete c.t't, we can sa

$ rm c.txt

rm can also accept m#ltiple files, as in

$ rm file file

rm can be #sed with wildcards. +or e'ample, the following deletes all files in, for e'ample, atemporar director in o#r home folder.

$ rm /export/home/<username>/temp/1

Note that this deletes onl files. Director deletion will be disc#ssed later.

1.6.2 Directory creation and deletion

To create directories, o# can #se the mkdir command. +or e'ample, to create a directornamed lesson0, o# can sa

$ m&dir lesson

This creates a new s#bdirector in o#r c#rrent director. (o# ma also specif a complete

path from the root. +or e'ample, what if o# want to make an e'ercise0 director insidelesson0:

$ m&dir /export/home/<username>/lesson/exercise

To delete directories, o# can #se the rmdir command. The rmdir command can accept arelative pathname or an absol#te pathname. +or e'ample, if o# want to delete the e'ercise0director, o# can sa

$ rmdir /export/home/<username>/lesson/exercise

Note that the rmdir command can onl work if the director is alread empt of files, so o#ma need to #se the rm command there first to remove all files, and rmdir to remove alldirectories before o# are able to delete that director.

However, there is a shortc#t to this. (o# can #se the rm command with the option )rf, )r for

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rec#rsive 6which means delete even s#bdirectories7, and )f for forced deletion. The followinge'ample deletes the lesson0 director even if it has content inside it.

$ rm -rf /export/home/<username>/lesson

Note that this is a ver dangero#s command. If o# are in the root director and sa rm )rf .,o# wo#ld end #p deleting the entire file sstem. Note that there is no eas wa to #ndeletefiles in Solaris, as s#ch, proceed with ca#tion when #sing this command.

1.& 'iping output to a program or "ile

1..1 !edirections

The o#tp#t of commands can be redirected to a file. +or e'ample, listing the contents of the Betc command ma fill the entire screen, so perhaps o# wo#ld like to have this saved into afile for viewing with a te't editor later. To do this, simpl place the F operand after thecommand and indicate the filename where the o#tp#t is to be saved.

$ ls -l /etc > list.txt

*nce the e'ec#tion is done, o# can view the o#tp#t of the file via an te't editor or to save itfor later analsis. This redirection can be made to work with an command.

The F operand overwrites the old contents of the destination file. To append o#tp#t to a file,o# can #se the FF operand. +or e'ample, if we want to add more files to o#r list.t't, we canwrite:

$ ls -l /usr >> list.txt

The append command is often #sed for logging, where the o#tp#t of a program, s#ch asoperating sstem messages, is stored over a long period of time.

%s a final note, we have a command called echo which simpl prints o#t what the parameterwas passed in. +or e'ample:

$ echo 23ello world42

3ello world4

(o# can redirect the echo command to add some organi8ation to o#r logs. +or e'ample:

$ echo 2istin6 the contents of /etc2 > list.txt

$ ls -l /etc >> list.txt

$ echo 2istin6 the contents of /usr2 >> list.txt

$ ls -l /usr >> list.txt

If o# want to totall s#ppress the o#tp#t of a command, o# can redirect it to a special filecalled BdevBn#ll. This is a special file that simpl discards an o#tp#t sent to it.

*#tp#t s#ppression co#ld be #sed to change the wa a program behaves. GeCll see thise'ample later on.

+or e'ample, the following command totall s#ppresses o#tp#t of the ls command$ ls /etc > /de#/null > /de#/null

1..2 "rror streams

2NI; sstems differentiate between o#tp#t stream and an error stream. *#tp#t stream is o#rreg#lar o#tp#t while the error stream is for program errors.

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?rogramming lang#ages often provide commands to send information to the error stream. Javaprovides two different o#tp#t commands. Sstem.o#t.println67 for reg#lar o#tp#t andSstem.err.println67 for error o#tp#t

(o# can see the error stream at work if o# r#n the following command:

$ ls nosuchfile.txt > output.txtls7 nosuchfile.txt7 8o such file found

The ls error is sent to the error stream, not to o#tp#t.t't

The F operand redirects onl the o#tp#t stream

If o# want to redirect the error stream as well, o# can #se the 9F operand

$ ls nosuchfile.txt > output.txt > error.txt

1..3 #sing more and less

(o# can also #se the more command to view the contents on the screen. The more command

pa#ses the o#tp#t so o# can view one screenf#l at a time. (o# chain the more command withls #sing the pipe 67 command.

$ ls -l /etc 9 more

The more command, however, is limited to onl forward movement. The less command, similarto more, allows for backward and forward viewing of the o#tp#t, 6i.e. &ess is more7

$ ls -l /etc 9 less

1.( )nvironment variablesEnvironment variables are variables that are defined b the operating sstem. ariables areidentified b the - sign in front of them. +or e'ample, the -?%TH variable lists down thedirectories that the terminal looks for e'ec#table files when the #ser r#ns a command. To findo#t the val#e of o#r path variable, o# can sa

$ echo $:;3

*ther e'amples of environment variables are the -H*!E, -2SE", and -?GD which show o#rhome director, c#rrent #ser name and present working director respectivel. (o# can find o#ttheir val#es b r#nning the echo command. The following echo command shows these val#esas well as show how o# can mi' string messages with variables in a single echo command.

$ echo 23ello4 y username is 2 $?@ 2. A call the 2 $3B? 2 directory as

my home.2

Hello m #sername is alice. I call the Be'portBhomeBalice director as m home.

(o# can #se both single and do#ble 1#otes in the echo command. The difference is that placinga variable inside a do#ble 1#ote wo#ld e'pand the val#e of the variable.

$ echo 23ello4 y name is $?@2

3ello4 y name is $?@

$ echo C3ello4 y name is $?@C

3ello4 y name is alice.

%s can be seen, placing the - sign in do#ble)1#oted echo means that the word after it will beconsidered as a variable. To be able to print the - sign, simpl p#t a backslash in front of the -sign 6i.e. K-7.

(o# can also define o#r own variables. +or e'ample, o# want to have o#r own #ser defined

greeting, o# can sa at the prompt:

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$ 6reetin6=2Duenos dias42

Note that o# donCt have to p#t the - sign if o#Cre assigning a val#e to a variable 6the -shown there is the prompt7. %lso, there sho#ld not be spaces between both sides of theassignment operator. ariable names are also case sensitive.

(o# can now #se o#r variable as o# wo#ld the other environment variables.

$ echo $6reetin6 2 y username is 2 $?@ 2. A call the 2 $3B? 2

directory as my home.2

Duenos dias4 y username is alice. A call the /export/home/alice directory

as my home.

(o# can also change the val#e of e'isting variables. +or instance, if o# want to add o#r homedirector to the path variable to alwas look in o#r home director, o# can sa:

$ :;3=$:;37/export/home/<username>

Note that #ser)defined variables are accessible onl within the terminal where the are

declared. If o# have other open terminal windows, the will be #nable to access o#r #serdefined variable. %lso, once o# close o#r terminal, the variableCs val#e will disappear.

&ater on we will learn how to permanentl store a #ser)defined variable.

1.* Basic Scripts(o# can consider a script to be a file that contains s#ccessive instr#ctions for the terminal.Some sstem tasks involve a s#ccessive chain of simple commands, b placing these in ascript, o#Cll save o#rself some time and effort b e'ec#ting onl a single command.

Scripting also goes beond j#st a chain of commands, most scripting lang#ages have their ownprogramming constr#cts s#ch as if)statements and loops, and can accept #ser inp#t. Ge will

disc#ss basic and advanced scripting in this chapter.

+or this chapter, we will #se the bash scripting lang#age. $ash stands for $o#rne)again shell,which is a revision of the original $o#rne shell. There are other shells, s#ch as ksh or kornshell, or c shell 6csh7, each with different snta'. However, the lessons learned here are easilapplicable to the other shells.

1.$.1 %reating a &ash script

In o#r previo#s e'ample where we listed down the contents of o#r Betc and B#sr directoriesand placed them in a file called list.t't. $elow is a basic script file that chains these instr#ctionstogether. (o# can #se an te't editor to write this file down. Ge will name o#r file as mscript.

E4/,in/,ash

E this is my first ,ash script.

echo 2istin6 the contents of /etc2 > list.txt

ls -l /etc >> list.txt

echo 2istin6 the contents of /usr2 >> list.txt

ls -l /usr >> list.txt

/omments are preceeded b a sign. However, the first line of o#r script indicates that thisscript is to be r#n with bash, whose e'ec#table file is in the director Bbin.

To e'ec#te this file, we m#st first change its file permissions. To find o#t what o#r scriptCs file

permissions, we can #se the ls )l command.

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$ ls -l myscript

-rw-r--r-- alice alice ! 8o# )7' myscript

The file permissions for mscript are read)writable for the file owner alice and onl readable forall others. To make o#r script e'ec#table, we simpl add the e'ec#table permission to it #singthe chmod command

$ chmod 055 myscript

$ ls -l myscript

-rwxr-xr-x alice alice ! 8o# )7 myscript

Now all #sers have permission to e'ec#te mscript.

To r#n o#r script, we simpl sa

- .Bmscript

1.$.2 %omments

/omments in a bash script start with a . There sho#ld be a space between the and the firstletter of o#r comment

The first line of the bash script is not reall a comment b#t an indicator on which scriptinglang#age to e'ec#te the script on:

● MBbinBbash tells the *S to #se bash to r#n this script

● MBbinBksh tells the *S to #se another scripting lang#age 6korn shell7 to r#n the script

1.$.3 'uilt(in &ash scripts

!ost 2NI; based sstems e'tensivel #sed scripts for sstem e'ec#tion. +or e'ample, whenbash first starts on boot #p, it e'ec#tes commands from the script file BetcBprofile. The ?%THvariable among others, is set here.

*n #ser log)in goes to the home director and reads the hidden files .bashprofile, .bashloginand .profile and e'ec#tes those scripts.

Ghen a terminal is started, it e'ec#tes commands from the .bashrc script of the c#rrent #ser.

Ghen a login shell e'its, $ash reads and e'ec#tes commands from the file .bashlogo#t

1.1+ ,dvanced ScriptingIn this section, we will disc#ss how to #sed variables, decision statements and loopingstatements in scripts. Ge will also disc#ss positional inp#t.

1.1).1 *aria&le su&stitution

%s was disc#ssed previo#sl, a bash variable is indicated with a - sign. In realit, the - is acommand that indicates that the val#e of a variable is to be s#bstit#ted at that position whenthe command is r#n.

+or e'ample consider the following commands

$ x=$ echo $x

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*#r variable ' contains the val#e >9. The command echo -' is internall s#bstit#ted as echo>9. %s most of the time we do #se variables in this manner, we onl need to remember thatthe onl time the - does not appear is d#ring variable assignment and when a variable isE;?*"Ted.

This s#bstit#tion can be seen with the newline character. J#st like in most programminglang#ages, a newline can be printed with a backslash n 6i.e. Kn7 However, placing Kn in an echostring does not prod#ce a newline. The wa to do this is to #se a -CKnC. This s#bstit#tes anewline at the position where the backslash n appears

$ echo 2hello Fn world2

hello Fn world

$ echo 2hello2 $2Fn2 2world2

3ello

world

(o# can even #se variables to store the o#tp#t of some programs b encloseing the commandin tick marks O O. +or e'ample, the following script file stores the o#tp#t of ls Betc to a variableand o#tp#ts it.

E4/,in/,ash

x=Gls /etcG

echo CBur #aria,le contains the followin6 filesC

echo $x

1.1+.1.1 -egular variables

ariables in script files are declared in the #s#al wa. However, the are not visible o#tside ofthe script file #nless the are E;?*"Ted. +or e'ample, o# can view the BetcBprofile script filewhich E;?*"Ts the path variable.

1.1+.1.2 'ositional variables "or user input

Special variables -0, -9 to -L s#bstit#te for arg#ments to the script file. %rg#ments areadditional words separated b spaces in addition to the command that r#ns the script file. Thisis one of the was to have #ser inp#t in a script file. /onsider the following script, which we willsave in a file called argtest. The n#mber of arg#ments passed into the script is represented bthe variable -.

E4/,in/,ash

echo 2y first ar6ument2 $

echo 2y second ar6ument2 $

echo 28um,er of ar6uments passed2 $E

The following wo#ld be the o#tp#ts of argtest on certain arg#ments.

$ ./ar6test

y first ar6ument

y second ar6ument

8um,er of ar6uments passed '

$ ./ar6test hello

y first ar6ument hello

y second ar6ument

8um,er of ar6uments passed

$ ./ar6test hello world star

y first ar6ument hello

y second ar6ument world8um,er of ar6uments passed "

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+or positional variables above -L, the val#e m#st be placed inside brackets 6i.e. -P04Q, -P00Qand so on7.

1.1).2 !ead command (o# can also have inp#t to o#r script file with the read command. +or e'ample, the followingscript file asks for a name

E4/,in/,ash

echo C?nter nameC

read n

echo C3elloHC $n C4C

1.1).3 "rror %odes

%ll commands in most 2NI; sstems have an error code. Error code val#e ranges from 4 to9@@. $ convention, a program that ret#rns 4 after it e'ec#tes has r#n s#ccessf#ll. %n otherval#e is a false val#e

(o# can find o#t the error code of the last e'ec#ted command in bash via the -5 variable.

+or e'ample, the following script file o#tp#ts the error code of ls after searching a specified file.

E4/,in/,ash

ls $

echo 2he errorcode of ls command is7 2 $I

The following is its sample o#tp#t 6if o# save the file as lstest7

$ ./lstest

<list of files>he errorcode of ls command is7 '

$ ./lstest nosuchfile.txt

8o such file or directory

he errorcode of ls command is7

(o# can specif the error code of o#r script with the e'it command. +or e'ample, at the endof the lstest script, we can ret#rn for o#r error code the error code of ls. Note that we have tosave the val#e of -5 to another variable. Ge do this as -5 ret#rns the error code of the lastcommand r#n. If we did not modif it, it wo#ld ret#rn the error code of echo

E4/,in/,ash

ls $

output=$I

echo 2he errorcode of ls command is7 2 $output

exit $output

1.1).4 +perators

%rithmetic operators are still the #s#al R, ), 3 or B. The operator ret#rns the remainder ofinteger division.

The res#lt of an arithmetic e'pression can be assigned to a variable #sing the let command.+or e'ample:

$ x=5

$ let Cx = $x J C$ echo $x

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!

(o# ma also #se the 66 ... 77 command, which eval#ates the e'pression inside the do#bleparenthesis. Note that a - m#st be placed before the 66 for a val#e s#bstit#tion to occ#r.

$ x=$5 J 5LL

$ echo $x'

2nfort#natel, bash does not #nderstand floating)point n#mbers and treats n#mbers with adecimal point as strings.

1.1).5 %onditional Statements

In bash, 4 is for tr#e, 0 is for false. This reflects the val#e ret#rned b all commands in Solaris.$ convention, a program that ret#rns a 4 after it e'ec#tes is a program that r#ns s#ccessf#ll,0 otherwise.

(o# can test for a condition #sing an if)statement. Similar to programing lang#ages, there isthe if statement, the if)else statement and the if)elseif)else statement. The following is thesnta' of the if)elseif)else statement

if M condition N

then

<statements>

elif M condition N

then

<statements>

else

<statements>

fi

The condition part of o#r if statements consist of the following. Note that -a and -b can bevariables or act#al val#es.

● if -a )e1 -b U ) N#merical e1#alit

● if -a V -b U ) String e1#alit

● if -a )ne -b U ) N#merical ine1#alit

● if -a MV -b U ) String ine1#alit

● )gt, )ge, )lt, )le n#merical greater)than, greater)than)e1#al)to, less)than, less)than)

e1#al)to

● )n, )8 not n#ll or n#ll string comparison. +or e'ample, if )n -0 U means if the first

arg#ment is not n#ll.

● if Wcondition0F U XX Wcondition9F U ) and operation

● if Wcondition0F U Wcondition9F U ) or operation

● if M WconditionF U ) not operation. +or e'ample, if M -a )gt -b U means if not a is

greater than b

● )f if the specified filename e'ists. +or e'ample if )f hello.t't U checks if the filehello.t't is valid

● )r, )w, )' checks if the filename has read, write, or e'ec#te privileges respectivel

+or e'ample, recall o#r mscript e'ample. Ge can pass as an arg#ment the filename that wewo#ld like to save the contents of Betc and B#sr to. If no arg#ment was passed, 6i.e. -0 is n#ll7,

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then we will o#tp#t an error.

E4/,in/,ash

E this is my first ,ash script.

if M -n $ N

then

echo 2istin6 the contents of /etc2 > $ls -l /etc >> $

echo 2istin6 the contents of /usr2 >> $

ls -l /usr >> $

else

echo 2Oou should specify a parameter2

fi

1.1).6 ,oops

There are two constr#cts for loopsing, the for loop and the while loop.

1.1+.$.1 or loopThe snta' of the for loop looks like this:

for var in list

do

WstatementsF

done

&ist is a list of val#es var takes on. +or the first pass, var takes on the first element in the list,the second pass, var takes on the second val#e, and so on.

+or e'ample the following for loop lists down the das of the week.

for days in ConC CuesC CPedC ChursC C%riC CatC CunC

do

echo $days

done

1.1+.$.2 /hile loop

The while loop tests for a condition and keeps on looping while the condition is tr#e. Its snta'is:

while condition U

do

WstatementsF

done

+or e'ample, the following loop prints o#t hello world given a specified arg#ment.

E4/,in/,ash

y='

while M $y -l $ N

do

echo 2hello world2

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let Cy = y J C

done

1.11 Basic ,dministration Commands

1.11.1 Switching to root

Sstem administration can be done b the s#per #ser or root #ser. +or instance, editing of theconfig#ration files in Betc, s#ch as the profile script file, can onl be done as root. To access theroot acco#nt, o# can log)in as root, or #se the switch #ser command.

$ su

?nter password7 1111111

E

Note how the prompt has changed to reflect the s#per #ser stat#s. The s# command can alsobe #sed to change to a specified acco#nt.

$ su ,o,

?nter password7 1111111

$ <-- currently lo66ed in as user ,o,L

1.11.2 #ser administration

The following are some basic commands that the root #ser can #se to administer the sstem

To add #sers in Solaris, o# can #se the #seradd command+or e'ample, the following command adds #ser alice

E useradd -d /export/home/alice -m -s /,in/,ash alice

The additional options are as follows● )d specifies the home director for the #ser. This sho#ld be set#p in Be'portBhome

● )m tells #seradd to man#all create the director

● )s specifies the terminal shell to be #sed b alice, in this case, bash

To change the password of a #ser, o# can r#n the passwd command. +or e'ample, to changethe password of alice r#n:

E passwd alice

If no parameter is given, this changes the password of the c#rrent #ser. This form can also be#sed b non)root #sers to change their passwords.

To delete #sers, o# can r#n the #serdel command. +or e'ample, to delete #ser alice● E userdel -r alice

● )r specifies to remove the #ser director as well

● #seradd W#sernameF ) creates a new #ser with the specified #sername

● #serdel W#sernameF ) deletes a #ser

● passwd W#sernameF ) changes the password of a given #ser. If no parameter is given,

this changes the password of the c#rrent #ser. This form can also be #sed b non)root

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#sers to change their passwords.

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Teacher's Notes - Lab Chapter 3 - Basic Commands and Scripting

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