2. Basic Commands of Unix

8/16/2019 2. Basic Commands of Unix

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2. Basic commands ofUnix

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Unix - File Management All data in UNIX is organized into les. All les are

organized into directories. Tese directories are

organized into a tree-li!e str"ct"re called teles#stem. $en #o" %or! %it UNIX& one %a# or anoter #o"

s'end most of #o"r time %or!ing %it les. Tis lesson

%o"ld teac #o" o% to create and remo(e les& co'#and rename tem& create lin!s to tem etc. In UNIX tere are tree )asic t#'es of les *

Ordinary Files * An ordinar# le is a le on te s#stem tatcontains data& text& or 'rogram instr"ctions

Directories * +irectories store )ot s'ecial and ordinar# les.For "sers familiar %it $indo%s or Mac ,& UNIX directories aree"i(alent to folders.

Special Files * ome s'ecial les 'ro(ide access to ard%ares"c as ard dri(es& /+-0,M dri(es& modems& and ternet

ada'ters. ,ter s'ecial les are similar to aliases or sortc"tsand ena)le o" to access a sin le le "sin dierent names

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3isting Files To list te les and directories stored in te

c"rrent director#. Use te follo%ing command$ls

4ere is te sam'le o"t'"t of te a)o(ecommand *

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3isting Files Te command ls s"''orts te -l o'tion %ic %o"ld

el' #o" to get more information a)o"t te listed les

*

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col"mns First Column: re'resents le t#'e and

'ermission gi(en on te le. Belo% is te

descri'tion of all t#'e of les. Second Column: re'resents te n"m)er of

memor# )loc!s ta!en )# te le or director#.

Third Column: re'resents o%ner of te le. Tis is te Unix "ser %o created tis le.

Fourth Column7 re'resents gro"' of teo%ner. (er# Unix "ser %o"ld a(e an

associated gro"'. Fifth Column: re'resents le size in )#tes. Sixth Column: re'resents date and time %en

tis le %as created or modied last time.

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te t#'e of le tat9s listed In te ls -l listing exam'le& e(er# le line )egan %it a

d& -& or l. Tese caracters indicate te t#'e of le tat9s

listed.

:

;rex +escri'tion

-0eg"lar le& s"c as an A/II text le& )inar#exec"ta)le& or ard lin!.

bBloc! s'ecial le. Bloc! in'"t


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Meta /aracters Meta caracters a(e s'ecial meaning in Unix. For

exam'le = and > are metacaracters. $e "se = to matc

? or more caracters& a "estion mar! > matces %itsingle caracter. For xam'le *

+is'la#s all te les %ose name start %it c and ends%it .doc

4ere = %or!s as meta caracter %ic matces %itan# caracter. If #o" %ant to dis'la# all te les ending

%it @"st .doc ten #o" can "se follo%ing command *


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4idden Files An in(isi)le le is one %ose rst caracter is

te dot or 'eriod caracter .C. UNIX 'rogramsincl"ding te sellC "se most of tese les tostore cong"ration information.

ome common exam'les of idden les incl"de

te les * .'role * te Bo"rne sell sC initialization

scri't .!src * te Dorn sell !sC initialization

scri't .csrc * te / sell csC initialization scri't .rosts * te remote sell cong"ration le

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To list in(isi)le les To list in(isi)le les& s'ecif# te -a o'tion to ls

ingle dot . * Tis re'resents c"rrent director#. +o")le dot .. * Tis re'resents 'arent director#.

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F es Go" can edit an existing le "sing (i editor. #o" can

o'en existing le as follo%s

,nce le is o'ened& #o" can come in edit mode )#'ressing !e# i and ten #o" can edit le as #o" li!e. If#o" %ant to mo(e ere and tere inside a le ten rst#o" need to come o"t of edit mode )# 'ressing !e# esc

and ten #o" can "se follo%ing !e#s to mo(e inside ale * l !e# to mo(e to te rigt side. h !e# to mo(e to te left side.

k !e# to mo(e "' side in te le. j !e# to mo(e do%n side in te le.

o "sing a)o(e !e#s #o" can 'osition #o"r c"rsor %eree(er #o" %ant to edit. ,nce #o" are 'ositioned ten#o" can "se i !e# to come in edit mode. dit te le&once #o" are done 'ress esc and nall# t%o !e#s Shift1?


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+is'la# /ontent of a File Go" can "se cat command to see te content of a le.

Follo%ing is te sim'le exam'le to see te content of

a)o(e created le

Go" can dis'la# line n"m)ers )# "sing -b o'tion along%it cat command as follo%s

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/o"nting $ords in a File Go" can "se te wc command to get a co"nt of te total

n"m)er of lines& %ords& and caracters contained in ale. Follo%ing is te sim'le exam'le to see teinformation a)o"t a)o(e created le *

4ere is te detail of all te fo"r col"mns * First /ol"mn7 re'resents total n"m)er of lines in te

le. econd /ol"mn7 re'resents total n"m)er of %ords in

te le. Tird /ol"mn7 re'resents total n"m)er of )#tes in

te le. Tis is act"al size of te le. Fo"rt /ol"mn7 re'resents le name. 12


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/o'#ing Files To ma!e a co'# of a le "se te c' command.

Te )asic s#ntax of te command is *$ cp source_file destination_file

Follo%ing is te exam'le to create a co'# ofexisting le lename.

$ cp filename copyfile

$ No% #o" %o"ld nd one more le co'#le in

#o"r c"rrent director#. Tis le %o"ld )e exactl#same as original le lename.

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0enaming Files To cange te name of a le "se te m(

command. Its )asic s#ntax is:$ mv old_file new_file

Follo%ing is te exam'le %ic %o"ld renameexisting le lename to ne%le7

$ mv filename newfile

$ Te mv command %o"ld mo(e existing le

com'letel# into ne% le. o in tis case #o"%o"ld ne onl# ne"#le in #o"r c"rrentdirector#.

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e e ng es To delete an existing le "se te rm

command. Its )asic s#ntax is *

$ rm filename /a"tion7 It ma# )e dangero"s to delete a

le )eca"se it ma# contain "sef"l

information. o )e caref"l %ile "sing tiscommand. It is recommended to "se -io'tion along %it rm command.

Follo%ing is te exam'le %ic %o"ldcom'letel# remo(e existing le lename7$ rm filename

$ 18

t U t


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tan ar Un x treams Under normal circ"mstances e(er# Unix

'rogram as tree streams lesC o'ened for it

%en it starts "' * stdin $ Tis is referred to as standard in'"t and

associated le descri'tor is ?. Tis is alsore'resented as T+IN. Unix 'rogram %o"ld read

defa"lt in'"t from T+IN. stdout $ Tis is referred to as standard o"t'"t and

associated le descri'tor is 1. Tis is alsore'resented as T+,UT. Unix 'rogram %o"ld %rite

defa"lt o"t'"t at T+,UT stderr $ Tis is referred to as standard error and

associated le descri'tor is 2. Tis is alsore'resented as T+00. Unix 'rogram %o"ld %rite all

te error message at T+00 1:

%dentify the three #les the &nix system automatically opens to

execute pro'rams and describe their function

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Management A director# is a le %ose sole @o) is to

store le names and related information.All les& %eter ordinar#& s'ecial& ordirector#& are contained in directories.

UNIX "ses a ierarcical str"ct"re fororganizing les and directories. Tisstr"ct"re is often referred to as adirector# tree . Te tree as a single root

node& te slas caracter


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4ome +irector# Te director# in %ic #o" nd #o"rself %en #o"

rst login is called #o"r ome director#. Go" %ill )e doing m"c of #o"r %or! in #o"r ome

director# and s")directories tat #o"9ll )e creatingto organize #o"r les.

Go" can go in #o"r ome director# an#time "singte follo%ing command * $cd ~ 4ere ( indicates ome director#. If #o" %ant to go

in an# oter "ser9s ome director# ten "se te

follo%ing command * $cd ~username To go in #o"r last director# #o" can "se follo%ing

command * $cd -

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;atnames

Te pathname of a le incl"des tele name and te name of te

director# tat olds te le& andte name of te director# tatolds te director# tat olds te

le& and te name of te H "' tote root

Te 'atname of e(er# le in a

gi(en flesystem is "ni"e.


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;atnames cont.C

To create a 'atname #o" start atte root so #o" start %it


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;atname xam'les

/

bin/ etc/ home/ tmp/ usr/

Hollid2/ scully/ bin/ local/

netprog unix/ X ls who

/usr/bin/lsSyllabus

/home/hollid2/unix/Syllabus


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A)sol"te ;atnames +irectories are arranged in a ierarc# %it

root


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0elati(e ;atnames

A 'atname can also )e relati(e to #o"r c"rrent

%or!ing director#. 0elati(e 'atnames ne(er)egin %it


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3isting +irectories To list te les in a director# #o" can "se

te follo%ing s#ntax *$ls dirname Follo%ing is te exam'le to list all te

les contained in


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/reating +irectories +irectories are created )# te follo%ing

command *$mkdir dirname

4ere& director# is te a)sol"te or relati(e

'atname of te director# #o" %ant tocreate. For exam'le& te command *$mkdir mydir

$

/reates te director# m#dir in te c"rrentdirector#.

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/reating +irectories


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/reating +irectories 4ere is anoter exam'le *

$mkdir /tmp/test-dir Tis command creates te director# test-dir in

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/reating ;arent +irectories ometimes %en #o" %ant to create a director#& its

'arent director# or directories migt not exist. Intis case& m!dir iss"es an error message as follo%s*$mkdir /tmp/amrood/test

mkdir !ailed to make directory"/tmp/amrood/test"#

o such file or directory

In s"c cases& #o" can s'ecif# te -p o'tion to tem!dir command. It creates all te necessar#

directories for #o". For exam'le *$mkdir -p /tmp/amrood/test

$

A)o(e command creates all te re"ired 'arentdirectories. 2


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0emo(ing +irectories +irectories can )e deleted "sing te rmdir

command as follo%s *$rmdir dirname

Note * To remo(e a director# make sure it isempty %ic means tere so"ld not )e an#

le or s")-director# inside tis director#. Go" can remo(e m"lti'le directories at a time as

follo%s *

$rmdir dirname% dirname& dirname3 A)o(e command remo(es te directories

dirname1& dirname2& and dirname2 if te# areem't#. Te rmdir command 'rod"ces no o"t'"t

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/anging +irectories Go" can "se te cd command to do more tan

cange to a ome director#7 Go" can "se it tocange to an# director# )# s'ecif#ing a (alida)sol"te or relati(e 'at. Te s#ntax is asfollo%s *

)cd dirname 4ere& dirname is te name of te director# tat

#o" %ant to cange to. For exam'le& te

command *)cd *usr*local*bin

/anges to te director#


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0enaming +irectories Te m( mo(eC command can also )e

"sed to rename a director#. Te s#ntax isas follo%s *$mv olddir newdir

$ Go" can rename a director# m#dir to

#o"rdir as follo%s *

$mv mydir yourdir$

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Te directories dotC and dot dotC


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Te directories . dotC and .. dot dotC Te lename . dotC re'resents te c"rrent

%or!ing director#J and te lename .. dot dotC

re'resent te director# one le(el a)o(e tec"rrent %or!ing director#& often referred to aste 'arent director#.

If %e enter te command to so% a listing ofte c"rrent %or!ing directories les and "se te-a o'tion to list all te les and te -l o'tion'ro(ides te long listing& tis is te res"lt.

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Unix - File ;ermission < Access Modes

File o%nersi' is an im'ortant com'onent of

UNIX tat 'ro(ides a sec"re metod for storingles. (er# le in UNIX as te follo%ingattri)"tes *

O"ner permissions * Te o%ner9s'ermissions determine %at actions te o%nerof te le can 'erform on te le.

,roup permissions * Te gro"'9s 'ermissions

determine %at actions a "ser& %o is amem)er of te gro"' tat a le )elongs to& can'erform on te le.

Other "orld. permissions * Teermissions for oters indicate %at action all

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T ; i i I di t


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Te ;ermission Indicators $ile "sing ls -l command it dis'la#s (ario"s

information related to le 'ermission as follo%s*

4ere rst col"mn re'resents dierent accessmode ie. 'ermission associated %it a le or

director#. Te 'ermissions are )ro!en into gro"'s of

trees& and eac 'osition in te gro"' denotesa s'ecic 'ermission& in tis order7 read rC&

%rite %C& exec"te xC * 55

e erm ss on n cators


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e erm ss on n cators

Te rst tree caracters 2-6C re'resent te'ermissions for te le9s o%ner. For exam'le

-r"xr-xr-- re'resents tat on%er as read rC&%rite %C and exec"te xC 'ermission.

Te second gro"' of tree caracters 8-C consistsof te 'ermissions for te gro"' to %ic te le

)elongs. For exam'le -r"xr-xr-- re'resents tatgro"' as read rC and exec"te xC 'ermission )"tno %rite 'ermission.

Te last gro"' of tree caracters E-1?C

re'resents te 'ermissions for e(er#one else. For56

File Access Modes


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File Access Modes Te 'ermissions of a le are te rst line of

defense in te sec"rit# of a Unix s#stem. Te

)asic )"ilding )loc!s of Unix 'ermissions arete read& %rite& and exec"te 'ermissions& %icare descri)ed )elo% *

/+ 0ead Krants te ca'a)ilit# to read ie. (ie% te

contents of te le.

1+ 2rite Krants te ca'a)ilit# to modif#& or remo(e

te content of te le.

3+ 4xecute

User %it exec"te 'ermissions can r"n a le58

+irector# Access Modes


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+irector# Access Modes +irector# access modes are listed and organized in

te same manner as an# oter le. Tere are a fe%

dierences tat need to )e mentioned71. 0ead

Access to a director# means tat te "ser can read tecontents. Te "ser can loo! at te lenames inside te

director#.2. $rite

Access means tat te "ser can add or delete les to tecontents of te director#.

5. xec"te xec"ting a director# doesn9t reall# ma!e a lot of sense so

tin! of tis as a tra(erse 'ermission. A "ser m"st a(e exec"te access to te )in director# in

order to exec"te ls or cd command. 5:

/anging ;ermissions


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/anging ;ermissions

To cange le or director# 'ermissions& #o" "sete chmod cange modeC command. Tere are

t%o %a#s to "se cmod7 s#m)olic mode anda)sol"te mode.

&sin' chmod in Symbolic 5ode Te easiest %a# for a )eginner to modif# le

or director# 'ermissions is to "se tes#m)olic mode. $it s#m)olic 'ermissions#o" can add& delete& or s'ecif# te

'ermission set #o" %ant )# "sing te5

Using cmod in #m)olic Mode


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Using cmod in #m)olic Mode

Chmodoperator

Description

Adds te designated 'ermissionsC to ale or director#.

-0emo(es te designated 'ermissionsC

from a le or director#.

6 ets te designated 'ermissionsC.

5E

Mode


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Mode 4ere9s an exam'le "sing testle. 0"nning ls -%

on testle so%s tat te le9s 'ermissions are as

follo%s *

Ten eac exam'le cmod command from te'receding ta)le is r"n on testle& follo%ed )# ls -lso #o" can see te 'ermission canges *

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/anging ,%ners and Kro"'s


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/anging ,%ners and Kro"'s $ile creating an acco"nt on Unix& it assigns a

o%ner I+ and a gro"' I+ to eac "ser. All te

'ermissions mentioned a)o(e are also assigned)ased on ,%ner and Kro"'s.

T%o commands are a(aila)le to cange te

o%ner and te gro"' of les * cho"n * Te co%n command stands for

cange o%ner and is "sed to cange teo%ner of a le

ch'rp * Te cgr' command stands forcange gro"' and is "sed to cange tegro"' of a le.

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/anging ,%nersi'


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/anging ,%nersi' Te co%n command canges te o%nersi' of

a le. Te )asic s#ntax is as follo%s *

$ chown user filelist Te (al"e of "ser can )e eiter te name of a

"ser on te s#stem or te "ser id "idC of a "ser

on te s#stem. Follo%ing exam'le *

$ chown amrood testfile

/anges te o%ner of te gi(en le to te "seramrood. 7OT4: Te s"'er "ser& root& as te "nrestricted

ca'a)ilit# to cange te o%nersi' of a an# le )"t

normal "sers can cange onl# te o%ner of les te#o%n61

,%nersi'


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,%nersi' Te crg' command canges te gro"'

o%nersi' of a le. Te )asic s#ntax is asfollo%s *

$ ch'rp 'roup filelist Te (al"e of gro"' can )e te name of a gro"'

on te s#stem or te gro"' I+ KI+C of a gro"'on te s#stem.

Follo%ing exam'le *

) ch'rp special test#le

/anges te gro"' of te gi(en le to s'ecialgro"'.

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a 'rocess in Unix terminolog#


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a 'rocess in Unix terminolog# $en #o" exec"te a 'rogram on #o"r UNIX

s#stem& te s#stem creates a s'ecial

en(ironment for tat 'rogram. Tisen(ironment contains e(er#ting needed forte s#stem to r"n te 'rogram as if no oter'rogram %ere r"nning on te s#stem.

$ene(er #o" iss"e a command in UNIX& itcreates& or starts& a ne% 'rocess. $en #o"tried o"t te ls command to list director#

contents& #o" started a 'rocess. 8 process9 insimple terms9 is an instance of a runnin'pro'ram+

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/+; 4xplain a process in &nix terminolo'y and themeanin' of


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a 'rocess in Unixterminolog#

Te o'erating s#stem trac!s 'rocessestro"g a (e digit I+ n"m)er !no%n as

te 'id or 'rocess I+ . ac 'rocess inte s#stem as a "ni"e 'id.

;ids e(ent"all# re'eat )eca"se all te

'ossi)le n"m)ers are "sed "' and tenext 'id rolls or starts o(er. At an# onetime& no t%o 'rocesses %it te same

'id exist in te s#stem )eca"se it is te66


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Inter-'rocesscomm"nication

Inter-'rocess comm"nication I;/C refers to temecanisms


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File descri'tors

ac le a 'rocess as access to isidentied )# a small nonnegati(e

integer& called a le descri'tor. Filedescri'tors are created )# s#stem calls%ic o'en les and are inerited )#

ne% 'rocesses %ic are for!ed ofrom te c"rrent 'rocess. Tat is& %ena 'rocess starts a ne% 'rogram& teoriginal 'rocess9s o'en les arenormall inerited ) te ne% ro ram.

6:

Fil d i t


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File descri'torsB# con(ention& most 'rograms reser(e

te rst tree le descri'tors ?& 1& and2C for a s'ecial '"r'oses -- access tote so-called standard input&

standard output& and standarderror streams. File descri'tor ? is standard in'"t& %ere

man# 'rograms ex'ect to recei(e in'"tfrom te o"tside %orld.

File descri'tor 1 is standard o"t'"t. Most'rograms dis'la# normal o"t'"t tere.

For o"t'"t related to error conditions& le6

Unix le access 'rimiti(es


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Unix le access 'rimiti(es

%ill next disc"ss o% to do I


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'rimiti(es7

o'en - o'en for reading or %riting& or

create an em't# le creat - create an em't# le close - read - get info from le %rite - '"t info in le lsee! - mo(e to s'ecic )#te in le "nlin! - remo(e a le remo(e - remo(e a le

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File I


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File I


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File I


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Oincl"de P "nistd. Q

mainC R

int fdJ ssizeSt nreadJ

car )"f1?26J

fd V o'endata& ,S0+,N3GCJ


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Oincl"de P stdli). Q

Oincl"de P fcntl. Q

car =%or!leV@"n!J

mainC

R

int ledesJ

if ledes V o'en%or!le& ,S0+$0CC VV -1C

R

'rintf/o"ldn9t o'en sYn& %or!leCJ

exit1CJ


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Oincl"de P s#s


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%riteco'# data from 'rogram )"er to external le

GN,;I Oincl"de P "nistd. Q

ssizeSt %riteint ldes& const (oid =)"f& sizeSt n)#teCJ

+/0I;TI,N

Te %riteC f"nction attem'ts to %rite n)#te )#tesfrom te

)"er 'ointed to )# )"f to te le associated %itte

o'en le descri'tor& ldes. +ata T#'e7 ssizeSt

Tis data t#'e is "sed to re'resent te sizes of )loc!s tatcan )e read or %ritten in a single o'eration

8:

xam'le of "se7


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xam'le of "se7int fdJ

ssizeS1t %1& %2J

car )"f1812& )"f21?26l

... ll )"f1 and )"f2

if fdVo'ensomele& ,S$0,N3G Z ,S/0AT Z ,SX/3&?:66CC VV -1C

ret"rn -1Cl

%1 V %ritefd& )"f1& 812CJ

%2 V %ritefd& )"f2& 1?26CJ

%ill %rite 185: )#tes to somele& o(er%riting an#ting

tere alread# 8

t d d I


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tandard I


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/ li) f tiint getcar(oidC


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/ li)rar# f"nction -getcarC

Te / li)rar# f"nction int getcar(oidC gets acaracter an "nsigned carC from stdin. Tis is

e"i(alent to getc %it stdin as its arg"ment. Follo%ing is te declaration for

'etchar() function

Tis f"nction ret"rns te caracter read as an"nsigned car cast to an int or ,F on end of leor error.

:?


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/ li)rar# f"nction - 'rintfC

Te / li)rar#

function int printf(const char *format+ ,,,)

sends formatted o"t'"t to stdo"t.

Follo%ing is te declaration for 'rintfC f"nction.

int printf(const char *format+ ,,,)

format * Tis is te string tat contains te text to )e%ritten to stdo"t.

:1

xam'le


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'Oincl"de Pstdio.Q

int main CR

car cJ

'rintfnter caracter7 CJ

c V getcarCJ

'rintf/aracter entered7 CJ

'"tcarcCJ

ret"rn?CJ

W :2


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xam'le

3et "s com'ile and r"n te a)o(e'rogram tat %ill 'rod"ce te follo%ing

res"lt7nter caracter7 a

/aracter entered7 a

Documents

2. Basic Commands of Unix