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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
M t
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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 *
$mkdir /tmp/test-dir Tis command creates te director# test-dir in
te
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/reating ;arent +irectories ometimes %en #o" %ant to create a director#& its
'arent director# or directories migt not exist. Intis case& m!dir iss"es an error message as follo%s*$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 *
$rmdir dirname% dirname& dirname3 A)o(e command remo(es te directories
dirname1& dirname2& and dirname2 if te# areem't#. Te rmdir command 'rod"ces no o"t'"t
if it is s"ccessf"l. 2E
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/anging +irectories Go" can "se te cd command to do more tan
cange to a ome director#7 Go" can "se it tocange to an# director# )# s'ecif#ing a (alida)sol"te or relati(e 'at. Te s#ntax is asfollo%s *
)cd dirname 4ere& dirname is te name of te director# tat
#o" %ant to cange to. For exam'le& te
command *)cd *usr*local*bin
/anges to te director#
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0enaming +irectories Te m( mo(eC command can also )e
"sed to rename a director#. Te s#ntax isas follo%s *$mv olddir newdir
$ Go" can rename a director# m#dir to
#o"rdir as follo%s *
$mv mydir yourdir$
5?
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 *
5
/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.
6?
/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+
65
/+; 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
6
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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.
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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
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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