7/25/2019 Operating Systems - CS604 Power Point Slides Lecture 10

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Operating

SystemsLecture 10

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Agenda for Today

Review of previous lecture Input, output, and error redirection in

UNIX/LinuxFIFOs in UNIX/Linux

Use of FIFOs in a program and at the

command line

Recap of lecture

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Review of Lecture 9

UNIX/Linux I! tools and associated

s"stem calls

UNIX/Linux standard files and#ernel$s mechanism for file access

Use of pipe in a program and at the

command line

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Input, Output, Error

Redirection

%ou can use the Linux redirectionfeatures to detach the default files

from stdin, stdout, and stderr andattach other files with them&

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Input Redirection

Input Redirection:

command < input-file

command 0< input-filePurpose:'etach #e"(oard from stdin

and attach )input*file$ to it,

i&e&, )command$ reads inputfrom )input*file$ and not

#e"(oard

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Input Redirection

$ cat < Phones

[ contents of Phones ]$ grep Nauman < Phones

[ output of grep ]

$

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Output Redirection

Output Redirection:

command > output-file

command 1> output-file

Purpose:'etach the displa" screen

from stdout and attach

)output*file$ to it, i&e&,

)command$ sends output to

)output*file$ and not the

displa" screen

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$ cat > Phones

[ your input ]

$ grep Ali Phones > Aliphones

[ output of grep ]

$ find ! -name foo -print > foolog

[ error messages ]

$

Output Redirection

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Error Redirection

Error Redirection:

command "> error-file

Purpose:'etach the displa" screenfrom stderr and attach )error*

file$ to it, i&e&, error messages

are sent to )error*file$ and notthe displa" screen

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$ find ! -name foo -print "> errors

[ output of the find command ]

$ ls -l foo "> errorlog[ output of the find command ]

$ cat errorlog

ls: foo: No such file or directory

$ find # -name ls -print "> #de$#null/bin/ls

$

Error Redirection

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UNI!Linu" #I#Os

I! for communication (etweenrelated or unrelated processes on a

computer

+

UNIX/Linux -"stem

FIFO

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UNI!Linu" #I#Os

. file t"pe in UNIX

!reated with mknod()or

mkfifo()s"stem call or ("

mkfifocommand

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UNI!Linu" #I#Os

Unli#e a pipe, a FIFO must (e

opened (efore using it for

communication

. write to a FIFO that no process

has opened for reading results in a-II0 signal

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UNI!Linu" #I#Os

1hen the last process to write to a

FIFO closes it, an 0OF is sent to

the reader

2ultiple processes can write to a

FIFO atomic writes to preventinterleaving of multiple writes

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UNI!Linu" #I#Os

3wo common uses of FIFOs In client-server applications, FIFOs

are used to pass data between a

server process and clientprocesses

Used by shell commands to passdata from one shell pipeline to

another, without creating temporary

files

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$%ient&Server

$ommunication wit'

#I#Os

client-1 client*4

server

well-known

FIFO

clientFIFO

. . .

readrequest

send reply

readresponsereadresponse

send reply

send

request

send

request

clientFIFO

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$reating #I#Os

mknods"stem call

esigned to create special

!device" files

mkfifo!ommand

mkfifo! li(rar" call

Invo#es mknodsystem call

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$ommand Line Use of

#I#Os

prog1

prog2

prog3

infile

$m%fifo fifo1

$prog& < fifo1 '

$prog1 < infile ( tee fifo1 ( prog"[ Output ]

$

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$ommand Line Use of

#I#Os$man ls > lsdat

$cat < fifo1 ( grep ls ( )c -l '

[] !"#$sort < lsdat ( tee fifo1 ( )c -l

%!#

$

wc *l

infile

fifo+

wc *lipe

sort tee

grep ipe

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Review of previous lectureInput, output, and error redirection

in UNIX/LinuxFIFOs in UNIX/Linux

Use of FIFOs at the command lineRecap of lecture

Recap of Lecture