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History of Unix 1970-1974, Simple is beautiful

early stage of AT&T Bell Lab, on PDP-11 machine Unix is not an acronym, but a weak pun on MULTICS

1976, first licensed release, Version 6

1978, first portable version, Version 7

1979, Berkeley 3BSD

1983, System V as industry standard

1984, Microsoft releases Xenix

1986, BSD 4.3, AT&T Version 9

1987, SVR4, Mach,

1993, Linux

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Unix Philosophy

Easy to program by combining small building blocks

Not (naive) user friendly

A clean minimal design (nothing extra, nothing unnecessary)

Open access:

Provide tools and mechanism to combining the tools Minimal restrictions to the ways of doing things

A user can be very creative (and frustrated).

Major Unix OS features:

Kernel

Shell

File System

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Unix Operating System Structure

OS mediates between the user and the computer

User

Application Programs

Kernel

Hardware

Shell

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Kernel

Manages memory and allocates it to each process

Schedules work done by the CPU

Organizes transfer of data from one part of machine toanother

Accepts instructions from shell and carries them out Enforces access permission on the file system

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Shell

Command interpreter

Create customized environments

Write shell scripts

Define command aliases

Manipulate command history

File and command completion

Edit the command line

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File System

Logical method for organizing and storing large amounts of

information. Easy to manage.

File: basic storage unit.

Types: ordinary file (stores info)

directory (holds other files and directories)

special file (represents physical devices like printers, terminals, etc)

pipe (temporary file for command linkage)

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UNIX: Multi-user Multi-tasking

More than one user can run at the same time and more than

one task can run at the same time Unix is multiuser multitasking, Window NT is, Windows is not.

In Unix, each program is started as a process.

A process is a program in execution. Usually only one copy of a program, but there may be many

processes running the same program.

To each interactive user (window): only one process in foreground may have several processes in background

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httpd

lpd

Processes

/etc/init

kernel Process 0: Kernel bootstrap. Start process 1.

Process 1: create processes to allow login.

inetd/etc/getty

fork

exec

/bin/login

exec

shell

exec

/etc/getty

fork

exec

/bin/login

exec

shell

exec

condition terminal for login

check password

command interpreter

kernal modeuser mode

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Unix Process Init process

last step in booting procedure create other processes to allow the users to login

Getty process

conditions for terminal connection

wait for user-id display login on the screen

Login process

check password with the uid

execute .profile or .login (depends on default shell)

display shell prompt

Shell process (command line interpreter)

Shell prompt ($, %)

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UNIX Process

Process environment

Process id, parent-process-id, process-group-id

Opened files

Working directory

File creation mask

User ID, Group ID

Resource limits

Environment variables

Code A child process inherits parents environment.

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Processes

useps to see the processes that you are running.

$ ps

PID TTY TIME CMD

221 pts/4 4:15 netscape

201 pts/4 0:05 bash215 pts/4 1:15 emacs-19

use & to execute a task in background Example: $ sort infile > outfile &

use ctrl-Z to suspend the foreground task, and then use bg.

use fgto move a background task to foreground.

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Shell: Command Interpreter

Bourne Shell: the default shell (sh)

original unix shell

does not have interactive features of newer shells

widely used for writing shell scripts

standard on Unix System V

C Shell (csh): available on BSD Unix and most other systems

with syntax similar to the C language

with many enhancement over the Bourne shell.

Korn Shell (ksh): AT&Ts answer to C Shell combine features of Bourne and C shells

very efficient

Other shells: tcsh, bash

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Day-to-Day UseCommand Function Meaningcat Display a file conCATenate

cp Copies a file CoPymv Renames a file or moves it MoVerm Delete files ReMovelpr Sends a file to a printer Line Printerlp (Sys V)ls Lists the contents of a directory LiStchmod Changes the mode of permissions Change MODepwd Shows the current directory Print WorkingDircd Change current directory Change Dirmkdir Create a directory MaKe DIRrmdir Delete a directory ReMove DIR

ps Shows the processes on the system Process Statusman Shows info. about commands Manualdf Shows file system status Disk Filedu Shows the space allocation of files Disk Utilizationgrep Search for patterns in files

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Standard Command Format command [options] [arguments]

wc [-c | -m | -C] [-lw] [file]

stuff in brackets is optional

boldface words are literals (must be typed as is)

italicized (or enclosed) words are args (replace appropriately)

Options modify how the command works

command [options] [--] [ ]

options ::= -option white-space options*

option ::= noargoption* argoption | noargoption+

noargoption ::= letterargoption ::= letter whitespace string

$cc -po zap zap.c

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Some Examples

ls [-alRF] file-list

a for listing all files including the dot files

l for long format (file type, permissions, #links, owner, group, etc)

R for recursive, list subdirectories.

F for listing directories with a trailing /

ps []

List the information about running processes

Example:

%ps -el # print the info about all processes (e) in the long format (l)

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On-line Documentation For shell command, system programs, and library functions.

%man [n] e.g.

%man wait %man 1 wait

%man man %man 1 man

%man -k

Man(ual) page format

Name

SynopsisDescription (options, defaults, detail desc., examples)

Files

See Also

Bugs

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I/O Redirection

Redirection and Pipe

> redirects standard output (screen) to a file

E.g. ls > dirlist

outfile

| pipe output of program 1 to input of program 2

E.g. who | wc

Or getit < in | check_it | process_it | format_id > out

>> appends output to a fileE.g. ls -l >> oldfile

Exercise: find out the definition of tee.

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Sequential vs. Concurrent Process

Sequential:

%date

%ps -ef OR %date; ps -ef; who

%who

Concurrent:%pgm1 & prgm2 > file1 & pgm3%make > log &

%sort +1 pdir; ((pr dir | lpr) & sort +1 local))

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File Name Expansion

Each shell program recognizes a set of special characters

called meta characters. The metacharacters are used to create patterns to match

filenames and command names.

Bourne and Korn shell meta/wildcard characters * matches any string (including null)

? matches any one character

[a-dA-D] matches any one character in the range

[!AB123] matches a char not in this range \ escape

~ : (not bourne shell) the home dir of the user.

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File Name Expansion

Assume we have the following files under the current

directory: 120, 235, 2#5, a.out, c22, c*2, Doc.1, Doc.2,Doc.3, one.c,two.c, three.c

ls *.c ls c*2ls [a-z]*[!0-9] a.* *.*

ls ??? cd ~foo

ls *

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Filters

Most UNIX utilities are filters

A filter is a program which reads input (text) from standard input only

writes output to standard output only

writes error to standard error only may use temporary files for intermediate results

Filters can be combined to work together using pipes

Pipe: takes stdout of one command and uses it as stdin of

another command

ls | wc

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Command Alias

Assign your own name for a command

Syntax is shell dependentalias ll ls -l C shell

alias ll=ls -l Korn, Bourne shell

Displaying the value of an aliasalias ll (displays value)

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Unix File Systems

File: a collection of data

Just a sequence of bytes

no record or block structure required

Directory

A file that contains information for files distinction between a directory and a file

system can alter the contents of a directory

rooted tree file structure (inverted tree)

directories can contain both files and other directories info.

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5binbinetc

Unix File System Road Map

Special files: /dev/* represents I/O devices.

/

/etc /var /bin /tmp /usr /mnt /home

sue john

passwd

hosts... spool admprintermail(in)mail(out)uucp

messageswtmp

libinclude

/dev

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File Systems and the I-nodes

Each disk drive contains one or more file systems

Each file system occupies a number of cylinder groups.

Each file system has a superblock, an i-node table and files

The superblock is at a fixed location relative to the beginning

of the file system. It contains a description of the file system. One can find the location of the I-node table thru superblock.

Each entry of the I-node table is an I-node, which uniquelyrepresents a file in the file system.

An I-node contains uid, gid, time of creation, modification,

and access, permissions, location of the file on the disk.

superblock I-node table file1 file2 free file3 free

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Inodes od -b .

0000000 4 ; . \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \00000020 277 ( . . \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \00000040 390 = b l a h \0 \0 \0 \0 \0 \0 \0 \0 \0 \0

0000060

A filename is a link(links name in directory hierarchy to theinode, thus to the file contents)

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Directories Directory is an ordinary file

can be read as ordinary files (by any program that reads text) cant be created or written as ordinary files (only system can)

od - octal dump

cat foo

hi therewelcome to unix

od -c myfile (output in decimal by byte pairs)

0000000 h i t h e r e \n w e l c o m e0000020 t o u n i x \n0000031

1st 7-digits are position in file, ordinal number of next

character (in octal)

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Symbolic Links

Can have many links to the same file (inode)

rm - does not remove inode, removes directory entry (link)

Only when all links are gone is the file (inode) removed

ln -command for creating symbolic links ln oldfile newfile (creates another link to the inode)

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Permissions

Every file has a set of permissions associated with it

three types of permissions: read ( r), write (w), and execute (x) three sets of permission: user, group, world.

In Unix system, users are identified by numbers:uid, gid

ls -l-rwxr-xr-x 1 root 3743 Jan 4 1970 test

user group others #links owner size (time of last mod) (file name)

Problem: how do you write a program which allows differentusers to access a set of files? E.g. the program passwd

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Permissions (cont.)

Solution: use the set-uid bit

When a user execute a program with the set-uid bit set, theuser assume the identity of the owner of the program.

For examplels -l /bin/passwd

-rwsr-xr-x 1 root 8454 Jan 4 1994 /bin/passwd

set-uid

Set-uid bit may break the security wall. (users can run the/bin/passwd and act like root)

Only special programs can be set-uid program, particularly ifthe owner is root.

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Chmod

Change the access permissions of a file

chmod permissions can be specified as 3 octal digits, ,

the three bits of an octal means r,w,x Example: chmod 755 test

permissions can be specified as +x, or u+x, or g+r,

chmod +s test sets the set-uid bit for file test.

If a directory has x in its permision, the dir is searchable, ie.,

one can do ls on the directory.

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Pathnames

Every file and directory in the file system can be identified by

a full path name (route from root to file)/home/sue/email/f1

Relative path name

location relative to current directory. Current directory.. Parent directory

if cwd is /home/sue:ls email

ls ./email

cd ..

ls ../fred

fred

/

home

sue

docs email

f1 f2

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Mounting File Systems

A file system must be mounted before it can be used

Root file system is mounted at boot time.

A file system can be mounted to a dir. of another mounted fs.

Mounting is done in memory

/

/etc /var /bin /tmp /usr /mnt /home/dev

a file system

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Whats Next?

Shell scripts!

But first, some details

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Some Details

cp [-ir] file1 file2

cp [-ir] file-list directory i for interactive. prompt use whenever a file will be overwritten

r for recursive. copy a directory tree

ls [-alRF] file-list a for listing all files including the dot files

l for long format

R for recrusive. list the all subdirectories.

F for listing directories with a trailing /

date [+format]

%date +%h %d, 19%y

Oct 1, 1996

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Some Details (cont.) wc file-list

display the number of lines, words and charaters

more file-list

Browse through text files on page at a time.

head [-n ] file-list

Display the first n lines of the files (default=10)

tail [+n|-n| -f| ]

Display the last few lines in the files (default = 10)

Example:%tail +5 foo # display the last parf of foo starting from line 5

%tail -5 foo # display the last five lines of foo

%tail +30 foo | head -15 | more #display line 30-45 of foo

%tail -f foo # wait and display the new lines appended to foo

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Some Details (cont.) cut -c list file

cut -f list [-dChar] file Cut out selected charaters or fields from each line of a file

Examples:

%cut -c 1-5,15-20 foo

# extract chars 1-5 and 5-20 from each line of foo.%cut -f 1,3 -d moo # extract field 1 and 3 from each line of moo.

paste file1 file2

Concatenate corresponding lines of the given input files Example (reverse two fields of the file abc)

%cut -f1 abc > abc1

%cut -f2 abc > abc2

%paste abc2 abc1 > xyz

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Some Details (cont.)

grep, egrep, fgrep

grep [-nv...] pattern [file-list] Search the input text files for lines matcing the pattern

%grep Unix doc.1 # Display the lines in doc.1 that contains Unix

%grep -n Unix doc.* # Display the lines with line numbers%grep -v Unix doc.1 # Display the lines which do not contain Unix

sort [-tC] [-o outfile] [field-list] [file-list]

sort the files

%sort +1 list1 # sort list 1 starting from field 2 to the end of the line%sort +2-3 list2 # sort list2 on the third field

%sort -n -o list4 list3 sort list3 numerically and place the output in list4

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diff

diff file1 file 2

Display different lines that are found when comparing two files It prints a message that users ed-lide notation (a - append, c -

change, d -delete) to describe how a group of lines has changed.

It also describes what changes need to be made to the first file to

make it the same as the second file. Example

file1 file2 file3

apples apples oranges

oranges oranges bananas

bananas kumquats kiwis

peaches

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diff (cont.)

%diff file1 file2

3c3kumquats

%diff file1 file3

1d0

kiwis

>peaches

fil 1 fil 2

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comm file1 file2 Takes two sorted text fiels and print common lines and lines which

appear exclusively in one file on separate colmns.

column1: lines only in file1, column 2: lines only in file2; col 3:comm

Example

file1 file2 %comm file1 file2

apple apple applebanana cantaloup banana

grape grade cantaloup

orange kiwi grape

lemon kiwi

%comm -12 file1 file2

apple

grape

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tr [-csd] pattern1 pattern2

Translate input character to output character based on the input

and output patterns Example

%tr [A-Z] [a-z] out

# xlate all letters to lower case.

%tr -s \012\011\040 \012\012\012 < in > out# xlate blank, tab and newline chars to newline chars and

squeeze (-s) consecutive newline char into one

%tr -cs [a-z][A-Z] [\012*] < in > out

# change all non-aplphbetic (-c) chars to newline chars andsqueeze consecutive newlne char into one.

%tr -d \040 < in > out

# delete all blanks.

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uniq [-cdu] file-list

Display a fiel, removing all successive repeated lines

Example:file1: %uniq file1

apple apple

banana banana

banana apple

apple

banana

%sort fruit | uniq -capple 2

banana 3

%tr -cs [a-z][A-Z] [\012*] < fileA | sort | uniq

# show a list of distinct words in fileA.

f

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find

Recursively search the directory tree rooted at and

find all files whose names satisfy There are many details in the expression.

Examples:

%find . -name \*.doc -print # list all files names ending with .doc

%find /etc/source -atime 2 -print# print the names of the files under /etc/source whose lst accesstime was 2 days ago.

%find . -name [a-z]* -exec rm {} \;

# remove the files under the curent directory whose names beginwith a lower case letter.

%find / \(-name a.out -o -name *.o \) -atime +7 -exec {} \;

# remove the object and binary executable files under the rootdireory which have not be accessed more than 7 days.

i i[ d ] [ B ]

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cpio -i[cdv] -o[cBv]

System V file archive and backup progam

Example%find proj -print | cpio -ocBv > /dev/rmt8

# cpio get file names from stdin. -o create archive which isredirected to the tape device.

%find proj -print | cpio -ocBv > proj.cpi

# get file name from stdin and -o createsarchive which isredirected to proj.cpio

%cpio -icdv *.c

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tar [options] [file-list] key := c (create) | t (table of content) |r (append the file) | u (update

the file)

options := v (verbose) | b (block) | f (file name follows) | m (useextraction time as the mod file)

Create/extracting archive files for backup and transporting files

%tar cvf proj.tar proj # create archive file proj.tar from file or dir proj

%tar xvf proj.tar # extract files in proj.tar

% tar tf proj.tar # list of the filenames in proj.tar without extractingdata.

%tar cf - proj | (cd /newproj/; tar xvpf -) # copy proj to the directory/newproj/. p to keep all the protection mode.

cp -r copies a dir tree but all the time info is gone. Tar preserve thetime info.

%tar cbf 20 proj.tar /usr/local/proj # avoid using full path names.When ou extract the file, tar will insist to ut fiels to /usr/local/ ro .

d & d d

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uuencode & uudecode

Generate an ASCII encoded version of the give files

Example:%uuencode file.bin newfile.bin > file.bin.uu

# encode file.bin and put the result in file.bin.uu

%uudecode file.bin.uu

# decode the file file.bin.uu and generate a new file newfile.bin

Sending a dir tree via email

%tar cvf proj.tar proj

%compress proj.tar # compress proj.tar to proj.tar.Z%uuencode proj.tar.Z proj.tar.Z | mail qli

at the receiving end, extract the mail and save it in xx

%uudecode xx

%zcat proj.tar.Z | %tar xvf -

d [ ] | [ ] d d fil li t

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sed [-n] | [-e] sed_cmd file_lists

A stream editor. It copies the lines from the file_list or stdin to

stdout, editing the lines in the process. Examples:

%sed -n /hello/p < input > output

# copy the lines contains hello. -n suppress stdout so only the

lines that matches are copied.

%sed 5,7d file1 # delete lines 5 to 7 from file1. File1 is unchanged.

%sed s/Unix/UNIX/ doc2

#replace the first occurrence of Unix in each line by UNIX.

%sed s/Unix/UNIX/g doc2

# replace all Unix by UNIX

k [ f fil ] [ F ] [ ] [fil ]

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awk [-f progfile] [-Fc] [prog] [files]

Pattern matching and stream editor.

Example: Program awkexample:

BEGIN { linetype=0} # initialization

NR == 1 { print $1 $NF} # if it is the first line, print the last field

/^$/ { print This is an empty line }

/^Unix/ { printf(Line starts with Unix\n %s\n, $0); linetype=1; next;}

/NonUnix$/ { printf(End with NonUnix\n); linetype=0; next;}

linetype == 1 { print $0}END {printf(%d lines processed\n, NR);} # finishing it up

k ( t )

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awk (cont.)

Test data file (awktest):

Line1-field1 this is the las-fieldThis line should not show

Unix is simple and difficult

Hello world is very simple

Next blank line should show

I line some other NonUnix

This line should not show

Bye

k ( t )

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awk (cont.)

%awk -F -f awkexample awktest

Line1-field1 las-fieldThis is an empty line

Line starts with Unix Unix is simple and difficult

Hello world is very simple

Next blank line should show

This is an empty line

End with NonUnix

This is an empty line

11 lines processed

Command line program: most of the awk commands can be used inhe command line.

%awk {print $2 $1} # exchange field1 and field2

Oth C d

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Other Commands chown [-R]

Only owner and root can chown. (Root only in somesystems.Why?)

Example:

%chown -R john testdir

# john becomes the owner of all files under testdir. kill [-signal] pid

Sending the specified singal to the process. The process can beprogrammed to catch most of the signals.

Examples:%kill -1 1 # poke the init process to reinitialize (reading /etc/ttytab)

%kill -9 1234 # kill process 1234

Signals can be spefified by name, e.g., HUP is 1, KILL is 9.

%kill -l # lists signal names

Oth C d ( t )

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Other Commands (cont.)

du [-as.] [dir list] [file list]

Reports the allocated dispace for each file and/or directoryspecified

-a lists all files, -s lists the grand total of each dir given

Examples:

%du -s # print the total disk space used by the files in and under thecurrent dir.

%du -s * # print the disk space used by each file and dir in the currentdir.

k

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make

A tool for maintaining programming projects

make [-isrntqpd] [-f file] [macro-definition] [targets] It allows the users to specify dependencies among different source

and binary files in his/her applications.

-i ignore error code returned by a command

-s silent mode

-r suppress built-in rules

-n no execute mode

-t touch target file -q question before change

-p printout macro definitions and target descriptions

-d debug mode

-f alernative make file name

make (cont )

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make (cont.)

Makefile:

prog: x.o y.o z.occ -o prog x.o y.o z.o -lm

x.o: x.c def.h

cc -c x.c

y.o:y.c def.h

cc -c y.c

z.o:z.c

cc -c z.c

make does depth-first search on the dependency graph

prog

z.c

y.c

def.h

x.c

x.o

y.o

z.o

Makefile format

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Makefile format

a makefile containing explicit dependency lines in the

following format:target1 [target2 ]: [dependency ] [; commands] [#commnets]

[ commands] [#comments]

each command line start with a tab character, and no other lines

should start with a tab.

commands are bourne shell commands

a set of built-in rules are used by make, e.g.:

.c.o: $(CC) $(CFLAGS) -c $ file direct stdout to file

>> prog>>file append stdout to file< prog

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Shell Metacharacters`` run commands the output of produces

() run commands in in a sub-shell$1, $2 arguments to shell file

$var value of shell variable var

\ \c take c literally (dont evaluate)

take literally

take literally, after $, ``, \ interpreted

# comment

var=val assign variable var

p1 && p2 run p1, if successful, run p2

p1 || p2 run p1, if unsuccessful, run p2

Whats going on?

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What s going on?

What processes, programs, pipes, and files are used?

%cat doc1 > out1; wc -l OUT2 ; cat OUT &

%cat doc1 | wc -l

Whats going on?

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What s going on?

% date ; who | wc

Wed Sep 24 16:00:00 PDT 19974 24 182

| higher precedence than ;

% (date ; who ) |wc

5 30 211

Whats Next?

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What s Next?

Shell scripts!

Guidelines for writing Unix

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gCommands/Tools/Scripts

Standard command format

Recognize meta-characters (handle multiple files)

Standard I/O (stdin,stdout, stderr. If file arg is absent use std)

Keep messages and prompts to a minimum.

Provide verbose options Input/output data should be text whenever possible.

Use dot files and environment variables for frequently used

info. Use standard library and tools to save coding effort.

Shell Script

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Shell Script

Bourne Shell/Korn Shell

Topics: pass arguments

global and local variables

macro

functions

Invoking a shell script

$shell_script_file or $sh -options shell_script_file

the script file must have execute-permission.

Environment Variables

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Environment Variables

.profile

PATH=.:$HOME/bin:/bin:/usr/bin:/usr/local

TERM=vt100

export TERM PATH

- HOME -- home directory

PATH -- where to look for commands

TERM -- terminal type for programs such as the editor

CDPATH -- shortcut directories for cd command

PS1 PS2 -- prompt

A shell script example

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A shell script example

The script file loginfo (must be executable):

echo The current date and time: \cdate

echo The number of users: \c

who | wc -l # count number of lines

echo personal info: \c);who am i

exit 0

$chmod +x loginfo

$loginfo

The current date and time: Thursday October 10

The number of users: 7

Personal info: lseiter ttya .

Another Example

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Another Example

$cat shellvariables

#! /bin/sh# show predefined shell variables

echo The number of arguments is $#

date &

echo The process id of date command is $!wait

echo The process id of this shell is $$

grep root /etc/passwd

echo The return code from grep is $?

echo The current set of options is $-

$shellvariables one 2 xyz

$sh -a shellvariables one 2 xyz

Positional parameters

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Positional parameters

set to shell script arguments. e.g.

$my_script a b xy 1 2 3 positional parameters have the values

$0 -- my_script

$1 -- a

$2 -- b$3 -- xy

$4 -- 1 2 3

shift command:

$shift [n]

# parambers $n+1 $n+2 become $1 $2 .

# default value of n is 1

Using Shell Variables

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Using Shell Variables

Symbolic Variables

parameter = valueExamples:

I=5; Y=$I

# There should be no space around the = sign

# More than one command can be in a line separated by ;x = hello there\n; y=Hello

echo $x

dir1=/usr/bob/doc

ls -a $dir1

echo x = $x

Quoting

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Quoting

string take string literally

$echo * $HOME* $HOME

string take string literally, except $,`,\,,

\c take c literally

Quoting & Compound Command

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Quoting & Compound Command

The Quotes from Hell

This is a string\nThe amount is $100.0

quotes all char except \ $ `

quotes all char except

command substitution (grave accent):$echo Users currently on the system:\n `who`

$echo The banner command,\n `banner the banner`

Compound commands: a pipeline, a list, a group (), a command that begins with a certainreserved words: for, if, case, time,

I/O redirection applies to the complete command except a pipeline,

a list and the time command.

test Command or [ ]

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test Command or [ ]

if test $# -eq 0 if [ $# -eq 0 ]

then thenecho no positional param! echo no positional param!

fi fi

options:-r | -w | -x | -f | -d file

# the file is readable, writeable, executable, a file, or a directory.

n1 -eq | -ne | -gt | -ge | -lt | -le n2

# n1 = | | > | >= | < |

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Test Command

Options

File testing Numerical comparison String Comparison-r file n1 -eq n2 str1 = str2-w file n1 -ne n2 str1 != str2-x file n1 -gt n2 str-f file n1 -ge n2

-d file n1 -lt n2n1 -le n

Logical Connectives

!-a-o

Parameter substitution

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Parameter substitution

Parameter substitution

${param}${param:-word}

value of param if defined, otherwise word,param remains undefined

${param:=word}value of param if defined, otherwise word,if param undefined, param defined to word

${param:?word}

if defined, param, otherwise print word and exit shell${param:+word}

word if param defined, otherwise nothing

Commands and Functions

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Commands and Functions

Reserved word commands

[[ test_expression]] if, case, for, select, while, until

command grouping:

(command_list)

{command_list}

Function definition

function id

{compound_list

}

CX command

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CX command

Suppose you want a command cx that will take a filename and

set its execute permission. For example,$cx foo

Need to be able to get the filename from the command line

Shell variables: $1 (first argument), $2 (second), $* (all args)

chmod +x $1

Flow Control

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Flow Control

General Format:

if command_list1 check exit code of the commandthen 0 -> normal termination -> True

command_list2 non-0 -> abnormal termination -> False

elif command_list3

then if test -d /usr; then echo its a dir; fi

command_list4

. $if test -d /dir

else >then

command_listn > echo its a dir

fi >fi

>$

Looping

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Looping

What does this command do?

$wc -l *

6 file110 file2

3 file319 total

What if you would like things formatted nicely?There are 6 lines in file1There are 10 lines in file2There are 3 lines in file3

Loops

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Loops

General Format:

while command(s) check return code of command,do if 0, execute body and loop again

body

done

while test ! -s file1

do

echo file1 does not exist or is still empty

sleep 500

done

Loops

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p

General Format:

until commanddo

body

done

until who | grep $1

do

echo $1 has not logged in yet

sleep 500

done

Shell scripts

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p

for var in listofwords

docommands

done

for f in $*do

x=`wc -l $f`

echo There are `echo $x |cut -f1 -d ` lines in $fdone

Examples

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p

if test ! -f $1

thenecho First arg is not a file

if

if [$NAME = John Doe -a $BAL -gt 5000]then

echo ok

elseecho not okfi

Examples

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if test -f $1

thenecho First arg is a file

elif test -d $1then

echo First arg is a directoryfi