1. course staff b.s.mahanand.b.e.,(m.tech)., dept of computer science and engg s.j.c.e. mysore....

Course StaffB.S.Mahanand .B.E.,(M.Tech).,Dept of Computer Science and EnggS.J.C.E.Mysore.

B.S.Mahanand .B.E.,(M.Tech).,Dept of Computer Science and EnggS.J.C.E.Mysore.

Introduction to Unix 2

Course Texts

Reference: Learning Unix - for those who have not used Unix before.


Text Book: Unix Concepts &Applications

By Sumitabha Das

Operating SystemsAn Operating System controls (manages)

hardware and software.provides support for peripherals such as

keyboard, mouse, screen, disk drives, …software applications use the OS to

communicate with peripherals.The OS typically manages (starts, stops,

pauses, etc) applications.


Single vs. MultitaskingSome old operating systems could only do

one thing at a time (DOS).Most modern systems can support multiple

applications (tasks) and some can support multiple users (at the same time).

Supporting multiple tasks/users means the OS must manage memory, CPU time, network interfaces, ...


User InterfacesThe User Interface is the software that

supports interactions with a human.Some operating systems directly provide a

user interface and some don't.Windows is an example of an Operating

System that includes a user interface.Unix (the OS) does not directly provide a user

interface.


What is UNIX?UNIX is a popular operating system (OS) in

both engineering and business worldOS is a “super program” that controls sharing

of resources and communication between machines

E.g., Windows, OS/2, VMS, MacOS, UNIXUNIX is available for all platforms


Unix and UsersMost flavors of Unix (there are many) provide

the same set of applications to support humans (commands and shells).

Although these user interface programs are not part of the OS directly, they are standardized enough that learning your way around one flavor of Unix is enough.


Flavors of UnixThere are many versions of Unix that are

used by lots of people:SysV (from AT&T)BSD (from Berkeley)Solaris (Sun)IRIX (SGI)AIX (IBM)LINUX (free software)


Unix History and MotivationThe first version of Unix came from AT&T in

the early 1970s (Unix is old!).Unix was developed by programmers and for

programmers.Unix is designed so that users can extend the

functionality - to build new tools easily and efficiently (this is important for programmers).


Unix History and MotivationK Thomson and D Ritchie at Bell Labs

Wrote first version in assembly then the next version in C; the first “understandable” OS!

UC Berkeley graduate students Enhanced with memory management and

networking capabilities (BDS UNIX)UNIX Today: contain both features

Commercial UNIXLinux


Some Basic ConceptsUnix provides a simple interface to

peripherals (it's pretty easy to add support for a new peripheral).

Unix includes a basic set of commands that allow the user to view/change the system resources (filesystem, processes, peripherals, etc.).


What we will look atIn this course we will learn about:

Unix user accountsthe core set of Unix commandsthe Unix filesystemA couple of special programs called "shells".A number of commonly used applications:

Window system, text editors, programming tools.


The power of Unix is that you can extend the basic commandsWe will also look at how to extend the basic

functionality of Unix:customize the shell and user interface. string together a series of Unix commands to

create new functionality.create custom commands that do exactly what

we want.


UNIX ServicesUNIX facts about programs and files

A file is a collection of data stored on diskA program is a collection of bytes representing code

and data that is stored in a fileWhen a program is started, it is loaded from disk

into RAM. A “running” program is called a processProcesses and files have an owner and a group, and

they protected from unauthorized accessUNIX supports a hierarchical directory structureFiles have a location within the directory hierarchy


UNIX ServicesSharing resources

UNIX shares CPUs among processes by dividing CPU time into slices (typically 0.1 second) and allocating time slices based on their priorities

UNIX shares memory among processes by dividing RAM into equal-sized pages (e.g., 4K bytes) and allocating them; only those pages of a process that are needed in RAM are loaded from disk while pages of RAM that are not accessed are saved back to disk

UNIX shares disk space among users by dividing disks into equal-sized blocks and allocating them


UNIX ServicesUNIX provides communication mechanism

between processes and peripherals Pipe is one-way medium-speed data channel that

allows two processes on the same machine to talk Socket is two-way high-speed data chanel that

allows two processes on different machines to talk

UNIX allows server-client model of communication e.g., X Window systems


UNIX for Users

Basic commandsman, ls, cat, more, page, head, tail, lessmv,cp,rm,lnpwd,cd,mkdir,rmdir,filechmod, groups, chgrp

Editing utilities and terminal typevi, emacs


Getting Started in UNIXObtain an account and logging-in

passwd: utility for changing passwordShells

A middleman program between you and UNIX OS that executes your commands Shell commands vs. utilities vs. system calls

Three popular shells: Bourne, Korn, CShell has a programming language that are

tailored to manipulate processes and files; such program is called shell script


Utilities for Manipulating File mv, cp, rm, ln

move,copy,remove,make links to filesmv [-fi] soutce targetFile .. rename source filenamemv [-fi] soutceList targetDirectory .. move source files into target directorycp [-fip] soutceFile targetFile .. make copy of sourceFile named targetFilecp [-fip] soutceFileList targetDirectory .. copy source files into target directorycp -rR [-fip] soutceDirList targetDirectory .. copy source files into target directory, and copy the directory structure.rm [-fi] fileListrm -rR [-fi] directoryListln [-fns] source [target]ln [-fns] sourceList targetDirectory .. make links to sour files into target directory

file - determine file type $ file hello.c hello.c: c program text


Utilities for Hanling Directorypwd, cd, mkdir, rmdir

print working directorychange directory

cd, pushd, popd

make directoryremove directory


Vi - Editorvi is a visual text editor. Most of you are too young to understand

what a non-visual editor might be!check out the ed editor!

vi shows you part of your file and allows you to enter commands that change something (add new stuff, delete a char or line, etc).


vi modesvi has a couple of modes:

command mode: move the cursor around, move to a different part of the file, issue editing commands, switch to insert mode.

insert mode: whatever you type is put in the file (not interpreted as commands).

when you first start vi you will be in command mode.


Cursor Movement Commands(only in command mode!)

h move left one position

l move right one position

j move up one line

k move down one line

Your arrow keys might work (depends on the version of vi and your terminal)


spacebar also does this

More Cursor Movementw move forward one word

b move backward one word

e move to the end of the word

) move to beginning of next sentence

( move to beginning of current sentence


Scrolling CommandsCTRL-F scroll forward one screen

CTRL-B scroll backward one screen

CTRL-D scroll forward 1/2 screen

CTRL-U scroll backward 1/2 screen


Command that delete stuffx delete character (the one at the cursor)

dw delete word

dd delete line

X delete back one character (backspace)

3x delete 3 characters (any number works)

5dd delete 5 lines (any number works)


Changing Textcw change word (end with Esc)

cc change line (end with Esc)

C change rest of the line

rx replace character with 'x' (could be anything, not just 'x')


Insert ModeIn insert mode whatever you type goes in to

the file. There are many ways to get in to insert mode:

i insert before current position

a append (insert starting after cursor)

A append at end of line

R begin overwriting text


Ending Insert ModeTo get out of insert mode (back to command

mode) you press "Esc" (the escape key).

There is a status line (bottom of screen) that tells you what mode/command you are in.


Saving and ExitingZZ save if changes were made, and quit.

:wq Write file and quit

:w Write file

:w file Write to file named file

:q Quit

:q! Really quit (discard edits)


Searching Commands/text search forward for text

?text search backward for text

n repeat previous search

N repeat search in opposite direction


Other StuffCopying and Yanking (Paste)Remembering positionsSwitching filesRepeating commandsDisplay line numbersRun Unix commands (for example: emacs)


Emacs -Editor

emacs is every bit as cryptic as vi!emacs allows you to customize it with new

commands and keyboard shortcuts.The emacs commands are written in elisp

(a dialect of Lisp), so you need to understand elisp to do serious customization.


Emacs meta keyMany emacs commands are invoked with

sequence of keystrokes.Emacs doesn't have modes like vi – you

can always enter text (at the current cursor position) or commands.

Many commands start with a special keystroke called the metakey. (others use the control key).

The ESC key is (usually) the meta key.


Command List SyntaxThe book shows a list of tons of emacs

commands. The syntax used to show this list looks like this:

C-a C-b (means Ctrl-a , Ctrl-b)M-a M-b (means Esc, a, Esc, b)


Important CommandsExit: C-x C-cSave file : C-x C-sUndo: C-x uGet out of a command: C-g


Cursor movementCursor keys usually work (it depends on how

your terminal is set up and how emacs is configured).

C-f: forward (right arrow)

C-b: backward (left arrow)

C-p: previous line (up arrow)

C-n: next line (down arrow)


Other stuff in emacsMove by words, sentences, paragraphsFile handling – save/load file, etc.Delete char, word, sentence, regionBuffer manipulation (multiple buffers)Searching, replacingAutomatic indentation (major mode)Lots more (try the tutorial, read the book!)


The Environment

The Unix system environment can be set by user

System variables:Unix system is controlled by number of shell variables set by system called system variables which can be seen by executing $set command

Ex- HOME,PATH,IFS,MAIL,PS1,PS2,SHELL,TERM,LOGNAME


.profile : It is the shell script executed during login time.

stty : To set the terminal characteristics

history :It displays previously executed commands.


histsize : Used to store more commands

$_ : Stores the last arguments of the last command

Changing Directory : ~(tilde)~ acts as short hand representation of home

Directory.


UNIX Utilities: man & ls man

on-line help for UNIX commandsman [-s section] wordman -k keyword

Man pages are divided into 8 sections 1. Commands & application programs 2. System calls, 3. Library functions ...

lslist files

ls [options] {fileName}*


UNIX Utilitiesls example

$ ls -alFstotal 151 drwxr-xr-x 2 jaemok mass 512 Mar 2 01:04 ./3 drwxr-xr-x 46 jaemok mass 3072 Mar 2 01:04 ../5 -rwxr-xr-x 1 jaemok mass 5091 Mar 2 01:04 a.out*5 -rwxr-xr-x 1 jaemok mass 5091 Mar 2 01:04 hello*1 -rw-r--r-- 1 jaemok mass 36 Mar 2 01:04 hello.c

5 size in blockdrwxr-xr-x type and file permission1 hard-link countjaemok ownermass group5091 size in bytesMar 2 01:04 modified timea.out filename

Miscellaneous: date, clearIntroduction to Unix 44

Utilities to List File Contentscat,more,page,head,tail,less

cat displays contents of files given on command line (or from standard input) to standard output$ cat > heart blah blah blah ^D$ _

more and page displays contents of files(or input) fitted to rows of terminal, and allows you to scroll.

head and tail only displays given number of lines in the first part or the last part of files(or input).

less is similar to more, but has more functions


File Owner and GroupEvery UNIX process has a owner which is

typically the user name who started it My login shell’s owner is my user name

When a process creates a file, its owner is set to the process’ owner

UNIX represents the user name as user IDEvery UNIX user is a member of a group and

an UNIX process belongs to a group My login shell’s group is my group name (ID)


File PermissionsFile Permissions (ex: rw-r--r--)

owner: rw-, group: r--, others: r--r: read, w: write, x: execute

When a process executes, it has four values related to file permissiona real user ID, an effective user IDa real group ID, an effective group IDWhen you login, your login shell process’

values are your user ID and group ID


File Permission ApplicationWhen a process runs, file permission applies

If process’ effective user ID = file owner Owner permission applies

If process’ effective group ID=file group ID Group permission applies

Otherwise, others permission applies

Super user’s process automatically has all access rights

When creating a file, umask affect permission


Effective User and Group IDA process’ effective user ID

depends on who executes the process, not who owns the executable

E.g., if you run passwd (owned by root), the effective user ID is your ID, not root; then how can it update /etc/passwd file owned by root ?

Two special file permissions set user ID and set group ID When an executable with set user ID permission is

executed, the process’ effective user ID becomes that of executable; the real user ID is unaffected

File permission of /bin/passwd is r-sr-sr-x


Changing File Permissionschmod

change the permission mode of fileschmod [-fR] <absolute-mode> fileListchmod [-fR] <symbolic-mode-list> fileList


chmodabsolute-mode is octal number

if you want a file to have permission setting: rwxr- x--- then, it is an octal number o750 (111 101 000) $ chmod 750 myfile

symbolic-mode-list is comma-separated list of symbolic expressions of form

[who] operator [permissions]who : characters u,g,o,aoperator : -,=.+permissions : r,w,x,s

$ chmod g-rx myfile


Text Handling CommandsThere are many Unix commands that handle

textual data:operate on text filesoperate on an input stream

Functions:SearchingProcessing (manipulations)


Searching Commandsgrep, egrep, fgrep : search files for text

patterns

strings: search binary files for text strings

find: search for files whose name matches a pattern


grep - Get Regular Expressiongrep [options] regexp [files]

regexp is a "regular expression" that describes some pattern.

files can be one or more files (if none, grep reads from standard input).


grep ExamplesThe following command will search the

files a,b and c for the string "foo". grep will print out any lines of text it finds (that contain "foo")

grep foo a b c

Without any files specified, grep will read from standard input:

grep I


Regular ExpressionsThe string "foo" is a simple pattern.grep actually understands more complex

patterns that are described using regular expressions.

We will look at regular expressions used by grep and other programs later.

In case you can't wait - here is a sample:

grep "[A-Z]0{2,3}" somefile


grep options-c print only a count of matched lines.-h don't print filenames-l print filename but not matching line-n print line numbers-v print all lines that don't match!


grep, egrep and fgrepAll three search files (or stdin) for a text

pattern.grep supports regular expressionsegrep supports extended regular expressionsfgrep supports only fixed strings (nothing

fancy)All have similar forms and options.


stringsThe strings command searches any kind of

file (including binary data files and executable programs) for text strings, and prints out each string found.

strings is typically used to search for some text in a binary file.

strings [options] files


The find commandFind searches the filesystem for files whose

name matches a pattern*.Here is a simple example:

find . -name unixtest -print

*Actually find can do lots more!


Text ManipulationThere are lots of commands that can read in

text (from files or standard input) and print out a modified version of the input.

Some possible examples: force all characters to lower caseshow only the first word on each lineshow only the first 10 lines


Common ConceptsThese commands are often used as filters,

they read from standard input and send output to standard output.

Different commands for different specific functionsanother way is to build one huge complex

command that can do anything. This is not the Unix way!


Simple Filtershead tail - show just part of a filecut paste join - deal with columns in a text

file.sort - reorders the lines in a filetr - translate charactersuniq - find repeated or unique lines in a file.


head or tails?head shows just the "head" (beginning) of a

file. tail shows just the "tail" (end) of a file.Both commands assume the file is a text file.


The head commandhead [options] [files]

By default head shows the first 10 lines.Options: -n print the first n lines. Example:

head -20 /etc/passwd


The tail commandtail [options] [files]

By default tail shows the last 10 lines.Options:

-n print the last n lines. -nc print the last n characters+n print starting at line number n+nc print starting at character number n


The tail command (cont.)More Options:

-r show lines in reverse order-f don't quit at end of file.

Examples:tail -100 somefile

tail +100 somefile

tail -r -c somefile


Not all versions

support this option!

The cut commandcut selects (and prints) columns or fields

from lines of text.

cut options [files]

You must specify an option!


cut options-clist cut character positions defined in

list.

list can be:number (specifies a single character position)range (specifies a sequence of positions)comma separated list (specifies multiple positions or ranges)


cut -c examplescut -c1 prints first char. (on each line).cut -c1-10 prints first 10 charcut -c1,10 prints first and 10th char.

cut -c5-10,15,20-

prints 5,6,7,8,9,10,15,20,21,… char on each line.


more cut options-flist cut fields identified in list.

a field is a sequence of text that ends at some separator character (delimiter).

You can specify the separator with the -d option. -dc where c is the delimiter.

The default delimiter is a tab.


Specifying a delimitercut -d: -f1 prints everything before

the first ":" (on each line).

What if we want to use space as the delimiter?

cut -d" " -f1


cut -f examplescut -f1 prints everything before the

first tab.cut -d: -f2,3 prints 2nd and 3rd : delimited

columns.cut -d" " -f2 prints 2nd column using space

as the delimiter.


The paste commandpaste puts lines from one or more files

together in columns and prints the result.

paste [options] files

The combined output has columns separated by tabs.


paste cands votes


GoreBradleyBushMcCainTrumpLetterman


1010101010100

1010101010100

Gore 10Bradley 10Bush 10McCain 10Trump 10Letterman 100

Gore 10Bradley 10Bush 10McCain 10Trump 10Letterman 100

cands votes

paste options-dc separate columns of output with

character c.you can use different c between each column.

-s merge subsequent lines from a single file.



Gore10Bradley10Bush10Letterman100

Gore10Bradley10Bush10Letterman100

Gore 10Bradley 10Bush 10Letterman 100

Gore 10Bradley 10Bush 10Letterman 100

records

paste -s -c"\t\n" records

Gore 10 Bradley10 Bush 10McCain 10 Letterman100

Gore 10 Bradley10 Bush 10McCain 10 Letterman100

paste -s -c"\t\t\n" records

The join commandjoin combines the common lines of 2 sorted

files. Useful for some text database applications,

but not a very general command.Look at examples in the book if you are

interested.


The sort commandsort reorders the lines in a file (or files) and

prints out the result.

sort [options] [files]


sort options-b ignore leading spaces and tabs-d sort in dictionary order (ignore

punctuation)-n sort in numerical order-r reverse the order of the sort

tons more options!


Numeric vs. AlphabeticBy default, sort uses an alphabetical ordering.


381827125687566875

381827125687566875

182738668751256875

182738668751256875

125687518273866875

125687518273866875

sort sort -n

Alphabetic Ordering (uses ASCII)


bbbb BBBBaaaaAAAA0000####$$$$

bbbb BBBBaaaaAAAA0000####$$$$

####$$$$0000AAAABBBBaaaabbbb

####$$$$0000AAAABBBBaaaabbbb

sort

'0' < '9' <'A' < 'Z'< 'a' < 'z' <

ASCII codes

32: 33:! 34:" 35:# 36:$ 37:% 38:& 39:'

40:( 41:) 42:* 43:+ 44:, 45:- 46:. 47:/

48:0 49:1 50:2 51:3 52:4 53:5 54:6 55:7

56:8 57:9 58:: 59:; 60:< 61:= 62:> 63:?

64:@ 65:A 66:B 67:C 68:D 69:E 70:F 71:G

72:H 73:I 74:J 75:K 76:L 77:M 78:N 79:O

80:P 81:Q 82:R 83:S 84:T 85:U 86:V 87:W

88:X 89:Y 90:Z 91:[ 92:\ 93:] 94:^ 95:_

96:` 97:a 98:b 99:c 100:d 101:e 102:f 103:g

104:h 105:i 106:j 107:k 108:l 109:m 110:n 111:o

112:p 113:q 114:r 115:s 116:t 117:u 118:v 119:w

120:x 121:y 122:z 123:{ 124:| 125:} 126:~

32: 33:! 34:" 35:# 36:$ 37:% 38:& 39:'

40:( 41:) 42:* 43:+ 44:, 45:- 46:. 47:/

48:0 49:1 50:2 51:3 52:4 53:5 54:6 55:7

56:8 57:9 58:: 59:; 60:< 61:= 62:> 63:?

64:@ 65:A 66:B 67:C 68:D 69:E 70:F 71:G

72:H 73:I 74:J 75:K 76:L 77:M 78:N 79:O

80:P 81:Q 82:R 83:S 84:T 85:U 86:V 87:W

88:X 89:Y 90:Z 91:[ 92:\ 93:] 94:^ 95:_

96:` 97:a 98:b 99:c 100:d 101:e 102:f 103:g

104:h 105:i 106:j 107:k 108:l 109:m 110:n 111:o

112:p 113:q 114:r 115:s 116:t 117:u 118:v 119:w

120:x 121:y 122:z 123:{ 124:| 125:} 126:~


The tr commandtr is short for translate.tr translates between two sets of

characters.replace all occurrences of the first character

in set 1 with the first character in set 2, the second char in set 1 with the second char in set 2, …

tr [options] [string1 [string2]]


No files! Always standard input!

tr Example




tr A-Z a-z gorebradleybushmccaintrumpletterman

gorebradleybushmccaintrumpletterman

Replace 'A' with 'a', 'B' with 'b', … 'Z' with 'z'

tr can delete-d option means "delete characters that are

found in string1".




tr -d aeiou GrBrdlyBshMcCnLttrmn

GrBrdlyBshMcCnLttrmn

Another tr example - remove newlines



GoreBradleyBushMcCainTrumpLetterman tr -d '\n'

GoreBradleyBushMcCainTrumpLettermanGoreBradleyBushMcCainTrumpLetterman

The uniq Commanduniq removes duplicate adjacent lines from a

file.uniq is typically used on a sorted file (which

forces duplicate lines to be adjacent).uniq can also reduce multiple blank lines to a

single blank line.


uniq examples




uniq GoreBradleyBushMcCainTrumpLetterman


1010101010100

1010101010100

10100

10100

uniq

Shell - a user interfaceA shell is a command interpreter turns text

that you type (at the command line) in to actions:runs a program, perhaps the ls program.allows you to edit a command line.can establish alternative sources of input and

destinations for output for programs.


Running a ProgramYou type in the name of a program and

some command line options:The shell reads this line, finds the program

and runs it, feeding it the options you specified.

The shell establishes 3 I/O channels:Standard InputStandard OutputStandard Error


Programs and Standard I/O


ProgramProgramStandard Input

(STDIN)Standard Output

(STDOUT)

Standard Error(STDERR)

Unix CommandsMost Unix commands (programs):

read something from standard input.

send something to standard output (typically depends on what the input is!).

send error messages to standard error.


Defaults for I/OWhen a shell runs a program for you:

standard input is your keyboard.standard output is your screen/window.standard error is your screen/window.


Terminating Standard InputIf standard input is your keyboard, you can

type stuff in that goes to a program.To end the input you press Ctrl-D (^D) on a

line by itself, this ends the input stream.The shell is a program that reads from

standard input.What happens when you give the shell ^D?


Popular Shellssh Bourne Shell ksh Korn Shell csh C Shellbash Bourne-Again Shell


CustomizationEach shell supports some customization.

User promptWhere to find mailShortcuts

The customization takes place in startup files – files that are read by the shell when it starts up


Startup filessh,ksh:

/etc/profile (system defaults) ~/.profile

bash:

~/.bash_profile

~/.bashrc

~/.bash_logout

csh:

~/.cshrc

~/.login

~/.logout


Wildcards (metacharacters) for filename abbreviationWhen you type in a command line the shell

treats some characters as special.These special characters make it easy to

specify filenames.The shell processes what you give it, using

the special characters to replace your command line with one that includes a bunch of file names.


The special character ** matches anything.If you give the shell * by itself (as a command

line argument) the shell will remove the * and replace it with all the filenames in the current directory.

“a*b” matches all files in the current directory that start with a and end with b.


Understanding *The echo command prints out whatever you

give it:> echo hi

hiTry this:

> echo *


* and lsThings to try:

ls *

ls –al *

ls a*

ls *b


Other metacharacters?Matches any single character

ls Test?.doc

[abc…] matches any of the enclosed characters

ls T[eE][sS][tT].doc[a-z] matches any character in a range

ls [a-zA-Z]*

[!abc…] matches any character except those listed.

ls [!0-9]*


Input RedirectionThe shell can attach things other than your

keyboard to standard input.A file (the contents of the file are fed to a

program as if you typed it).A pipe (the output of another program is fed as

input as if you typed it).


Output RedirectionThe shell can attach things other than your

screen to standard output (or stderr).A file (the output of a program is stored in

file).A pipe (the output of a program is fed as input

to another program).


How to tell the shell to redirect thingsTo tell the shell to store the output of your

program in a file, follow the command line for the program with the “>” character followed by the filename:

ls > lsoutthe command above will create a file named lsout and put the output of the ls command in the file.


Input redirection To tell the shell to get standard input from

a file, use the “<“ character:sort < nums

The command above would sort the lines in the file nums and send the result to stdout.


You can do both!sort < nums > sortednums

tr a-z A-Z < letter > rudeletter


Output and Output AppendThe command ls > foo will create a new

file named foo (deleting any existing file named foo).

If you use >> the output will be appended to foo:

ls /etc >> foo

ls /usr >> foo


PipesA pipe is a holder for a stream of data.A pipe can be used to hold the output of

one program and feed it to the input of another.


prog1prog1 prog2prog2STDOUT STDIN

Asking for a pipeSeparate 2 commands with the “|” character.The shell does all the work!

ls | sort

ls | sort > sortedls


Building commandsYou can string together a series of unix

commands to do something new!Exercises:

List all files in the current directory but only use upper case letters.

List only those files that have permissions set so that anyone can write to the file.


StderrMany commands send error messages to

standard error.This is a different stream than stdout.

The “>” output redirection only applies to Stdout (not to Stderr).

Try this:ls foo blah gork > savedls

(I’m assuming there are no files named foo, blah or gork!).


Capturing stderrTo redirect stderr to a file you need to

know what shell you are using.

When using sh, ksh or bash it’s easy:

ls foo blah gork 2> erroroutput

It’s not so easy with csh...


File DescriptorsUnix progams write to file descriptors, small

integers that are somehow attached to a stream.

STDIN is 0

STDOUT is 1

STDERR is 2

“2>” means redirect stream #2 (sh, ksh and bash)


Csh and Stderr>& merges STDOUT and STDERR and sends to

a file:ls foo blah >& saveboth

>>& merges STDOUT and STDERR and appends to a file:

ls foo blah >>& saveboth


More Csh|& merges STDOUT and STDERR and sends to

a pipe: ls foo blah |& sort

To send STDERR to file “err” and STDOUT to file “out” you can do this:

(ls foo blah > out) >& err


Shell Variables*The shell keeps track of a set of parameter

names and values.Some of these parameters determine the

behavior of the shell.We can access these variables:

set new values for some to customize the shell.

find out the value of some to help accomplish a task.

* From now on I'll focus on sh and ignore csh


Example Shell Variablessh / ksh / bashPWD current working directoryPATH list of places to look for commandsHOME home directory of userMAIL where your email is storedTERM what kind of terminal you haveHISTFILE where your command history

is saved


Displaying Shell VariablesPrefix the name of a shell variable with "$".The echo command will do:

echo $HOME

echo $PATHYou can use these variables on any command

line:

ls -al $HOME


Setting Shell VariablesYou can change the value of a shell variable

with an assignment command (this is a shell builtin command):

HOME=/etc

PATH=/usr/bin:/usr/etc:/sbin

NEWVAR="blah blah blah"


set command (shell builtin)The set command with no parameters will

print out a list of all the shell varibles.

You'll probably get a pretty long list…

Depending on your shell, you might get other stuff as well...


$PS1 and $PS2The PS1 shell variable is your command line

prompt.The PS2 shell variable is used as a prompt

when the shell needs more input (in the middle of processing a command).

By changing PS1 and/or PS2 you can change the prompt.


Fancy bash promptsBash supports some fancy stuff in the prompt

string:

\t is replace by the current time

\w is replaced by the current directory

\h is replaced by the hostname

\u is replaced by the username

\n is replaced by a newline


Example bash prompt======= [foo.cs.rpi.edu] - 22:43:17 =======

/cs/hollingd/introunix echo $PS1

======= [\h] - \t =======\n\w

You can change your prompt by changing PS1:

PS1="Yes Master? "


Making Changes Stick If you want to tell the shell (bash) to always

use the prompt "Yes Master ?", you need to store the change in a shell startup file.

For bash - change the file ~/.bashrc.

Wait a few minutes and we will talk about text editors - you need to use one to do this!


The PATHEach time you give the shell a command line

it does the following:Checks to see if the command is a shell built-

in.If not - tries to find a program whose name (the

filename) is the same as the command.The PATH variable tells the shell where to

look for programs (non built-in commands).


echo $PATH======= [foo.cs.sjce.edu] - 22:43:17 =======/cs/bsm/introunix echo $PATH/home/hollingd/bin:/usr/bin:/bin:/usr/local/bin:/usr/sbin:/usr/bin/X11:/usr/games:/usr/local/packages/netscape

The PATH is a list of ":" delimited directories.

The PATH is a list and a search order.

You can add stuff to your PATH by changing the shell startup file.


Job Control The shell allows you to manage jobs

place jobs in the backgroundmove a job to the foregroundsuspend a jobkill a job


Background jobsIf you follow a command line with "&", the

shell will run the job in the background.you don't need to wait for the job to complete,

you can type in a new command right away.you can have a bunch of jobs running at once.you can do all this with a single terminal

(window).ls -lR > saved_ls &


Listing jobsThe command jobs will list all background

jobs:

> jobs

[1] Running ls -lR > saved_ls &

>The shell assigns a number to each job (this

one is job number 1).


Suspending and Killing the Foreground JobYou can suspend the foreground job by

pressing ^Z (Ctrl-Z). Suspend means the job is stopped, but not

dead.The job will show up in the jobs output.

You can kill the forground job by pressing ^C (Ctrl-C). It's gone...


Moving a job back to the foregroundThe fg command will move a job to the

foreground.You give fg a job number (as reported by

the jobs command) preceeded by a %.

> jobs

[1] Stopped ls -lR > saved_ls &

> fg %1

ls -lR > saved_ls


Quoting - the problemWe've already seen that some characters

mean something special when typed on the command line: * ? []

What if we don't want the shell to treat these as special - we really mean *, not all the files in the current directory:

echo here is a star *


Quoting - the solutionTo turn off special meaning - surround a

string with double quotes:

echo here is a star "*"

echo "here is a star"


Careful!You have to be a little careful. Double

quotes around a string turn the string in to a single command line parameter.

> ls

fee file? foo

> ls "foo fee file?"

ls: foo fee file?: No such file or directory


Quoting ExceptionsSome special characters are not ignored

even if inside double quotes:$ (prefix for variable names)" the quote character itself\ slash is always something special (\n)

you can use \$ to mean $ or \" to mean "

echo "This is a quote \" "


Single quotesYou can use single quotes just like double

quotes.Nothing (except ') is treated special.

> echo 'This is a quote \" 'This is a quote \"

>


Backquotes are different!If you surround a string with backquotes the

string is replaced with the result of running the command in backquotes:

> echo `ls`

foo fee file?

> PS1=`date`

Tue Jan 25 00:32:04 EST 2000


new prompt!

Communication & E-mailNews : It is invoked by user to read any message

that is sent by system adminstator.

Write : Used for two way communications.

Mesg :Makes the user to block the message.

Talk :It is popular communication program which is superior to write.


Communication & E-mailMail : Used when user is not logged in and

message can be viewed,replied,deleted.

Elm and pine : These are mail handlers which are menu driven.

Finger :Gives the details of user with communication features.


Shell ProgrammingShell script – Group of commands has to be

executed & stored in file with extension .sh

Exit – Shell Script termination.

Expr – Used for computation of basic four operation

Set – Assigning values to positional parameters.


Shell ProgrammingConditional Statements- If- If- elif- Case- While- Until- For


introduction and historyPractical Extraction and Report Language

Pathologically Eclectic Rubbish Lister?the Swiss Army chainsaw of scripting

languagescombines the best of C, sh, awk, and sedreleased in 1987 by Larry Wallinitially ported to MPE by Mark Kleinre-ported by Mark Bixby in 1997 with

periodic updates since then


current statuslatest & greatest Perl release v5.6.0 available

for MPE from bixby.orgPerl is not supported by HP, but if your use of

Perl uncovers any underlying MPE or POSIX bugs, then we certainly want to hear from you!

the best way to get assistance with Perl on MPE is to post your questions to HP3000-L


variable namesscalar values

$days # the simple scalar value "days" $days[28] # the 29th element of array

@days$days{'Feb'} # the 'Feb' value from hash

%days$#days # the last index of array @days

entire arrays or array slices (aka lists)@days # ($days[0], $days[1],... $days[n]) @days[3,4,5] # same as @days[3..5]


value constructorsscalar values

$abc = 12345;$abc = 12345.67;$abc = 0xffff; # hex$abc = "a string with a newline\n";

list values@abc = ("cat", "dog", $def);($dev, $ino, undef, undef, $uid, $gid) = stat($file);

hash values$abc{'December'} = 12;

$month = $abc{'December'};


scalar vs. list contextthe context of some operations will

determine the type of the data returnedscalarlist

assignment to a scalar variable will evaluate the righthand side in a scalar context$onerecord = <STDIN>

assignment to a list variable will evaluate the righthand side in a list context@entirefile = <STDIN>


simple statements

terminated with a semicolonmay be followed by one optional modifier

if EXPR unless EXPR while EXPR until EXPR foreach EXPR

$os = 'mpe';$os = 'mpe' if $model == 3000;


compound statementsa block is a sequence of statements

delimited by curly brackets (braces) that defines a scope

compound statements that control flow:if (EXPR) BLOCK if (EXPR) BLOCK else BLOCK if (EXPR) BLOCK elsif (EXPR) BLOCK ... else BLOCK

LABEL while (EXPR) BLOCK LABEL while (EXPR) BLOCK continue BLOCK LABEL for (EXPR; EXPR; EXPR) BLOCK


subroutinessub max { my $max = shift(@_); foreach $foo (@_) { $max = $foo if $max < $foo; } return $max; }

$bestday = max($mon,$tue,$wed,$thu,$fri);

parameters passed via @_ array@_[0] = parm1, @_[1] = parm2, etc@_ is an alias (i.e. call by reference)private variables declared with my

return or the value of the last expression is the functional return value


arithmetic operatorsaddition: +subtraction: -multiplication: *division: /modulus: %exponentiation: **auto-increment and -decrement: ++ --

++$a - increments $a, returns new value$a++ - returns current value, then increments

$a


assignment operatorsworks like C

$a += 2; is equivalent to $a = $a + 2;**= += *= &= <<= &&= -= /=

|= >>= ||= .= %= ^= x=


relational operatorsnumeric comparisons:

< > <= >= == != <=><=> returns -1, 0, or 1 depending on whether

the left argument is numerically less than, equal to, or greater than the right argument

string comparsions:lt gt le ge eq ne cmpcmp returns -1, 0, or 1 depending on whether

the left argument is stringwise less than, equal to, or greater than the right argument


bitwise operatorsshift left: <<shift right: >>AND: &OR: |XOR: ^negation: ~


i/o and file handlesopen files are identified via file handlesuppercase handle names by conventionpredefined file handles: STDIN, STDOUT, STDERR

<FILEHANDLE> in a scalar context reads the next record from the file

<FILEHANDLE> in a list context reads ALL of the remaining records from the file


opening files with open()open(HANDLE, "/file/path") - open for

readingopen(HANDLE, "< /file/path") - open for

readingopen(HANDLE, "> /file/path") - open for

writingopen(HANDLE, ">> /file/path") - open

for appendingopen(HANDLE, "| shell command") - open

pipe for writing


regular expressions

a vast superset beyond standard Unix regexps

a ? modifier to make patterns non-greedy

zero-width lookahead and lookbehind assertions

conditional expressions


using regular expressions$showme=`callci showme`;

if ($showme =~ /RELEASE: ([A-Z]\.(\d)(\d)\.\d\d)/) {

$release = $1; # the matching V.UU.FF $mpe = "$2.$3"; # the matching U and U (i.e. 7.0)

}

$showme =~ s/LDev/Logical Device/gi; # global substitution


predefined variables$| or $OUTPUT_AUTOFLUSH

By default, all Perl output is buffered (0). To enable automatic flushing, set this variable to 1. Needed when doing MPE I/O which is usually unbuffered.

$$ or $PIDPOSIX PID of the current process

$^O or $OSNAMEoperating system name (mpeix)

@ARGV


debugging

invoke the debugger by starting Perl with the -d parameter#!/PERL/PUB/perl -d

examine or modify variablessingle-step executionset breakpointslist source codeset actions to be done before a line is

executed


perl extensionsbinary code residing in an external

NMXL loaded at run timea thin layer of C that allows the Perl

interpreter to call compiled code written in other languages

several extension libraries come bundled with Perl (sockets, POSIX, etc)


System Administrationfdisk – Dividing a disk into partitions

Useradd – Adding users

Usermod and userdel – Modifying and removing users

Umask – To make default file permissions

Fsck – File system checking

Mkfs – Creating file systems


System AdministrationMount - To mount (i.e, attach) a file

system to the root file system.

Init – This daemon maintains the system at one run level.

Lpadmin – Configuring a printer

Lpsat – Obtaining printer and job status


TCP\IP Network AdministrationNetconfig – Confiuring the network

interface.

Ifconfig – Interface Configuration

Ping – Checking the network.

Route – Used to build the kernel routing table to indicate the gateways that have to be used for routing packets destined.


1. course staff b.s.mahanand.b.e.,(m.tech)., dept of computer science and engg s.j.c.e. mysore....

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