UNIX Tools G22.2245-001, Fall 2000

2000 Copyrigths Danielle S. Lahmani

UNIX ToolsG22.2245-001, Fall 2000

Danielle S. Lahmani

email: [email protected]

Lecture 4


Overview

• shell core functionality

• /bin/sh

• /bin/ksh

• /bin/csh


Shell Core Features• Simple and complex commands

• redirection of input/output

• pipes

• wildcards

• command substitution

• background processes

• shell variables

• here documents

• built-in cmds

• programming constructs


The Korn Shell: /bin/ksh• Supports all features described in the Bourne shell

(/bin/sh)

• Alias mechanism

• History mechanism for access of previous commands

• Functions

• Enhanced job control

• Arithmetic

• Tilde substitution


The Korn shell: /bin/ksh STARTUP FILES:

– /etc/profile

– $HOME/.profile

• ALIAS:– alias [-tx] [word[=string]]

– alias -x : to export alias to child shell

– unalias aliasname: to remove an alias


/bin/ksh: History Mechanism• Numbered commands

$ PS1='!!’ /* set prompt to contains a ! */

$HISTSIZE default is 128

• using the built-in vi editor– declare VISUAL=vi or EDITOR=vi– to edit current line, press ESC key to enter the editor

– vi cmds to edit line, when done, press ESC key again,

– additional movement: cursor up (k or - ) cursor down (j or +)

– additional searching /string or ?string : searches backward and forward through history, respectively.


/bin/ksh (continued)

• ARITHMETIC: Using let expression

• TILDE SUBSTITUTION– ~ $HOME

– ~user home directory of user

– ~/pathname $HOME/pathname

– ~+ $PWD

– ~- $OLDPWD


/bin/ksh: FUNCTIONS• Allows functions that may be invoked as shell

commands

function name {

list of commands

}

or

name() {

list of commands

}


/bin/ksh: Functions (continued)

• can use parameters

• returning from a function

• local variable using typeset

• functions can be recursive


/bin/ksh: ENHANCED JOB CONTROL

• jobs list your jobs

• bg places a specified job in the background

• fg places a specified job in the foreground

• kill sends an arbitrary signal to a process or job

• ^z to stop a foreground job

• stop to suspend a background job


/bin/ksh: coprocess

PIPES

• |& operator supports a simple form of concurrent processing

• cmd |&

cmd run as a background process whose standard input and output channels are connected to the original parent shell via a two way pipe.


The C Shell: /bin/csh• Supports all features described in the Bourne shell

• simple and list variables

• Alias mechanism with arguments

• History mechanism for access of previous commands

• Enhanced job control

• Arithmetic

• directory stack


/bin/csh: STARTUP FILES

• $HOME/.cshrc

• /etc/.login

• $HOME/.login


/bin/csh: simple variables

• set { name [=word]} *

• access–$(name)–${name}–${?name} replaced by 1 if name is set, 0 otherwise


/bin/csh: list variables• Variables to which you can assign a list of values• set { name = ( {word}*) } *

• Access:• $name[selector]• ${name[selector]} selector can be a range

• $#name• ${#name} number of elements in name


/bin/csh: predefined local variables

• $< the next line of standard input fully quoted

• $noclobber prevents existing files from being overridden by >, and non-existent files from being appended to by >>

• $noglob prevents wildcard expansion


/bin/csh: methods for accessing C shell arguments

• $argv a list that contains all of the positional parameters, same as $*

• $argv[1] is equal to $1

• $#argv number of arguments

• $argv[1-n] arguments 1 through n

• $argv[0] illegal, must use $0

• $argv[$#argv] last argument


/bin/csh:file inquiry operator• -option filename

operator meaning r read access

w write access

x execute access

e existence

o ownership

z zero length

f plain file

d directory


/bin/csh: ARITHMETIC EXPRESSION

• Assignment of results of an expression:

• Set variable to expression

@ variable op expression

@ variable[index] op expression

• example:

@ x = 2 + 3

%echo $x

5


/bin/csh:ALIAS• alias [word[string]]• unalias

• to share an alias with other subshells, place it under .cshrc


ARGUMENTS IN ALIASES• C shell assumes that all arguments come at the

end of the alias definition, unless you specify otherwise– Example

• % alias cx chmod +x–% cx * # makes files in all current directory executable

– Two common arguments designations to pass arguments to aliases


/bin/csh alias examplereference: The Unix C shell field

Guide G, Anderson P. Anderson• find requires a single argument, we must

escape ! to suppress interpretation from the C shell

%alias loc 'find ~ -name \!^ -print'

%loc ttydoc77

% alias ldir 'ls -l \!* | grep "^d"'

% ldir ../utils /usr/bin


/bin/csh: history mechanism

• For numbered commands–set prompt = '\! %’

• storage of commands

– set history = 40 size of history file

– set savehist=32 save 32 commands across sessions


/bin/csh: hist mech (continued)• command reexecution

– !! reexecute previous command

– !number

– !prefix

– !?substring

• command editing– %!even :s/pat1/pat2 substitute pat1 with pat2

– %^pat1^pat2 reexecution of previous command substituting pat1 with pat2


ACCESS PORTION OF A FILENAME

• Modifier part of file portion of filename returned

• :h head filename minus trailing path

• :r root filename minus trailing *.suffix

• :e extension trailing .* suffix

• :t tail filename minus leading dir path


/bin/csh: CONTROL STRUCTURES

• foreach ……. end

• if then else endif

• switch case … endsw

• while … end

• onintr [-l label] allows to specify a label to jump to when shell receives a SIGINT


/bin/csh: PIPING

• Process1 |& process2

• Redirects standard output and standard error from process 1 to process 2


/bin/csh:MULTIPLE REDIRECTION

• Cmd >& file send both standard output and standard error to file

• Cmd >&! file same as above, even in noclobber is set

• Cmd >>& file append standard error and standard output to end of file

• Cmd1 | & cmd2 pipe standard error together with standard output

• (cmd > file1) >& file2 send standard output to file1; send standard error to file2


/bin/csh: JOB CONTROL

• Same as ksh, plus• stop suspend background process

• suspend suspend foreground process

• notify notify when current job changes status


/bin/csh: DIRECTORY STACK

• pushd [+number|name]

pushd pushes the directory onto the directory stack

• popd [+number]popd pops a directory from the directory

stack

• dirs: lists the current directory stack .


Effective and efficient shell progreference: Unix shell Tutorial G.Snyder J.R. Mashey

Bell Labs• Minimize number of processes generated

• Find out which cmds are built-in and which are not.

Number of data bytes accessed

Minimize Directory searches

Optimize Directory search order and the PATH variable

Minimize arithmetic and character processing

Avoid command substitution when you can

Move loop invariant outside of loop, especially for command substitution

Documents

UNIX Tools G22.2245-001, Fall 2000