Linux in a Nutshell, Fifth Edition

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Bash and Korn

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Copyright © 2006 O’Reilly & Associates, Inc. All rights reserved.

contain spaces or other special characters. The (( )) form does the

quoting for you. For more information and examples, see “Arith-

metic Expressions,” earlier in this chapter. See also expr in

Chapter 3.

Examples

Each of these examples adds 1 to variable i:

i=`expr $i + 1` All Bourne shells

let i=i+1 Bash, ksh

let "i = i + 1"

(( i = i + 1 ))

(( i += 1 ))

(( i++ )) Bash, ksh93

local

local [options] [name[=value]]

Bash only. Declares local variables for use inside functions. The

options are the same as those accepted by declare; see declare for

the full list. It is an error to use local outside a function body.

login

login [user]

Korn shell only. The shell does an execve(2) of the standard login

program, allowing you to replace one login session with another,

without having to logout first.

logout

logout

Bash only. Exit a login shell. The command fails if the current shell

is not a login shell.

name()

name ( ) { commands; }

Define name as a function. POSIX syntax. The function definition

can be written on one line or across many. Bash and the Korn shell

provide the function keyword, alternate forms that work similarly.

See the “Functions” section, earlier in the chapter.

Example

$ count ( ) {

> ls | wc -l

> }

When issued at the command line, count now displays the number

of files ...